PADI Open Water Diver Manual_01

If this is the first time you’ve used scuba to ven-ture into the underwater world, you’re going tolove it. Immediately, you’ll experience new sensa-tions as you venture into a realm where every-thing looks, sounds and feels a bit different. Thisis part of what makes diving so special; at first

ONE

The Underwater World

The UnderwaterWorld

Dive Equipment

Scuba Systems

The Buddy System

Confined WaterDive Preview

Chapter One 13

Underline/highlight the answers to these questions as you read:

1. What will the buoyancy of an object be (positive, neutral ornegative) if it displaces an amount of water:• more than its own weight?• less than its own weight?• equal to its own weight?

2. Why is buoyancy control, both at the surface and underwater,one of the most important skills a diver can master?

3. What two items control a diver’s buoyancy?

4. How does the buoyancy of an object differ in fresh water com-pared to salt water?

5. How does lung volume affect buoyancy?

MAINObjectives

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you’ll enjoy these sensations because they’re new, buteven after you’ve made hundreds of dives, you’ll findthem an important part of the diving experience.

The new sensations you have underwater result fromphysical differences that arise from being underwa-ter. Becoming a diver depends on understanding howthese principles affect you. In this section, you’llbegin learning about these by looking at buoyancyand pressure. (And, you’ll be learning some extremelyimpressive words you can use to impress your friends.)

BuoyancyHave you ever wondered why a large steel oceanliner floats, but a small steel nail sinks? The answeris surprisingly simple: The ship’s steel hull forms ashape that displaces — pushes aside — much water.The same amount of steel reshaped into a giant nailwould sink, of course, like the regular sized nail. Thisdemonstrates that whether an object floats dependson both its weight and how much water it displaces— its volume.

14 Open Water Diver Manual

Buoyancy.If an object floats, we call it positively buoyant; if itsinks, we call it negatively buoyant; and if it neitherfloats nor sinks, we call it neutrally buoyant.

Built in buoyancy control.When you exhale, you decrease the volume of yourlungs and the amount of water you displace, whichmakes you less buoyant.

Negative

Neutral

Positive

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You can state the principle of buoyancy this way: Anobject placed in water is buoyed up by a force equal tothe weight of the quantity of water it displaces.

This means that if an object displaces an amount ofwater weighing more than its own weight, it willfloat. If an object displaces an amount of waterweighing less than its own weight, it will sink. If anobject displaces an amount of water equal to its ownweight, it will neither float nor sink, but remain sus-pended in the water. If an object floats, we call it pos-itively buoyant; if it sinks, we call it negatively buoy-ant; and if it neither floats nor sinks, we call it neu-trally buoyant. A buoyancy change that makes some-thing more likely to float is called having “more”buoyancy; a change that makes something morelikely to sink is called having “less” buoyancy.

As a diver, it’s important to learn to control yourbuoyancy at the surface and underwater because it

1. An object is positively buoyant when:a. it displaces a volume of waterweighing less than its own weight.b. it displaces a volume of waterweighing more than its own weight.c. it displaces a volume of water weigh-ing equal to its own weight.

2. What two pieces of equipment do you

QUICKQUIZ Self Assessment 1

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You control your buoyancy using two pieces of equip-ment. These are lead weights and a buoyancy controldevice (BCD). You will want to purchase these itemsas soon as possible. You use lead weight in a weightsystem (such as a weight belt or in a weight inte-grated BCD) to adjust your weight. The BCD is adevice that you inflate (increases your volume) ordeflate (reduces your volume) thereby changing yourbuoyancy at any time during a dive. During the con-fined water dives, you’ll learn how to start a divewith the right amount of lead weight, and how toadjust your buoyancy as you need to using your BCD.

lets you control where you are in the water. Forinstance, you’ll learn to establish positive buoyancyat the surface so you can save energy and rest.Underwater, you’ll remain neutrally buoyant most ofthe time — almost weightless, like an astronaut —so you can swim effortlessly and move freely in alldirections. Staying neutrally buoyant keeps you offthe bottom so you avoid injuring delicate aquatic life.

use to control your buoyancy?a. BCDb. finsc. lead weight

3. Buoyancy control is one of the most

Since buoyancy results from the weight of water vol-ume displaced, the heavier the water, the greater thebuoyancy for a given displacement. Salt water (due toits dissolved salts) weighs more than fresh water, soyou’re more buoyant in salt water than in fresh.
important skills you can master
because it allows you to control whereyou are in the water.True False

4. An object will be more buoyant in_______than it would be in ________.a. fresh water, salt water b. salt water, fresh water

5. When you exhale, your lung volume

Without any gear on, most people float in either freshor salt water. When floating motionless at the sur-face, most people need to exhale to sink. When youexhale, you decrease the volume of your lungs andthe amount of water you displace, which makes youless buoyant. You’ll discover during the confinedwater dives that in addition to using lead and yourBCD to control your buoyancy, you can fine-tune yourbuoyancy by breathing more deeply or more shallowly.

Pressure and Your BodyAlthough you don’t usually notice it, air constantlyexerts pressure on you. If you’ve walked against astrong wind, though, you’ve felt its force, demonstrat-ing that air can exert pressure.

Chapter One 15

decreases. This means you have_______ buoyancy.a. moreb. less

How’d you do?1. b 2. a, c 3. True 4. b 5. b.


1. You usually feel pressure only inair spaces because:a. your body is mostly made of pressible liquid, but air is comprand changes volume with presschanges.b. water is denser than air, whicresists pressure better.

2. Pressure changes in water for aascent or descent are much mostantial than the same distanceor descent in air because watermore.True False

How’d you do?1. a. 2. True.

QUICKQUIZ Self Assess

Feel the pressure.You don’t usually feel pressure becauseyour body is primarily liquid, which isincompressible and distributes pressureequally throughout your entire body. Theexception is your body air spaces, whichfeel pressure due to compression of theair inside them.

Underline/highlight the answers to these questions as you read:

6. Why do you usually only feel changing pressure in your bodyair spaces?

7. Why are pressure changes while ascending or descendingunderwater much more substantial than pressure changeswhen ascending or descending the same distance in air?

MAINObjectives

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The air pressure that surrounds you now is simplythe air’s weight — the result of gravity holding theatmosphere against the earth. You don’t usually feelpressure, though, because your body is primarily liq-

uid, which is incompressible and distrib-utes pressure equally throughout yourentire body. The few air spaces your bodydoes have — in your ears, sinuses andlungs — have air inside them equal inpressure to the external air pressure.Although air is compressible, you don’tnotice pressure in body air spaces as longas the pressure’s the same inside and out-side. But if the pressure changes, such aswhen you ascend to and from a higheraltitude by flying or driving throughmountains, the air in body air spaceschanges volume, and you feel it in yourears, and sometimes in your sinuses.

body

incom-essibleure

h

ment 2

givenre sub- ascent weighs

Just as air exerts pressure on you, so doeswater when you submerge. But becausewater is much denser and heavier thanair, pressure changes much more signifi-cantly for a given distance ascent ordescent. As with air pressure, you don’tfeel water pressure except in your bodyair spaces, and one of the first thingsyou’ll notice is that you’ll feel changes

MAINives

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quickly, even when you ascend or descend only a metreor few feet. These changes have some associated prob-lems that you’ll learn to avoid later in this section andduring your confined water dives.

Pressure, Volume and Density RelationshipsAt sea level, the surrounding air pressure remains rel-atively constant. This pressure is a standard referencecalled one atmosphere (ata) because it is theweight/pressure of (but of course) the atmosphere. It’salso called one bar; there’s a slight technical differencebetween an ata and a bar, but it’s so minor that for div-ing applications, we disregard it.

Ten metres/33 feet of water (sea water, to be precise)exerts the same pressure as the atmosphere, or oneata/bar. Therefore, add one ata/bar pressure for every10 metres/33 feet you descend. At 10 m/33 ft, you’reunder two ata/bar — one from air and one from water.At 20 m/66 ft, you’re under three ata/bar, and so on.

If you take an air volume underwater with you in aflexible container or an inverted jar, the volumechanges proportionately with pressure. If you descendto 10 m/33 ft, you double the pressure (two ata/bar)and halve the volume. At 20 m/66 ft — three ata/bar —you have one third the volume, and so on.

Chapter One 17

Depth

0m/0ft

10m/33ft

20m/66ft

30m/99ft

Pressure

1 bar/ata

2 bar/ata

3 bar/ata

4 bar/ata

Air and water.Ten metres/33 feet of sea water exerts thesame pressure as one atmosphere, or onebar/ata. Therefore, you add one bar/atapressure for every 10 metres/33 feet you descend.

Underline/highlight the answersto these questions as you read:

8. What is the relationshipbetween increasing anddecreasing depth and waterpressure?

9. What are the absolute pres-sures, in atmospheres or bar,for:• 10 metres/33 feet?• 20 metres/66 feet?• 30 metres/99 feet?• 40 metres/132 feet?

10. What is the relationshipbetween air volume and den-sity, and how do they varyaccording to this relationshipwhen pressure increases ordecreases?

Object

Depth

0m/0ft

10m/33ft

20m/66ft

30m/99ft

Pressure

1 bar/ata

2 bar/ata

3 bar/ata

4 bar/ata

Air Volume

1

1/2

1/3

1/4

Air Density

x 1

x 2

x 3

x 4

Same air, smaller space.If you take an air volume underwater with you in a flexible containeror an inverted jar, the volume changes proportionately with pressure.

Density also changes proportionately when pressurechanges. When you double the pressure and halve the airvolume, the volume reduction comes from squeezing thesame number of air molecules into half the space. So,the density doubles. When you triple the pressure (20 m/66 ft), you triple the density. Hope you’re picking up a pattern here.

To maintain theair volume as youdescend, you needto add air to thespace to keep upwith the volumereduction. This isthe concept behindequalization (moreabout this in amoment); the airyou need to add isproportional to thepressure increase.

As you’ve probably already figured out, air expands pro-portionately as you ascend and the pressure decreases. Ifyou take an air volume to 30 m/99 ft — four ata/bar — itcompresses to one fourth its surface volume. When youreturn to the surface, the air expands to its original volume.

Air Depth Pressure Volume 0m/0ft 1 bar/ata Full

10m/33ft 2 bar/ata 1/2 Full




Think thicker.Air density also changes proportionatelywhen pressure changes.Twice the pressure, half

the volume.An inverted open bottle of air taken from the surface to 10 metres/33 feet shows the effects of pressure. The pressurecompresses the air volume to half what it was at the surface. Because the samenumber of air molecules take up half thespace, the air density doubles.

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Depth

0m/0ft

10m/33ft

20m/66ft

30m/99ft

Pressure

1 bar/ata

2 bar/ata

3 bar/ata

4 bar/ata

Air Volume

1

1/2

1/3

1/4

Surface Volume

Equivalent

x 1

x 2

x 3

x 4

More air.To maintain the air volume as you descend, you need to add air tothe space to keep up with the volume reduction.

If you added air to the space to maintain its volume, theair you added expands when you reduce the pressure aswell. If the air is in an open container, the expanding airsimply bubbles out into the surrounding water. In a closed,flexible container like a plastic bag or a balloon inflated atdepth, the air volume grows proportionately with thedecreasing pressure. If you inflated the bag at 30 m/99 ft,it will be four times as big atthe surface — provided it canstretch that much! Otherwise,the bag will burst duringascent; this has importantimplications regarding yourbody air spaces that we’ll lookat shortly.

Depth

0m/0ft

10m/33ft

Pressure

1 bar/ata

2 bar/ata

Air Volume of closed container

x4

x2

x1 1/3

x1

S

Closed Container no air can escape

Open Container air can escape

n volume expands when you reduce thee excess expanding air simply bubbles out intoexible container the air volume grows propor-re. If you inflated a sealed bag at 30 m/99 ft, it on the way to the surface, or burst during.

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The Effects of Increasing PressureBased on what you’ve justlearned, we can look at howthe relationships betweenpressure, volume and densityaffect your body air spaceswhile diving. The air spacesthat concern you as a diverare the natural ones in yourbody, and those artificially created by wearing dive equip-ment. The two major air spaces within your body mostnoticeably affected by increasing pressure are your earsand sinuses. The major artificial air space most affected byincreasing pressure is the one created by your mask.

20m/66ft

30m/99ft

3 bar/ata

4 bar/ata

Bursting a bag.Air added to an air space to maintaipressure. With an open container, ththe surrounding water. In a closed, fltionately with the decreasing pressuwill expand to four times the volumeascent if it cannot stretch that much

During descent, water pressure increases and com-presses the air in your body air spaces. As the vol-ume decreases, the pressure pushes body tissues

in, toward the air space, which you feel in your ears,sinuses and mask. If you continue to descend, thisbecomes uncomfortable, and with continuing descent, pos-sibly even painful. This is called a squeeze on the air space.
You may have felt a squeeze in your ears when diving tothe bottom of a swimming pool. A squeeze, then, is a pres-sure imbalance in which pressure outside an air space
Chapter One 19

20 Op

Mask Air Space

Sinus Air Space

Ear Air Space

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exceeds pressure inside an air space, result-ing in pain or discomfort. Besides the ears,sinuses and mask, it’s possible to experience a squeeze in the lungs, teeth or any other air space. Fortunately, you can easily avoid squeezes.

To avoid discomfort, you keep the volume inan air space normal by adding air to it duringdescent, keeping the air space pressure equalto the water pressure outside. This is calledequalization. Your ear and the sinus airspaces connect to the throat, allowing you touse air from your lungs to equalize them. Youequalize the air space in your mask throughyour nose.

Although very rare, it’s possible for an air space to develop in filled teeth wherethe tooth or filling has continued to erode.During descent, the increasingpressure pushing in on this smallair space causes a tooth squeeze.In most cases, the discomfort willcause you to stop descending. Youcan’t equalize an air space undera tooth filling, but your dentistcan eliminate the space, and reg-ular dental checkups help avoidthe problem altogether.

Although an air space, yourlungs are large and flexible andnot very prone to a squeeze. As ascuba diver, you automaticallyequalize your lungs as youbreathe continuously from yourscuba equipment. When you skindive, holding your breath, thepressure compressing your lungshas no effect, provided youstarted with a good breath. Theydrop in volume during descent

en Water Diver Manual

Depth Pressure Volume Density

0m/0ft x 1 x 1

10m/33ft 2 bar/ata

30m/99ft 1/4

40m/132ft 5 bar/ata x 5


Complete the following chart for a sealed flexible bag fullof air at the surface.

How did you do? (Answers appear in bold type)0m/0ft Depth: 1 bar/ata, x 1, x 1.10m/33ft Depth: 2 bar/ata, 1/2, x 2.30m/99ft Depth: 4 bar/ata, 1/4, x 4.40m/132ft Depth: 5 bar/ata, 1/5, x 5.

Mainly in your head.The two major air spaces within your bodymost noticeably affected by increasingpressure are your ears and sinuses. The majorartificial air space most affected by increasingpressure is the one created by your mask.

and re-expand during ascent tonearly their original volume whenyou reach the surface, having usedan inconsequential amount toequalize other air spaces.

If you were to breath hold divestarting with empty lungs (youexhale, then dive) severalmetres/feet, or descend really deep (like 60 metres/200 feet) hold-ing your breath, there’s a theoretical possibility that you could squeeze your lungs – but these arerather unlikely situations for most divers.

Another air space you might need to equalize is adry suit, which holds a layer of air around yourbody for maximum warmth. If you’re going to use adry suit as part of this course, your instructor willshow you how to equalize it. If you’re not familiarwith them, Section Two describes dry suits in more detail.

Air from

Lungs

ht the answers to these questions as you read:

three major air spaces affected by pressure?

ueeze”?

lization”?

e ways you can equalize air spaces during

ould you equalize during descent?

eps should you take if you feel discomfort in anle descending?

MAINbjectives

Equalize to stop the squeeze.Pressure pushes body tissues in toward theair space, which you feel in your ears, sinusesand mask. If you continue to descend, thiscauses a squeeze on the air space. To avoiddiscomfort, you keep the volume in an airspace normal by adding air to it duringdescent. This is called equalization. Your earand the sinus air spaces connect to thethroat, allowing you to use air from your lungs to equalize them.

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Equalization techniques.The air spaces in your earsare the most sensitive toincreasing pressure, butassuming you’re in goodhealth (no head cold orallergy congestion) you caneasily equalize them. To dothis, pinch your nose shutand gently blow against itwith your mouth closed; thisdirects air from your throatinto your ears and sinus airspaces. Another technique isswallowing and wiggling thejaw from side to side. A thirdtechnique combines these —swallow and wiggle your jawwhile blowing gently againstyour pinched nose.

Underline/highlig

11. What are the

12. What is a “sq

13. What is “equa

14. What are thredescent?

15. How often sh

16. What three stair space whi

O

Chapter One 21


Prevention is the ticket.Equalize every metre/few feet whiledescending, before you feel discomfort. If youfeel discomfort in an air space, ascend untilthe discomfort eases, equalize and continue aslow descent equalizing more frequently.

Unequalizable.Ear plugs or a too-tight wet suithood can create an air spacebetween your ear drum and theplug/hood that you can’t equalize.

If you have ear discomfort orother equalization problems, besure to signal your buddy orinstructor immediately. Yourbuddy or instructor have no wayof knowing that you have aproblem unless you signal.

Signal if youCan’t Equalize!Signal if youCan’t Equalize!

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Equalize every metre/few feet while descending,before you feel discomfort. If you wait until youfeel discomfort, you may not be able to equalizebecause water pressure may be great enough to hold
the air passages shut. Instead, if you feel discomfort inan air space, ascend until the discomfort eases, equalizeand continue a slow descent equalizing more fre-quently. You’ll find it easier to equalize with experience.
If you can’t equalize, discontinue the dive. Continuingto descend with an unequalized air space may result ina ruptured ear drum or similar injuries. Neverattempt a forceful or extended equalization —that can also cause serious ear injuries, including aruptured ear drum, which can cause vertigo. Shouldthis occur, abort the dive. If ascending a metre/few feetand trying again doesn’t permit you to equalize, don’tforce it. Be patient and gentle, or end the dive and tryanother day.

Congestion (due to colds or allergies) can plug air pas-sages, making equalization difficult or impossible.Medications, such as sprays and decongestants, mayclear the openings, but you shouldn’t do this and divebecause the medication may have undesirable sideeffects (such as drowsiness) and may wear off whileyou’re diving, creating equalization problems when youtry to ascend.

You can also create an unequalizable space in your earcanal, either by wearing a too-tight wet suit hood thatinadvertently seals against your ears, or by wearingear plugs. In either case, you end up with an air spacebetween your ear drum and the plug/hood that youcan’t equalize. To prevent this, pull your hood awayfrom your ears momentarily to allow the pressure toequalize, and never wear ear plugs while diving. Theonly exceptions are special ear protectors made specifically for scuba diving that allow for pressureequalization.

You equalize the air space in your mask by simplyexhaling into it through your nose. If you forget to

equalize your mask, you’ll feel a mask squeeze,which is a pulling sensation on your face andeyes. You’ll probably find that mask equalizationbecomes something you do automatically. Notethat since your nose has to be inside the mask toequalize it, you can’t use swimmer goggles forscuba diving – they don’t enclose your nose andcannot be equalized. When you buy a mask, keepthese considerations in mind.

The Effects of Decreasing PressureAs you read in the discussion on squeezes, yourlungs experience no harmful effects from changesin pressure when you’re holding your breathwhile skin diving. You take a breath and descendand the increasing water pressure compressesthe air in your lungs. During ascent, this air re-expands so when you reach the surface, your lungsreturn to approximately their original volume.

1. The three major air spaces affected by pres-sure when you descend are:a. sinuses, lungs, stomachb. mask, ears and sinusesc. lungs, mask and ears

2. A squeeze is:a. a pressure imbalance in which pressureinside an air space exceeds pressure outsidean air space, resulting in pain or discomfort.b. a pressure imbalance in which pressureoutside an air space exceeds pressure insidean air space, resulting in pain or discomfort.

3. Equalization is adding air to an air space asyou descend so the pressure in an air spaceequals the surrounding water pressure.True False

4. Which are techniques for equalizing yourears? (Check all that apply.)a. Pinch your nose and blow gently against it.b. Swallow and wiggle your jaw from side tosidec. Make a loud noise.d. None of the above.

5. You want to equalize your ears:a. when you feel discomfort.b. every metre/few feet before you feel dis-comfort.c. only if they hurt enough to bother you.

6. If you feel discomfort and can’t equalize,ascend until you relieve the discomfort andtry again. Don’t be forceful in equalizing. Ifyou can’t equalize, discontinue the dive.True False

How’d you do?1 b. 2. b. 3. True. 4. a, b. 5. b. 6. True.


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Expanding air can cause lung over ex-pansion (lung rupture), the most seriousinjury that can occur to a diver. For this reason,the most important rule in scuba diving isto breathe continuously and never, neverhold your breath. Lung over pressurization

When you scuba dive, however, the situation dif-fers dramatically. Scuba equipment allows you tobreathe underwater by delivering air at a pres-sure equal to the surrounding water pressure.This means your lungs will be at their normalvolume while at depth. This air will expand whenyou ascend.

If you breathe normally, keeping the airway toyour lungs open, no problem. Expanding airescapes during ascent and your lungs maintaintheir normal volume. But, if you were to holdyour breath, blocking your airway while ascend-ing, your lungs would overexpand, much like thesealed bag or balloon filled at depth and taken tothe surface.

Chapter One 23

Most importantrule of scubadiving!The lungs can beinjured by even slightpressure changes if youhold your breath —even as little as ametre/two orthree feet. So,it’s important toalways breathecontinuouslywhen usingscuba, even inshallow water.


Underline/highlight the answers to these questions asyou read:

17. What is the most important rule in scuba diving?

18. What are the consequences of breaking the mostimportant rule in scuba diving?

19. What is a “reverse block”?

20. What should you do if you feel discomfort duringascent due to air expansion in the ears, sinuses,stomach, intestines or teeth?

MAINObjectives

Depth

0m/0ft

10m/33ft

20m/66ft

30m/99ft

Pressure

1 bar/ata

2 bar/ata

3 bar/ata

4 bar/ata

Closed Container no air can escape

Open Container air can escape

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will occur unless you permit the pressure toequalize by breathing normally at all times.Lung over expansion can force air into thebloodstream and chest cavity, which can lead to severe injuries including paralysisand death.

Some people find they have a naturaltendency to hold their breath whenthey first begin learning to use scuba, butthis tendency must be changed. The lungscan be injured by even slight pressurechanges if you hold your breath — even aslittle as a metre/two or three feet. So, it’simportant to always breathe continuouslywhen using scuba, even in shallow water.

Although lung overexpansion injuries arevery serious and among the most difficultdiving injuries to treat, they are also amongthe easiest to avoid: Simply breathe at alltimes and do not hold your breath whenusing scuba. During your confined waterdives you’ll practice some skills during whichyou take the scuba regulator out of yourmouth, but even then you don’t hold yourbreath. Instead, you’ll learn to exhale a slow,steady stream of bubbles any time the regu-lator isn’t in your mouth.

Your other air spaces generally pose no prob-lems during ascent. Normally, expanding airreleases from these without any consciouseffort. It is possible, though, to feel pain anddiscomfort in your ear and sinuses whileascending due to a reverse block, sometimescalled a “reverse squeeze.” A reverse blockoccurs when expanding air cannot escapefrom an air space during ascent. In this case,you feel discomfort because the pressureinside the air space exceeds the surroundingwater pressure.

Read my lips.During your confined water dives you’ll practiceskills during which you take the regulator out ofyour mouth. So you don’t hold your breath, youexhale a slow, steady stream of bubbles.

Won’t come out.A reverse block occurs whenexpanding air cannot escapefrom an air space during ascent.In this case, you feel discomfortbecause the pressure inside the air space exceeds thesurrounding water pressure.

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Reverse blocks are uncommon and generallyresult from diving with congestion cleared bymedication, and having the medication wear offwhile underwater. To avoid this, don’t dive witha cold or allergy congestion, even if you usedecongestants or other medication.

Gas forming in the stomach or intestines dur-ing diving can also expand during ascent andcause discomfort if it doesn’t pass. This isn’tvery common, and you can usually prevent itby avoiding gas-producing foods prior to diving.Some people tend to swallow air when breath-ing through their mouths at depth; this canalso expand during ascent and cause some dis-comfort. If you find this applies to you, payingattention to your breathing and swallowing willusually break the habit.

It is possible, though very rare like a toothsqueeze, for a reverse block to occur in an airspace under an inadequate tooth filling or atooth filling with secondary erosion. Air slowlyseeps into the space during the dive, and can’tescape quickly enough when you begin toascend. You avoid this reverse block, like toothsqueeze, through regular dental checkups.

If you feel any reverse block discomfort —whether in your ears, sinuses, stomach, intes-tines or teeth — slow or stop your ascent,descend a metre/few feet and give the trappedair time to work its way out. If you experiencesevere or frequent reverse blocks, see a physi-cian knowledgeable about dive medicine.

The Effects of Increased Air DensityTell your friends that you’re learning to scubadive, and at least one will ask you how long youcan stay underwater with a scuba tank. Apolite answer is, “Oh, around an hour, give ortake,” but as you’ll see, the technically correct

Chapter One 25

answer is, “It depends.” That is, it dependson how deep you dive (as well as yourbreathing rate).


1. The most important rule in scuba diving is:Breathe continuously and never hold your breath.True False

2. Ascending while holding your breath (check allthat apply):a. can cause lung over expansion injuries.b. can cause serious injuries, including paraly-sis and death.c. causes injuries that are easy to avoid by notholding your breath.

3. A reverse block is:a. pain and discomfort caused by expanding airtrapped inside an air space during ascent.b. pain and discomfort caused by outside pres-sure on an air space.

4. If you feel discomfort during ascent due to areverse block, you should:a. slow or stop your ascent and give thetrapped air time to work its way out.b. descend to compress the air and allow it toshift to some other area of the body.c. None of the above.

How’d you do?1. True. 2. a, b, c. 3. a. 4. a.


Underline/highlight the answers to these ques-tions as you read:

21. How does increasing depth affect how longyour air supply lasts?

22. What’s the most efficient way to breathedense air underwater?

MAINObjectives

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Scuba gear supplies air equal to the sur-rounding pressure. So apply what youlearned earlier about pressure and an airvolume, and you’ll see that you consumeyour air faster as you go deeper. For exam-ple, the pressure at 20 metres/66 feetequals three bar/ata, so for each breathyou need three times the number of airmolecules to fill your lungs to the samevolume. Therefore, all other factors equal,your air supply lasts only one third as longat 20 m/66 ft as it does at the surface.

Likewise as you’ve learned, the deeper youdescend, the denser the air becomes.Dense air is harder to inhale and exhale

than air at normal surface pressure and density,with the effort increasing exponentially the fasteryou try to breathe it. That is, it takes about fourtimes the effort to breathe twice as fast. So, youwant to take deep, slow breaths while breathingdense air while diving. For maximum air conserva-tion, save energy and don’t over exert yourself.Pace yourself so that you breathe normallythrough your entire dive. Relax. You should

In this subsection on the Underwater World,you learned:

▲ Whether an object sinks, floats or doesneither in water depends on its weightand its displacement.

▲ You’ll use lead weight and a BCD, aswell as lung volume, to control yourbuoyancy.

▲ The body is made up mostly of incom-pressible liquid, so you only feel pres-sure on the air spaces, which hold com-pressible air.

▲ There’s a proportional relationship be-tween pressure, air volume and density.

▲ You can use one of three techniquesevery metre/few feet to equalize yourears to prevent a squeeze while

Summary PointsSummary Points

OWDM_013_043.qxd 2/23/06 11:54 AM Page 27

never be out of breath while diving — divingis exciting and adventurous, but its not sup-posed to get you winded underwater.

Dept

h

Pres

sure

AirV

olum

e

Surfa

ceVo

lum

eEq

uiva

lent

0m/0ft

10m/33ft

20m/66ft

30m/99ft

1 bar/ata

2 bar/ata

3 bar/ata

4 bar/ata

1

1/2

1/3

1/4

x 1

x 2

x 3

x 4

Deeper = faster.Scuba gear supplies air equal to the surrounding pressure.This means you use your air faster as you go deeper.

By this point you realize you need equipmentto dive. You may be well on your way to own-ing a complete set. So, you’re probablyalready familiar with basic types of diveequipment. But you may not be as familiarwith some of the specific features or optionsthat apply to each type, or what separatesequipment aimed primarily at snorkelingfrom equipment intended for scuba diving.Also, you may not yet be aware of someequipment you’ll use. This subsection looksat equipment basics for masks, snorkels, fins,BCDs, scuba tanks, regulators and sub-mersible pressure gauges, each of whichyou’ll use during your confined water dives.

Chapter One 27

descending.

▲ You exhale into your mask through yournose to prevent a squeeze.

▲ Never continue to descend if you can’tequalize.

▲ The most important rule in scuba divingis to never hold your breath.

▲ Don’t dive with a cold or allergy conges-tion, even with decongestant.

▲ The deeper you go, the faster you useup your air supply.

▲ When scuba diving, breathe slowly anddeeply, and avoid getting out of breath.

Dive Equipment

While you’ll learn the basics here, keep in mindthat dive gear comes in myriad styles and col-ors that makes it comfortable and stylish aswell as functional. What types work best foryou will depend on your preferences, the typeof dive activities that interest you, where you’llbe diving and other variables. Your PADI DiveCenter, Resort or Instructor can show you thedifferent types and models that best suit your needs.

28 Open Water Diver

1. As you gofrom youra. slower.b. faster.c. the sam

2. The most ing underwTrue

How’d you do1. b, 2. False

QUQUIZ


23. Why does a diver need amask?

24. Why does the mask need toenclose your nose?

25. What six features should youlook for in a mask?

26. When buying a mask, whatare the two most importantfactors?

27. How do you prepare a newmask for use?

28. What three general mainte-nance procedures apply tomask care?

MAINObjectives

OWDM_013_043.qxd 2/23/06 11:54 AM Page 28

MasksPurpose. It’s not earth-shattering news thatyou need a mask to see underwater. Why youneed it is that light behaves differently inwater than in air, and your eyes focus accord-

ing to how lightbehaves in air.That’s why watermakes everythingblurry. The maskcreates an air spaceso your eyes canfocus.

ICKSelf Assessment 6

deeper, you consume air

Formorein

formationabout...

Dive EquipmentSee the PADI Encyclopedia ofRecreational Diving and the PADIMultimedia Encyclopedia CD-ROM

As you learned, themask creates an airspace you mustequalize duringdescent to preventmask squeeze.That’s why themask must encloseyour nose. Goggles,which cover onlythe eyes without

enclosing your nose can’t be equalized. They’refine for surface swimming, but they’re notacceptable for diving.

scuba tank:

e.

efficient method for breath-ater is rapid and shallow.False

?.

When buying a mask, don’t skimp. Get a goodone specifically designed for scuba diving thatfits you properly. If you think about it, in warm

Manual

water you can have a lot of fun with only a mask,but if you had every piece of dive gear but a mask,

there’d be no reason to get in the water. Soyour mask is important.

Styles. Mask styles range from simple roundor oval-shaped models to more modern styleswith lower internal volumes and wider fieldsof vision. Wraparound masks feature twopanels along the sides to improve peripheralvision. The vast majority of masks you’llchoose from are lower-profile masks, whichhave a notched face plate and a nose pocketto allow your nose to protrude past the lens.This gets the lens closer to your face, for awider vision field, plus makes it easy topinch your nose for equalizing. Many wrap-around type masks incorporate low-profile design.

Owning your equipment. The complete diver.Dive gear comes in myriadstyles and colors that makes itcomfortable and stylish as wellas functional. What types workbest for you will depend onyour preferences, the type ofdive activities that interest you,where you’ll be diving andother variables.

Snorkel

Cylinder

Scuba fins

Buoyancy controldevice with low-pressure inflator

Plastic divetables and slate(in pocket)

Full-length wetsuit with farmerjohn bottoms

Window on the underwaterworld.The vast majorityof masks you’llchoose from arelower-profilemasks, whichhave a notchedface plate and anose pocket toallow your noseto protrude past the lens.

OWDM_013_043.qxd 2/23/06 11:54 AM Page 29

Features. Masks intended for scuba diving have these features:

1. Tempered-glass lensplate. If broken, tem-pered glass is lesslikely to shatterinto fine, hazardous slivers.

2. Comfortableskirt with a closefit against your faceand a good seal.

3. Nose or fingerpockets. To makeequalizing your earseasier, a mask shouldhave some way of lettingyou conveniently pinch or block your nose.

Mask

Primary regulatorsecond stage

Alternate air sourcesecond stage

Instrument consolewith pressure gauge,depth gauge, divetimer and compass(on back)

Weight belt withweight retainersand quick-releasebuckle

Chapter One 29

30 Open Wate

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4. Low-profile. The lower the profile of the mask, the lessair you need to equalize it and to clear if it floods, but themain benefit is that it gives you a wider vision field.

5. Adjustable strap that can be locked in place.

6. Wide field of vision. This is accomplished through lowprofile and/or wraparound design.

An optional featureyou might find in afew masks is a purgevalve. A purge valve isa one-way valve usedfor clearing waterfrom a mask. It’s easyto clear water from amask without a purgevalve, so consider itoptional, but it’s a nice extra feature if the mask suitsyou in every other way.

Materials. Masks for scuba diving are most often madefrom silicone rubber. Silicone rubber is usually translu-cent, though manufacturers sometimes add coloringagents to make it black, or a translucent color, which isprimarily to make the mask look better. Why not be styl-ish and functional?

At one time you could find masks made from black or col-ored neoprene rubber, but these have all but vanished,even in inexpensive models. This is because silicone laststhree to four times longer than neoprene, is generallysofter and more comfortable, usually looks better, anddoesn’t usually irritate sensitive skin. You may see neo-prene masks in use, but they tend to be the exceptionrather than the rule.

r

Six features found in masksfor scuba diving.

ComfortableSkirt

AdjustableStrap Low

Profile

TemperedGlass

WraparoundDesign

Nose Pocketor Finger Pocket

Selection and Purchase. When buying any equipmentfor scuba, your two most important selection factors arefit and comfort. This is particularly true for your mask,because a mask that doesn’t fit well will leak and/or irri-tate you and take the fun out of the dive. (Note: You

Diver Manual

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needn’t suffer for style. Dive equipment comes in enoughvariety that you can accommodate fit and comfort first,yet still look good. (You can buy almost everything inbasic black, too.)

To test a mask for a proper fit, use the “sniff”test. Place it gently against your face withoutusing the strap and inhale through your nose.A properly fitting mask will pull into place bysuction and stay as you inhale. If you have topush or twist the mask to make it seal, try adifferent one. After finding some that fit, trypinching your nose with each on to see whichis easiest.

If you need visual correction, some masksaccept prescription lenses. You’ll want to thinkabout this when buying a mask, because notall masks do this readily. Your PADI Dive Center, Resortand Instructor can help you pick out a mask that’s rightfor you.

Stuck on you.To test a mask for a proper fit, use the “sniff”test. Place it gently against your face withoutusing the strap and inhale through your nose.A properly fitting mask will pull into place bysuction and stay as you inhale.

See clearly.

Preparation for Use. Manufacturers coat newmasks with a protective chemical that youneed to scrub off or you won’t be able to defogthe mask. To remove the film, use a soft clothto gently scour the glass inside and out with anon-gel toothpaste or other low abrasioncleaner with fine grit that can remove the filmwithout scratching the glass. Be sure to do thisbefore your confined water dive.

Next, adjust the mask strap for a comfortablefit across the crown of your head. The strapshould be snug, but not tight, and make sureto close the locking device (they differ a bitfrom one mask to another) so it doesn’t slip.

To remove the chemical film from manufacturing,th to gently scour the glass insidea non-gel toothpaste or other lowner with fine grit that can removeut scratching the glass.

Maintenance. Three general maintenance pro-cedures apply to caring for all dive equipment,including masks: 1) rinse thoroughly withfresh water after each use (even in a swimming pool), 2)keep out of direct sunlight and 3) store in a cool, dry place.

use a soft cloand out with abrasion cleathe film witho

Chapter One 31

The freshwater rinse removes salt, chlorine and/orminerals that contribute to corrosion and deteriora-tion. Rinse thoroughly as soon as possible after div-ing; if you can’t rinse your gear right away, it’s gen-erally better to keep it wet than to let salt water dryon it because it’s much harder to remove salt after it dries.

Sunlight damages silicone (and especially neo-prene), so avoid leaving your equipment in directsunlight. If it has to stay out in direct sunlight at adive site or on a boat, you can throw a beach towelover it. Dry your equipment thoroughly before stor-ing it in a cool, dry place away from hydrocarbonsand ozone.

Keep masks and other dive equipment made fromsilicone out of contact with neoprene. The neopreneleaches into the silicone and discolors it, which doesn’t harm it functionally, but makes it look less attractive.


1. You need a mask to see underwaterbecause:a. the human eye can’t focus in water.b. the mask specially filters the lightunderwater.c. the mask is an important part oflooking really sharp.

2. A mask needs to enclose your nose:a. for a better field of viewb. so you can equalize the mask.c. so you can pinch your nose andequalize your ears.

3. The six features you look for in amask include (check all that apply):a. low profileb. purge valvec. nose or finger pocketsd. wide vision field

4. The most important factors whenbuying a mask (and other dive gear)are:a. style and color.b. fit and comfort.

5. To prepare a new mask for use(check all that apply):a. scrub off the protective film leftfrom manufacturingb. adjust the strap

6. Maintenance for your mask (andmost dive gear) includes (check allthat apply):a. rinsing in fresh water after use.b. storing in a cool, dry place.c. drying thoroughly in the sun.

How’d you do?1. a. 2. b. 3. a, c, d. 4. b. 5 a, b. 6 a, b.


OWDM_013_043.qxd 2/23/06 11:54 AM Page 32

SnorkelsPurpose. Since scuba divers have a tank and regu-lator, you may wonder why a snorkel is a standardpiece of scuba gear. Actually, you want a snorkel fora few reasons when you scuba dive. First, it lets yourest or swim with your face in the water, like whenyou’re looking for something below, without wastingtank air. Second, when there’s a bit of surface chop,splashing waves can get in your mouth if you don’thave a snorkel, but the snorkel is usually highenough to get above these. Third, if you run low onair away from the boat or shore, it makes it easier toswim back, again resting with your face in the water.

When you’re skin diving or snorkeling, the snorkelpermits you to view the underwater world continu-ously, without the interruption of having to lift yourhead for a breath. You can stay in the water all dayresting with your face in the water, but you tirequickly if you keep having to raise your head tobreathe. Try it and see.

Styles. Snorkels suitable for scuba diving aresimple devices – at the most basic level, they’relittle more than a mouthpiece and tube that fitscomfortably in your mouth and extends above the surface. They are available with a variety of features.

Underline/highlight the answers to these ques-tions as you read:

29. Why does a diver need a snorkel?

30. What three features does an easy-breathingsnorkel have?

31. When purchasing a snorkel, how do youcheck it for fit and comfort?

32. How do you prepare a new snorkel for use?

MAINObjectives

Breathe easy.Your snorkel is standard equipment for scubadiving because it allows you to rest at the surfacewith your face in the water, and allows you to savetank air when swimming on the surface.

OWDM_013_043.qxd 2/23/06 11:54 AM Page 33

Features. Look for an easy breathing snorkel.The snorkel’s tube diameter (bore), length andshape affect breathing resistance, so generallylook for:

1. A large bore — so it’s not like trying to breathethrough a soda straw.

2. Not excessively long — If a snorkel’s too long, it’s hard to clear and you rebreathe a lot ofyour air. About 43 cm/17 in, give or take, is asuitable length.

3. Designed with smooth, rounded bends — sharpbends add breathing resistance.

Today’s popular snorkels have other features:they fit closely to the contours of your head tominimize drag, and most have an optional self-draining feature. This feature makes it easier toclear water from your snorkel at the surface.Some snorkels have a flexible lower portion thatallows the mouthpiece to comfortably drop awayfrom the mouth area when you’re not using it. Afew snorkels have splash guards on the top tohelp keep the snorkel dry. All of these featuresare fine if you want them, as long as they don’tinterfere with easy breathing.

Materials. Most snorkels sold today are madefrom a combination of silicone and plastic. Theupper portion of the snorkel (the barrel) is usu-ally constructed of semirigid plastic tubing. Thelower portion and mouthpiece are usually madefrom silicone rubber. You can find snorkels in avariety of colors to match your mask.

Chapter One 33

Selection and Purchase. Choose your snorkel basedon comfort, fit and minimal breathing resistance. Tocheck for these, place the snorkel in your mouthwith the mouthpiece flange between your lips andteeth, and the barrel of the snorkel against your leftear. You should be able to adjust the mouthpiece tofit comfortably, without chaffing or causing jawfatigue, while sitting straight in your mouth. Yourinstructor, dive center or resort can help you buy anappropriate snorkel.


Features in snorkels used for scubadiving.

High tech tubes.Most snorkels sold today are made from acombination of silicone and plastic. Thebarrel is usually constructed of semirigidplastic tubing. The lower portion andmouthpiece are usually made fromsilicone rubber.

LargeBore

Designed withSmooth Bends

FlexibleTube

SelfDrainingBarrel

NoLonger

than 17 in.

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Preparation for Use. Attach the snorkel to the leftside of your mask (because your regulator comesfrom the right). You do this with a clip or slot on thesnorkel, or with a snorkel keeper that comes with it.Adjust the snorkel and snorkel keeper so the top ofthe snorkel sits at the crown of your head with themouthpiece in place. You should be able to relaxyour jaw without losing the mouthpiece.

Maintenance. As with the mask, rinse your snorkelafter each use and store it in a cool, dry place andkept out of direct sunlight. Store it away from neo-prene rubber to prevent staining of silicone parts.

Everything in its place.

FinsPurpose. Fins provide alarge surface area so yourpowerful leg muscles canmove you through thewater. This is muchmore effective thanswimming with yourarms, though there aredivers with limited leg usewho use their arms with spe-cial hand fins.

All fins, regardless of styleor features have pockets foryour feet and blades forpropulsion.

Adjust the snorkel and snorkelkeeper so the top of the snorkel sitsat the crown of your head with themouth-piece in place. You should beable to relax your jaw without losingthe mouthpiece.

Styles. Modern fins come in two basic styles:adjustable strap and full-foot. Adjustable fins haveopen heel foot pockets and adjustable heel straps,whereas full-foot fins enclose the heel and fit likerubber slippers.

Mausewitstrrubial

1. You need a snorkel when scubadiving (check all that apply):a. to conserve air while swimmingor resting at the surface.b. to make it easier to breathewhen the surface is a bit rough.c. in case you have a long swimwith an empty tank.

2. An easy breathing snorkel haswhich features? (Check all thatapply):a. large boreb. really long tubec. smooth, rounded bends

3. A properly adjusted snorkel (checkall that apply):a. has the opening near your fore-head.b. remains in your mouth with arelaxed jaw.c. sits on the left side of yourmask.

How’d you do?1. a, b, c. 2. a, c. 3. b, c.


OWDM_013_043.qxd 2/23/06 11:54 AM Page 35

Most scuba divers wear adjustable fins becauseyou can wear wet suit boots with them. Also, mosthigh-power fins appropriate for scuba diving areadjustable strap types, though there are excep-tions. Warm water snorkelers and scuba diversoften prefer full-foot fins because they don’t needwet suit boots.

Features. Fins have several features to choosefrom, especially blade design features. Blade fea-tures include ribs, which add rigidity to the bladeand act as vertical stabilizers; vents, which reduceresistance to fin movement and increase efficiency;and channels, which increase efficiency by guid-ing water smoothly overthe fin. Split fins aredesigned to thrust waterstraight back for maxi-mum efficiency. (You canhave long, passionatedebates with fellowdivers over which ofthese offers the best per-formance, but while thisgives you something todo when you can’t go div-ing, the reality is that all

the top fins offer comparableperformance when you wearthe best fin for you.)

Underline/highlight the answers tothese questions as you read:

33. Why does a diver need fins?

34. What are the two basic finstyles?

35. What blade design featuresmay enhance a fin’s perfor-mance?

MAINObjectives

terials. Most modern fins a composite construction,h foot pockets and heelaps made from neopreneber (or a similar mater-

), and the blade made from

Chapter One 35

36. How do you prepare new finsfor use?

37. What three considerations doyou have when buying a spe-cific type of fin?

an appropriate plastic. However, non composite, all-neoprene fins remain popular even as neoprene fadesfrom use in other dive equipment. Neoprene fins lasta long time and have performance characteristicsmany divers prefer. Divers who prefer composite finslike the fact they’re lighter in weight, may havegreater propulsion efficiency and you can buy themin a variety of colors to match your mask andsnorkel. Composite fins may affect your buoyancycompared to all neoprene fins because they’re lighter.

In looking at fins that accommodate your size, physi-cal ability and where you intend to use them, yourprimary concerns are (you guessed it) fit and com-fort. If you’re not sure what model to select, have yourPADI Instructor, Dive Center or Resort help you.


Foot power.Modern fins come in two basic styles:adjustable strap and full-foot. Adjustablefins have open heel foot pockets andadjustable heel straps, whereas full-footfins enclose the heel and fit like rubberslippers.

Rubber and plastic.Modern composite open heel fin.

Split decisions.Some of the newest fins have a split downthe center to reduce resistance by shapingthe blade much like a fish or whale’s tail.

Full Foot

Adjustable

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Preparation for Use. Full-foot fins generally requireno preparation, but you need to adjust adjustable-strap fins for a snug, comfortable fit. Do this withyour wet-suit boots on, of course. You may find newfin straps coated with a slick preservative. Wipe thisoff, otherwise your straps will tend to slip out ofadjustment.

Selection and Purchase. You buy your fins based onyour size, your physical ability and where you planto dive. If you’re looking at adjustable heel fins, you’llwant to have your wet suit boots for a proper fit.With the boots on, put your foot in the pocket. Thepocket should come to the point where your anklemeets your foot — if it won’t come up that high, youneed a larger size. Full foot fins should fit comfort-ably without binding, yet not feel loose. It helps towet your bare feet when trying on full foot fins. For agiven fin size, the larger and stiffer the blade, themore strength you need to use it.

Maintenance. As with your mask and snorkel, rinseyour fins in fresh water after use, store them in acool, dry place and keep them out of direct sunlight.Inspect fin straps regularly — they tend to wear outfaster than straps on other dive gear.

Although scuba diving has been around for morethan 50 years, it was in the last two decades thatthe equipment evolved into the effective, reliableand streamlined package you use today. You’regoing to find scuba equipment easy to use, reliable,comfortable and a joy to own.

Chapter One 37

1. Fins help you move more effec-tively by letting you use your legmuscles to swim.True False

2. What type of fin do you normallywear with wet suit boots?a. full foot finsb. wet suit finsc. adjustable strap fins

3. Which of the following are bladedesign features that enhance finperformance? (Check all thatapply):a. ventsb. vanesc. channelsd. ribs

4. To prepare new fins for use (checkall that apply):a. adjust the strap (for adjustablestrap)b. you don’t have to do anythingspecial (for full foot)c. None of the above.

5. Considerations affecting the finyou buy include (check all thatapply):a. your sizeb. your strengthc. where you plan to dive

How’d you do?1. True 2. c. 3. a, c, d. 4. a, b.5. a, b, c.


Performance andposh.Today’s diver can chooseequipment that’s sophist-icated and functional,and color-coordinatedand stylish, too, withcolors ranging from vividreds to muted blues,grays and black.

Fin foot fit.The fin pocket shouldcome to the point whereyour ankle meets yourfoot — if it won’t come upthat high, you need alarger size.

Full foot fin fit.Full foot fins should alsocome up to the pointwhere your ankle meetsyour foot. They should fitcomfortably withoutbinding, yet not feelloose.

Scuba Systems

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The modern scuba unit consists of three basic compo-nents: the BCD, the scuba tank (with valve) and theregulator. Let’s look at each, beginning with the BCD.

BCDsPurpose. As you read earlier, the aptly-named buoy-ancy control device, or BCD, is an expandable bladderthat you inflate or deflate to regulate your buoyancy.You can do this orally, using air from your lungs,though most of the time you’ll use a low pressure infla-tor, which inflates the BCD with air directly from yourtank. To decrease buoyancy, you deflate the BCDthrough a hose or valve.


Underline/highlight the answers tothese questions as you read:

38. Why does a diver need a BCD?

39. Why do divers need a back-pack?

40. Of the three styles of BCD,which is the most commonlyused by recreational divers?

41. What five features do BCDshave in common?

42. How do you prepare a BCD foruse?

43. What two special maintenanceprocedures apply to caring fora BCD?

MAINObjectives

Past and There are thremounted andby far most c

OWDM_013_043.qxd 2/23/06 11:54 AM Page 38

Besides allowing you to regulate your buoyancy under-water, the BCD provides positive buoyancy for resting,swimming or lending assistance to others. As youmight imagine, it’s considered standard equipmentmandatory for scuba diving.

Styles. There are three basic BCD styles: front-mounted, back-mounted and jacket-style. Of these,recreational divers by far most commonly use thejacket style. It wears like a sleeveless coat, holdingyour tank in place as well as providing buoyancy control.

It’s unusual to see a front-mounted BCD any more,although this is the original BCD design. It looks

present.e basic BCD styles: front-mounted, back-

jacket-style. Of these, recreational diversommonly use the jacket style.

somewhat like a life vest, worn over the head, andrequires a separate backpack for the tank.

Back-mounted BCDs are also relatively uncommon,though they’re still used in double tank diving. Somemodern BCDs fall somewhere between a back-mountand a jacket BCD, with jacket styling and features butmost of the BCD bladder behind you like a back-mount.Without arguing semantics, for our purposes we’ll treatthem as modern jacket style BCDs suited to recre-ational diving.

A related piece of equipment is the backpack, which inthe days of front-mounted BCDs you had to have as aseparate piece of gear. You need a backpack (again,obviously) to hold the tank on your back, but today thejacket BCD integrates the backpack into its design. Aswith front-mount BCDs, it’s very unusual to see sepa-rate backpacks today.

On your back.You need a backpack to hold thetank on your back, but today thejacket BCD integrates the backpackinto its design.

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Features — Regardless of the style, a BCD has five fea-tures necessary for scuba diving: First, it must holdenough air to give you and your equipment ample buoy-ancy at the surface. Second, it must have a large-diame-ter inflation/deflation hose, so you can release airquickly and easily. Third, it should have a low-pressureinflation system that fillsyour BCD with airdirectly from yourtank. Fourth, itmust have anover pressurerelief valveto preventthe BCDfrom ruptur-ing due tooverfilling ordue to air expan-sion during ascent.And finally, it should beadjustable enough (within your size) to fit comfortablyand not ride up on your body when you inflate it.

BCD features.

Low-PressureInflationMechanism

Proper Sizefor AmpleBuoyancy

ComfortableHarness andBackpack

Large DiameterInflation/Deflation Hose

OverpressureRelief Valve

Chapter One 39

Selection andPurchase. Virtuallyevery BCD on themarket has thesefeatures, so besidesfit and comfort,you’ll buy your BCDbased on other fea-tures. Try to choosea BCD that’s asstreamlined as pos-sible. Other desir-

able features include a utility pocket, a whistle forsurface communication, hose retainers and utilityrings for attaching accessory equipment. Manydivers like BCDs that include a weight system,which eliminates a separate weight belt (moreabout weight systems in Section 2). Your dive cen-ter, resort or instructor can help you find an appro-priate one.

Materials. Modern BCDs come in either double-bladder (or “bag”) or single-bladder designs. Thesingle-bladder design is usually made from acoated fabric that serves to both hold air and resist cuts, punctures and abrasions. Double-bladder BCDs consist of an inner bladder (usuallymade of urethane plastic), which holds the air, andan outer nylon shell that protects the inner blad-der from cuts, punctures and abrasions. Singlebladder types have become the most common.

Preparation for Use. BCDs require adjustment fora proper fit. If it’s too loose, it rotates awkwardlyaround you, and if it’s too tight, it can restrictbreathing, especially when you inflate it. Fortu-nately, most modern BCDs adjust easily — you canusually tighten or loosen them (to a degree) with-out taking them off.

With the BCD deflated, estimate the adjustment of the straps, lengthening or shortening them asneeded. Next, put it on (have someone help you if


1. You need a BCD to (check all thatapply):a. control your buoyancy underwater.b. provide positive buoyancy at the surface.c. keep your chest warm.

2. Of the three styles of BCD, the onerecreational divers use most commonly is:a. jacket styleb. back mountc. front mount

3. Which is not one of the five featuresa BCD needs to have?a. large diameter inflation/deflationhoseb. low pressure inflatorc. knife pocket

4. What additional maintenancerequirements do you have with aBCD? (Check all that apply).a. store deflatedb. rinse the interior with fresh waterc. store partially inflatedd. do not let water get inside the bladder

How’d you do?1. a, b. 2. a. 3. c. 4. b, c.


OWDM_013_043.qxd 2/23/06 11:54 AM Page 40

necessary) and fine-tune the adjustments until it fitssnugly, yet comfortably. Finally, inflate the BCD.Even fully inflated, it shouldn’t feel restrictive. Yourinstructor will help you adjust your BCD during yourconfined water dives.

Underline/highlight the answers to thesequestions as you read:

44. Why does a diver need a scuba tank?

45. What does a tank valve do?

46. With what piece of equipment is the backpack usually integrated?

47. What are the three common sizes and thetwo materials for scuba tanks?

48. What five markings do you commonlyfind on the neck of a scuba tank?

49. What are the two basic types of tankvalves?

50. What does a J-valve do, and why is its

MAINObjectives

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Maintenance. In addition to rinsing, drying and stor-ing it out of sunlight, your BCD has two additionalmaintenance considerations. First, you need to rinsethe inside as well as the outside with fresh water. Todo this, fill it about one third with water through theinflator hose, then the rest of the way with air. Swishthe water around the inside, then turn it upsidedown and drain it completely through the hose. Youmay have to reinflate with air a few times to get allthe water out. The second consideration is that youwant to store your BCD partially inflated. This keepsthe bladder from sticking together internally.

Some BCDs may have additional maintenancerequirements. Follow the recommendations in themanufacturer’s instructions.

Scuba Tanks and ValvesTanks and valves work together, so we’ll look at themtogether.

Purpose. Even a nondiver knows that a scuba tank isa cylindrical metal container used to safely storehigh-pressure air so you have something to breatheunderwater. Almost as obvious is the purpose of thetank valve, which is to control air flow from the tank.Sounds simple, but what you may not realize is thatthere are different types of tanks and valves to han-dle these two simple jobs.

Tank Styles and Features — Tanks come in a varietyof air capacities, depending upon their pressure rat-ing and size. In the metric system, you express tankcapacity in litres or kilograms of water capacity. Themost common sizes are 8, 10, 12 and 15 litres. In theimperial system, you express capacity in the numberof cubic feet of air you would have if you released it

Chapter One 41

use declining?

51. What’s the difference between a DIN valveand a yoke valve?

52. What is the purpose of a burst disc?

53. What three safety precautions for han-dling scuba tanks should you followgoing to and at a dive site?

54. How do you turn a tank valve on and off?

55. What’s the best way to keep water out ofa scuba tank?

56. Why do you need scuba tank visualinspections and pressure tests?

all at the surface. The three most commontank sizes are 50, 71.2 and 80 cubic feet,although other sizes are available.

The standard 12 litre/ 71.2- or 80-cubic-foottank contains about the same air you have ina walk-in closet, compressed into a spaceabout 600 mm/two feet long and 150 mm/halfa foot in diameter. As this air is compressedinto the tank, its pressure increases. Thepressure in scuba tanks may be higher than320 bar/4500 pounds per square inch (psi),but typical pressure ratings range from about170 to 200 bar, or 2250 and 3000 psi.

Tank Materials. Scuba tanks are either madeof aluminum or steel. Both types are subjectto regulations usually established by govern-ment agencies such as the U.S. Departmentof Transportation (DOT), Transport Canada(TC) and similar agencies in other countries.


OWDM_013_043.qxd 2/23/06 11:54 AM Page 42

Both steel and aluminum are equally accept-able materials, with different advantages and disadvantages. Aluminum holds upagainst corrosion in wet climates, whereassteel typically holds the same amount of airin a smaller tank at a lower pressure.

Among these regulations, scuba tanks mustpass periodic pressure tests (discussed below)mandated by these agencies.

The regulating agencies require tank manu-facturers to stamp specific information ontothe tank neck. These markings indicate thetype of material the tank is made of and themaximum pressure permitted in the tank(working pressure). Additional markingsinclude a serial number identifying the tank,dates of all pressure tests, and a manufac-turer or distributor symbol. These markingmay vary internationally.

Australian Aluminum Cylinders To As 1777 Specification Serial Number Water Capacity Working Pressure Test Pressure Tare Weight Date of Manufacture Logo Stamp Station No. Test Date

American Aluminum Cylinders Controlling Body(s) Specification Working Pressure (psi) Serial Number Makers Mark Date of Manufacture Logo Stamp Station No. Test Date

As 1777 Z216 wc 8.70 kg wp 20.7 Mpa at 15° CT 32 Mpa TW 11.15 kg 8.81

135 5.94

CTC/DOT- E6498-3000

P428829

10.81

135 5.94

Deciphered.Tank markingsindicate the tankmaterial, workingpressure, a serialnumber, dates of allpressure tests, andthe manufacturer ordistributor. Thesemarkings may varyinternationally.

Valve Types. Virtually all scuba tank valvesare made from chrome-plated brass.Historically, divers identified tank valves astwo basic types: the K-valve, which is a sim-ple on/off valve, and the J-valve, which has abuilt-in mechanism that signals when yourun low on air.

Without andwith reserve.K-valve and J-valve cylinders.J-valves are notused commonlyanymore in mostareas.

J-valve

K-valve

DIN-valve

The J-valve contains a spring-operated shutoffvalve that is held open by tank pressure untilthe pressure drops to approximately 20-40bar/300-500 psi. When the tank pressure dropsbelow that point, the pressure no longer holdsthe shutoff open, causing breathing resistanceto increase and warning that air is low.Pulling down the reserve lever releases theremaining “reserve” air. Although J-valveswere almost standard equipment in the 1960sbefore common use of submersible pressuregauges, today you see them much less fre-quently, and usually left in the nonreserveposition. An exception is in areas where regu-lations require them. They’re prone to acciden-tal tripping (so they don’t warn you), and theyincrease the cost and service requirements ofthe valve. The only reliable way to monitoryour tank pressure is to use a submersiblepressure gauge (SPG), which you’ll practiceusing during your confined water dives.

Without and with threads.By far the most common valve is the yokevalve (right); you attach the regulator via ayoke assembly. With the DIN valve system (left),you screw the regulator into the valve. Note thethreaded opening.

No O-ring, no diving.You find the O-ring mounted in the valve with theyoke system, and mounted in the regulator withthe DIN system. Either way, you can’t dive withoutthis O-ring — the regulator won’t seal — so learnto check for it when setting up your gear.

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Today, you can identify tank valves as yokevalves or DIN (Deutschees Institut fuer Normung)valves. By far the most common are yokevalves; as the name implies you attach theregulator via a yoke assembly. With the DINvalve system, you screw the regulator into thevalve. Although less common worldwide, theDIN valve system has the advantage of beingrated to higher working pressures. The DINsystem is very common in central Europe.

Valve Features: One thing to notice is that alltank valve connections with the regulatorrequire an O-ring, which makes an air tightseal. You find the O-ring mounted in the valvewith the yoke system, and mounted in the reg-ulator with the DIN system. Either way, youcan’t dive without this O-ring — the regulatorwon’t seal — so learn to check for it when set-ting up your gear.

Another feature you find in the valve is theburst disk. Burst disks relieve tank over pres-surization which can happen by accidentallyoverfilling the tank, or exposing it to excessheat. If the pressure gets too high, the burstdisk ruptures, releasing the air well before the tank would explode. In some countries,tank valves do not have burst disks.

Selection and Purchase. Selecting a tank andvalve depends, among other factors, on yoursize, the type of diving you will be doing, and

Chapter One 43

where you’ll use the tank. Consult your PADI Dive Center,Resort or Instructor for help when purchasing a tank foryour area.

Preparation for Use. Aside from assembling it with the restof your scuba gear, the only preparation required for a tankis having it filled at a reputable fill station, such as a divecenter. You’ll read about setting up your gear in theConfined Water Preview. Your tank will come with the valve installed, so you don’t have any preparation require-ments there.

Handling. Out of water, scuba tanks are heavy,unstable when left standing and tend to roll whenlying down. The cylindrical shape has a purpose –it’s structurally very strong and one of the bestshapes for containing pressure.


Stay put! When carrying your tanks in yourautomobile, lay them downhorizontally and block or tie themso they can’t slide or roll.

Formorein

formationabout...


OWDM_044_074.qxd 2/23/06 11:56 AM Page 44

To avoid damaging your tanks, or having yourtanks damage something else or even hurt some-one, always block or secure them so they can’t roll.Don’t leave them standing unattended, because

they fall over easily, which can damage your BCD or regula-tor if you’ve set up your unit. If you need to leave tanksstanding up — which is common to save deck space on aboat — you need to secure them so they can’t fall. Diveboats commonly have special racks for this. When carryingyour tanks in your car, lay them down horizontally andblock or tie them.

Maintenance. Besides rinsing your tank and valve withfresh water and storing it out of the sun, you have someextra considerations for care.

Your tank valve should operate easily and smoothly. If thereis any difficulty in operation, don’t try to lubricate it. Have aprofessional dive operation service it. Closing a valve tootightly can damage its high-pressure seal. When setting upyour equipment, open the valve slowly, all the way until itstops turning.(Note: It used to be common to open the valveall the way, and then close it a quarter to half a turn. Thisisn’t necessary with modern valves, though it doesn’t hurtanything if someone does it.) When you’re taking it apart,

close it all the way gently. Always close valves gently andavoid over-tightening.

Although you have several consicare of your scuba equipment, yor Resort makes life easy: Apartdrying and storing properly, theytative maintenance and repair soto twenty different places. Look tCenter or Resort for:

• Regulator overhauls and adjus• Quality air fills• Tank visual inspections• Hydrostatic tests• Gauge accuracy checks and c• Routine adjustments, problem

One StoOne Sto

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Your dive operation fills your tank with totally dry airbecause moisture inside can cause rust or corrosion on itsinner surface. It is also important to keep water out of yourtank. The best way to do this is to never allow it to com-pletely empty. If you do empty the tank completely, close thevalve immediately to keep moisture out. Water can evenenter an empty tank by backing up through a regulator, sohaving the regulator attached doesn’t guarantee a dry inte-rior. Also, bleeding the air from your tank quickly can causeinternal condensation and corrosion.

In recreational diving, scuba tanks should only be filledwith compressed air for breathing — never pure oxygen.During filling, your dive operation will usually cool yourcylinder in water (it heats as the pressure rises). Tanksshould only be filled to the rated pressure, since overfillingcan lead to metal fatigue and shorten the life of the tank.

Chapter One 45

Diver’s home away from home.Look to your PADI Dive Center or Resort forthe specialized expertise you need for longterm equipment maintenance and periodicrepair.

derations for takingour PADI Dive Center from rinsing after use, can complete preven- you don’t have to treko your PADI Dive

tment

alibration diagnosis and repair.

p Equipment Carep Equipment Care

Your tank may have a rubber or plastic boot, which allowsthe tank to stand (where appropriate) and creates someprotection if it bumps into things. Check underneath the


Inside information.To check for internal rustand corrosion, you need tohave a professional visuallyinspect the inside of yourtank at least once a year.

OWDM_044_074.qxd 2/23/06 11:56 AM Page 46

boot periodically for corrosion. To check for internal rustand corrosion, you need to have a professional visuallyinspect the inside at least once a year. To do this, theinspector drains the tank slowly and removes the valve.Using a special inspection light, the inspector checks forcorrosion, cracks, debris and other possible damage. (Thisservice must only be performed by a trained professionalat a qualified service center — do not empty the tankyourself.) Once the tank passes the visual inspection, theinspector usually puts a sticker with the test date on thecylinder (they’re not used in all areas). Professional divefacilities will not fill a tank without a current visualinspection sticker.

Because tanks are also subject to metal fatigue, they mustreceive periodic pressure tests called hydrostatic tests. Thetest subjects the cylinder to very high pressure in a spe-

cial testing tank, and evaluates how much itexpands and contracts, which reveals metalfatigue or stress. When a tank passes the hydro-static test, signifying that it can safely hold airat its rated pressure, the tester stamps the testdate onto it. Professional dive facilities will notfill a tank lacking a current hydrostatic testdate. Your instructor will tell you what local ornational standards relate to your cylinder hydro-static testing. Standards vary from country tocountry; for example in the United States andCanada, you need to have your tank hydrostati-cally tested every five years. In central Europe,steel tanks require hydrostatic testing every twoyears, and aluminum require it every five years.

You also need to store your tanks properly. Keep them in acool place, especially when full, because the pressure ofcompressed air rises when exposed to heat. Full scubatanks left in a hot environment, for example, can rupturethe valves’ burst discs. Store tanks with between 10-20bar/100-300 psi of air to keep moisture out. If you store atank without using it longer than six months, have the

tank refilled since the air inside can turn stale. Differenttypes of cylinders may have other maintenance consider-ations that you’ll want to follow according to the manu-facturer’s instructions.

With proper handling and maintenance, a scuba tankand valve can last many years. And you can buy tanks ina wide variety of colors, including some with patternsand pictures.

Chapter One 47

1. The two metals scuba tanks are commonlymade from are:a. aluminum and copper.b. aluminum and steel.c. copper and steel.

2. The circled markingon the tank is:a. the hydrostatic testdate.b. the working pressure.c. the serial number.

3. A ________ valve is an on-off valve, and a _________ valve has a built inreserve.a. K, DINb. K, yokec. J, Kd. K, J

4. You connect a regulator to a ________ byscrewing it into the valve.a. yokeb. DINc. None of the above.

5. A burst disc:a. relieves pressure from an overfilled orheated tank.b. is required for your regulator to seal tothe valve.c. None of the above.

6. When transporting tanks (check all thatapply):a. block them so they can’t roll or fall.b. don’t leave them standing unattended.c. if they must be left standing, secure themso they can’t fall.

7. To keep water from entering a tank:a. don’t let it drain of air completely.b. always close the valves very tightly.c. All of the above.

8. You need an annual visual inspection to:a. check the quality of air in the tank.b. check for internal corrosion.c. All of the above.

How’d you do?1. b. 2. a. 3. d. 4. b. 5. a. 6. a, b, c. 7. a. 8. b.


XXX

8.94

1234

XXXXXX WC 8.6 kg

T32 MPa *9/87

F 20.7 MPa

8.94

OWDM_044_074.qxd 2/23/06 11:56 AM Page 47

RegulatorsPurpose. Your regulator makes it possible to use the air inyour tank. It reduces the scuba tank’s high pressure air tomatch the surrounding water pressure, and it delivers aironly on demand, when you inhale. It regulates the air flow,hence the name “regulator.” Technically, it’s a highly sophisti-cated demand valve, so in some areas divers prefer “demandvalve” to “regulator.”



57. What does a regulator do?

58. When looking at a regulator,which are the following parts:• first stage?• second stages?• dust cover? • purge button?

59. What’s the most importantfeature for consideration whenpurchasing a regulator?

60. How do you rinse a regulatorafter use, and what threepoints do you need to keep inmind while doing so?

MAINObjectives

Less is more.The modern scuba regulator is asimple and reliable device withonly a few moving parts.

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Styles and Features. The modern scuba regulator is a simpleand reliable device with only a few moving parts. It has twostages: a first stage, which you attach to the scuba tank valveand a second stage that has a mouthpiece. The stages reducehigh-pressure air from the scuba tank sequentially. The firststage reduces the high tank pressure to an intermediate pres-sure of 7-10 bar/100 to 150 psi above the surrounding waterpressure. The second stage reduces this intermediate pres-sure to the water pressure surrounding you, which is whatyou need for comfortable breathing. Easy breathing is themost important feature of a regulator.

Regardless of make, all modern regulators share a relativelysimilar basic structure. Familiarization with regulator termi-nology and how it functions will help you understand furtherexplanations regarding regulators.

Look at the regulator second stage diagram. Thesecond stage is basically a cup or air space coveredwith a flexible diaphragm (usually silicone rubber),a lever-operated inlet valve, a mouthpiece and anexhaust valve. When you inhale, you pull thediaphragm inward, which pushes the inlet valvelever to release air. When you stop inhaling, airpressure inside the second stage rises, and thediaphragm returns to its relaxed position, releasingthe lever and allowing the valve to close. The purgebutton lets you manually control the flow of air bydepressing the diaphragm and valve lever.

When you exhale, the exhaust valve opens and the air ventsout through the one-way exhaust valve. The exhaust valveremains closed when you’re not exhaling, keeping water outof the regulator.

The alternate air source simanother diver, should the nesource usually has a longeryou can find it easily. You’llnate air sources in Section Tget practice using one durindive.

Besides these, your regulatopling device at the to the low-pressureyou’re using a dry sthe longer one gene

Materials. Althoughturers of popular retors are made fromThe first stage is geplated brass, thougmodels made from may be made from a combination of boand exhaust tees atic, neoprene and s

MovableLever

PurgeButton

FlexibleDiaphragm

Air from Tank

InletValveOpen

InletValve

InletValveClosed

Mouthpiece

ExhaustValve

ExhaustValveClosed

ExhaustValveOpen

Inhale Exhale

STATIC DIVER INHALES DIVER EXHALES

How it works.The second stage is basically a cup covered with a flexible diaphragm, a lever-operatedinlet valve, a mouthpiece and an exhaust valve. When you inhale, you pull the diaphragminward, which pushes the inlet valve lever to release air. When you stop inhaling, airpressure inside the second stage rises, and the diaphragm returns to its relaxedposition, releasing the lever and allowing the valve to close. When you exhale, theexhaust valve opens and the air vents out through the one-way exhaust valve.

Alternate AirSourcePurge Button

First StagePressureGauge

Formorein

formationabout...


SecondStage

OWDM_044_074.qxd 2/23/06 11:56 AM Page 49

The regulator you use dur-ing confined-water trainingwill have several attach-ments. The first of these is asubmersible pressure gauge(SPG), which shows you howmuch air you have (dis-cussed in detail shortly).Your SPG may be part ofyour dive computer, whichyou’ll learn more about inSections Two, Four and Five.Your regulator will also havean extra second stage calledan alternate air source. (Thealternate air source may alsobe part of your BCD infla-tion/deflation hose.)

plifies sharing air withed arise. The alternate air

hose and a bright color so pick up more detail on alter-

wo of this manual, and you’llg your first confined water

r will have a hose with a cou-free end. This hose connects inflator on your BCD. Ifuit, you’ll have two of these;rally goes to your dry suit.

there are several manufac-gulators, virtually all regula- the same basic materials.nerally made from chrome-

h there are a few high endtitanium. The second stagebrass, high-impact plastics orth. Parts like mouthpieces

re generally made from plas-ilicone rubber.

Chapter One 49

Selection and Purchase. As mentioned, you want to choose aregulator based on ease of breathing. With your PADI DiveCenter’s help, you can choose an easy-breathing regulator bycomparing flow rates and breathing resistance. Virtually allmodern regulators perform well within recreational diving lim-its, so you’ll be choosing based on the feel you prefer, takinginto consideration things like service availability and so on. Ofcourse, you can usually purchase a suitable regulator thatmatches thFe style of your mask, fins, snorkel, BCD and tank.

When buying your regulator, you’ll want to get your alternateair source at the same time. Again, have your PADI Resort,Instructor or Dive Center assist with your selection.

Preparation. Aside from assembling of your scuba unit, yourregulator requires no special preparation other than theattachment of accessories. Leave attaching accessories to thetrained professionals at your dive center or resort— they usu-ally take care of this when you purchase your regulator.


Take care of it, it takescare of you.During rinsing, flush fresh waterthrough any holes in the firststage (except the high-pressureinlet covered by the dust cap, ofcourse) and through the secondstage mouthpiece. Keep the firststage higher than the second tominimize the possibility that waterwill flow up the hose to it.

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Maintenance. After each use, rinse your regulator with therest of your equipment. It’s often best to soak it, while stillattached to your scuba tank, then rinse it with running water.If rinsing your regulator after it’s been removed from yourtank, keep these points in mind:

1) Put the first stage dust cover firmly in place to keep waterout of the first stage.

2) Do not use high-pressure water to rinse your regulator —only gently flowing water.

3) Don’t press the purge button while rinsing or soaking,because this opens the second stage inlet valve and can allowwater to flow up the hose into the first stage.

You may prefer to rinse your regulator while attached to yourtank with the valve open. By doing this, there’s no way waterwill accidentally enter the valve and first stage. During rins-ing, flush fresh water through any holes in the first stage(except the high-pressure inlet covered by the dust cap, ofcourse) and through the second stage mouthpiece. Keep thefirst stage higher than the second to minimize the possibilitythat water will flow up the hose to it. It’s a good precaution toattach the regulator to the scuba tank after rinsing and to

Chapter One 51

As you learn about scuba equipment function and use, you quickly learnthat nothing you use works in isolation. Much equipment has little utilitywithout other equipment that integrates with it. So as you invest in yourown equipment, select integrated packages rather than buying items in isolation.

Your PADI Dive Center or Resort can guide you in purchasing equip-ment packages that integrate well together. They may even have popularequipment prepackaged with this in mind.

Here’s a list of integrated equipment packages, along with accessories.Notice that because integration overlaps, some items appear in morethan one package. Don’t look at thesepackages as isolated systemsbecause they’re not. Rather, chooseequipment based on the type of divingyou plan with it, and the way it workswith other equipment you have or willhave. This gets you kitted up with gearthat works well together. Of course,you can look to your PADI Dive Centeror Instructor for advice as well.

1. Mask, fins and snorkel. You canhave a lot of fun with just these,and it doesn’t make much sense tohave any two and not the third.Don’t forget mask defog, wet suit boots for open heel fins, sparestraps and a mesh carrying bag.

2. Regulator, alternate air source, submersible pressure gauge, BCD,weight system, cylinder. This makes up your “scuba unit.” If you planto travel by air for most of your diving, the cylinder may be optional.Don’t forget an equipment bag, hose protectors, clips and parapher-nalia for rigging, spare o-rings, etc.

3. Exposure suit, exposure suit accessories, BCD, weight system. TheBCD appears in this list because if you’re looking at cooler water div-ing, you may need to integrate your exposure suit (dry) with theappropriate BCD. Don’t forget a mesh bag for carrying a wet expo-sure suit, suit repair cement, wet suit detergent, and plastic hangersfor drying/storing.

4. Dive computer, SPG, compass. You may opt for an instrument con-sole or independent (wrist mount) gauges, but think in terms of thedata: depth, time, direction, air supply. It’s a good idea to look atthese along with package #2. Don’t forget gauge face protectors, clipsand rigging accessories, spare batteries and padded cases.

Scuba EquipmentThe Integrated Approach to Buying

Greater than the sum of the parts.When purchasing equipment, think interms of integrated packages rather thanisolated pieces.

OWDM_044_074.qxd 2/23/06 11:56 AM Page 51

purge the regulator briefly to blow out any water thatmay have entered the first stage accidentally.

Keep your regulator free of sand, mud and debris. Toprevent damage to the hoses when storing or packingyour regulator, allow the hoses to form large, gentlecurves rather than tight loops. Don’t use hoses to pullor handle your scuba unit (they’re strong, but they’renot that strong). It’s better to store your regulatorlying flat than to hang it by one of the stages or hoses.

Your regulator requires periodic lubrication andadjustment, not to mention inspection, to assure thatit operates reliably. So, an important part of regulatormaintenance includes professional servicing at leastonce a year, or sooner if it begins to breathe hard orleak air, or according to manufacturer specifications.With proper maintenance and with annual servicing,your regulator should provide many years of depend-able service.

52

1. A regulator reduces high pressuretank air in four steps.True False

2. The part of the regulator in the photo is:a. first stageb. second stagec. low pressure hose

3. When rinsing your regulator, remem-ber to:a. put the first stage dust cover inplace.b. not depress the purge button.c. use gently flowing water.d. All of the above.

How’d you do?1. False. It reduces it in two steps.2. b. 3. d.


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Submersible Pressure GaugePurpose. The submersible pressure gauge (SPG— sometimes called the “contents gauge”) tellsyou how much air you have during a dive, in much thesame way that an auto’s fuel gauge tells you howmuch fuel you have. You’ll learn to use your SPG toplan and control your dive so you return safely to theboat or shore without running out of air. Since youdon’t want to run out of air underwater, as you mightexpect, the SPG is mandatory equipment.

A point to remember is that your SPG is a passivedevice. You have to read it, or it doesn’t do you anygood. Develop the habit of checking your submersiblepressure gauge frequently while diving. With practiceyou’ll get a feel for how fast you use air and won’tneed to check quite as much, but for now check it allthe time. Better too much than too little.

Styles, Features, Materials. Although SPGs all havethe same purpose, there are a few basic styles andfeatures. These range from gauges that simply tell you

Open Water Diver Manual

Underline/highlight the answer to thisquestion as you read:

61. Why do divers need a submersiblepressure gauge?

MAINObjectives

your air pressure, to electronic gauges that incorporateother instruments (dive computers). Some of the newestmodels have no hose, but use a transmitter mounted onthe first stage to send air supply data to a computer onyour wrist.

Selection and Purchase. Have your PADI Dive Center,Resort or Instructor help you select the best SPG whenyou invest in your regulator. Since it’s mandatory equip-ment, it makes sense to purchase an SPG along with the regulator.

Preparation. The only preparation required is to haveyour dive center or resort attach the SPG (or transmitter,if it’s the hoseless type) to your regulator.

Maintenance. Whether a simple gauge or part of a com-puter, your SPG is a precision instrument that requirescareful handling. Do not drop or bang it, and be careful toavoid lying a tank or other heavy object on top of it. Whilediving, don’t let it drag or dangle, which not only damagesthe SPG, but can damage fragile aquatic life.

Because the SPG (or transmitter) remainsattached to your regulator, simply rinsing andsoaking it along with the regulator takes care ofits maintenance. When you take your regulator infor annual servicing, be sure to have your diveprofessional take care of your SPG as part of the servicing.

Equipment IdentificationIt’s a good idea to mark your equipment for easyidentification using special diving equipmentmarkers. These may be marking paint, crayons orcolored tape, among others. After you’ve investedin matching mask, fins, snorkel, etc., it’s a good idea tomark your gear where it’s not visible when you’re wearingit, but is when you’re not — such as putting your initialsinside the fin foot pocket.

Marking your equipment prevents frustration and confu-sion when you’re around other divers using similar equip-

Chapter One 53

Nice to know.The submersible pressure gauge (SPG —sometimes called the “contents gauge”) tellsyou how much air you have during a dive.

1. The SPG (submersible pressure gauge) ismandatory equipment on all scuba dives.True False

How’d you do?1. True.


OWDM_044_074.qxd 2/23/06 11:56 AM Page 53

ment, adjusted to different sizes. This happens a lot on diveboats, and there may be others with similar gear in yourconfined water dives.

During your confined water dives, you’ll start practicingthe buddy system — always diving with a buddy who staysnearby at all times. Your buddy assists you with things likeputting on and checking your equipment before the dive,helps remind you to check your depth, time and air supplylimits, and provides emergency assistance in the unlikelyevent you need it. Hopefully it goes without saying thatyou do the same for your buddy. With a proper buddy system, you both benefit in terms of convenience, safetyand fun.

Diving is a social activity, so the buddy system is morethan one of diving’s safety rules — though it is that. Divingwith someone adds to the fun. Together, you and yourbuddy share experiences and underwater adventures,sometimes seeing things that no one else ever will. Youmay be surprised how many new friends you meet through

The Buddy System


Underline/highlight the answer to thisquestion as you read:

62. What are three reasons for divingwith a buddy at all times?

MAINObjectives

That’s what friends are for.Diving with someone adds to the fun, andit’s important for safety. Together, you andyour buddy share experiences and under-water adventures, sometimes seeing thingsthat no one else ever will. You may besurprised how many new friends you meetthrough diving and the buddy system.

OWDM_044_074.qxd 2/23/06 11:56 AM Page 54

diving and the buddy system. Three general reasons applyto diving with a buddy: 1) practicality, 2) safety and 3) fun.

You and your buddyhave a responsibil-ity to each other.For the buddy sys-tem to work, youand your buddymust take it seri-ously (but still havefun) and work atstaying togetherunderwater. So,develop the habitand start practicingthe buddy systemduring your con-fined water dives.

1. Reasons for diving with a buddyinclude (check all that apply):a. practicalityb. safetyc. fun

How’d you do?1. a, b, c.


Okay, now you’re about ready to go diving in the pool or confined water. If you’ve never doneit before, you’ll find it exhilarating breathingunderwater for the first time. You’ll never forget it.

During your first confined water dive, yourinstructor and the instructor’s assistants willhelp you set up your gear, put it on and takeyou through the steps of going underwater withscuba for the first time. Then, you’ll start learn-ing and practicing some of the skills you’ll needas a diver.

Your instructor will be at hand the whole time,guiding you and making sure you have funlearning to dive. If you have a question or wantsome assistance, ask. The PADI Open WaterDiver course enables you to meet physical andacademic performance requirements through avariety of adaptive techniques. And as it said inthe introduction, if you don’t understand whyyou’re doing something, find out. After all, itdoesn’t matter if you can do something perfectlyif you don’t know when and why you would do it.

Your instructor willgo over each of thefollowing scubaskills, and maypresent them in aslightly differentorder or manner toaccommodate logis-tics, your individ-ual needs, localconditions and soon. But this willgive you an idea ofwhat you’re goingto be doing.

Chapter One 55

In these subsections on Dive Equipment andthe Buddy System, you learned that:

▲ Comfort and fit are the two most impor-tant criteria in purchasing dive gear.

▲ You can’t use goggles for scuba divingbecause they don’t enclose your nose.

▲ You need to rinse your equipment infresh water after each use.

▲ The jacket BCD is by far the most com-mon BCD used by recreational divers.

▲ Your scuba tank needs an annual visualinspection, and periodic pressure (hydro-static) testing.

▲ You never leave scuba tanks standingunattended. You block/secure them whentransporting so they can’t fall or roll.

▲ Regulators reduce tank pressure in twostages to breathing pressure.

▲ A regulator’s most important feature isease of breathing.

▲ You need to have your regulator profes-sionally serviced annually.

▲ Have the dust cap in place and don’tpush the purge button when you rinseyour regulator.

▲ You need an SPG (submersible pressureor contents gauge) so you can tell howmuch air you have at any time during the dive.

▲ You always dive with a buddy for safety,practicality and fun.

▲ You can make all your dive gear matchand look good without sacrificing comfort,fit or important features.

Summary PointsSummary Points Confined Water Dive Preview

WOW! If you’ve never done it before, you’llfind it exhilarating breathing under-water for the first time. You’ll neverforget the first time you use scuba.

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Here’s what you’ll be able to do when yousuccessfully complete Confined Water Dive One:

1. Don and adjust mask, fins, snorkel,BCD, scuba and weights with the assis-tance of a buddy, instructor or certifiedassistant.

2. Inflate/deflate a BCD at the surfaceusing the low pressure inflator.

3. In water shallow enough to stand in,demonstrate proper compressed-airbreathing habits, remembering tobreathe naturally and not hold thebreath.

4. Clear a regulator while underwater byexhalation and purge-button methods,and resume breathing from it.

5. In water shallow enough to stand in,recover a regulator hose from behindthe shoulder while underwater.

6. In water shallow enough to stand in,clear a partially flooded mask whileunder water.

7. Swim underwater with scuba equipmentwhile maintaining control of both direc-tion and depth, properly equalizing theears and mask to accommodate depthchanges.

8. While underwater, locate and read thesubmersible pressure gauge and signalwhether the air supply is adequate orlow based on the gauge’s caution zone.

9. In water shallow enough to stand in,breathe underwater for at least 30 sec-onds from an alternate air source sup-plied by another diver.

10. While underwater, recognize and/ordemonstrate standard hand signals.

11. Demonstrate the techniques for aproper ascent.

Confined Water Dive One

Skill Requirements

Skill Requirements

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Assembling Your Scuba EquipmentBefore you can use scuba equipment, you have to put yourtank, regulator and BCD together. Your instructor may haveyour gear already set up for this first confined water dive,or may guide you in putting it together. Between now andwhen you finish the course, you’ll have put it together andtaken it apart until it’s second nature.

Put the BCD on the tank. If you bought a brand new BCD,wet the nylon tank band. You do this because new nylonstretches when wet; if you attach the band dry, it mayloosen when you get in the water. Now:

1. Slide the BCD onto the standing tank from the top.

2. Turn the tank so the valve opening faces toward theBCD, where your head will be. For most BCDs, you wantthe top of the hard plate in the jacket (if it has one) or thecollar to be about even with the base of the tank valve. Yourinstructor can help you with this, and you may go higher orlower to suit your preference after using your gear a bit.

3. Secure the tank band by tightening it as far as you canby hand, then swinging over the locking mechanism. Itshould take a bit of strength. Locking mechanisms vary, sohave your instructor show you how yours works if it’s notobvious (it often isn’t). Some BCDs use two tank bands;tighten and secure both.

4. Now check that it’s secure. See if the band slides up anddown on the tank. If not, you can lift the tank off theground slightly holding the top of the BCD backpack, andgive it a little shake. If the BCD doesn’t shake or slide onthe cylinder, good job. If it moves, you’re too loose. Readjustthe band for a tighter fit.

Attach the regulator. If the regulator’s out of reach, lay thetank and BCD down, with the BCD up, before you go get it.

1. The tank valve opening may be covered by a piece of tapeor a plastic cap. If so, remove the tape or cap (discard tapeproperly — please do not litter).

Chapter One 57

Right height.For most BCDs, you want the top of thehard plate in the jacket (if it has one) orthe collar to be about even with the baseof the tank valve. Your instructor can helpyou with this, and you may go higher orlower to suit your preference after usingyour gear a bit.

Swing and lock.Secure the tank band by tightening it as faras you can by hand, then swinging overthe locking mechanism. It should take a bitof strength.

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2. Check the valve opening for an O-ring (yoke system —for DIN, check the regulator first stage connection). Itshould be clean and free from cuts or nicks. If you need anew O-ring, see your instructor.

3. Open the tank valve slowly — just for a burst — toblow any accumulated water or dirt from the valve open-ing. Aim it away from people. If you’re certain there’s nowater or debris, you can skip this step.

4. Remove the regulator dust cap by loosening the yokescrew (yoke system) or unscrewing (DIN system).

5. With the tank between your legs and the BCD awayfrom you, put the first stage on the tank valve so that thevalve opening meets the first stage opening, and so thesecond stage hose leads to the right. The primary secondstage hose goes over your right shoulder.

6. Tighten the yoke screw until it is just finger tight, or forDIN equipment, gently screw in the regulator until it issnug.

7. Attach the low pressure hose from the regulator to theBCD low-pressure inflator.

Turn on the air and check its operation. You should nowbe ready to turn on the air. Hold the SPG in your lefthand away from you, facing away, as you turn it on — thisis a precaution in the unlikely event the SPG leaks inter-nally and the face bursts; modern SPGs have blow outplugs so this isn’t likely to happen even if it does have aleak. Play it safe anyway.

Open the valve slowly and gently. If you hear a small leak,the O-ring may be dirty or defective. Close the valve andask your instructor to show you how to inspect andreplace it. Assuming no leaks, open the valve all the way.

Check your air with the submersible pressure gauge. Lookat the working pressure on the tank and compare it to theSPG, and you’ll have an idea how full the tank is. You’llquickly learn the full pressure for most tanks in your area.


Put it together.Position the regulator so the primary second stagecomes off to the right. Tighten the yoke screwfinger tight, or for DIN equipment, gently screw inthe regulator until it is snug. Attach the lowpressure hose to the BCD inflator.

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Next, test the regulator by pressing the purge buttonmomentarily. The air should flow freely and stop whenyou release the button. A slight hissing from the secondstage may stop if the purge button is pressed or themouthpiece opening is blocked momentarily. If it does not,notify your instructor. Some very sensitive regulatorsmay begin to free flow (release air continuously) loudlywhen you press the purge; put your fingers across themouthpiece and it should stop.

Check the exhaust valve by exhaling into the regulator.Exhalation should be easy. If not, the exhaust valve maybe stuck — notify your instructor. If both the purge andexhaust valves function properly, take a few breaths fromthe regulator as a final check. The regulator shouldbreathe easily and smoothly.

Secure hoses and streamline your gear.Dangling SPGs and alternate air sourcesdamage themselves as they drag on the bot-tom and the reef. They create drag while you swim andthey can destroy and kill sensitive aquatic life.

Your BCD and hoses will have clips, snaps and otherattachments so that none of your hoses dangle. Ideally,when swimming underwater nothing hangs below yourbody line more than about 20 cm/8 inches — and less isbetter. Typically, you run the SPG hose under your leftarm and attach it to the front of your BCD where you caneither see it, or easily swing it up and see it. Your alter-nate air source usually runs under your right arm(though this may vary with the type) and attaches in thetriangle formed by your chin and the corners of your ribcages. You’ll use a clip or holder that holds it securely, butreleases with a firm tug.

Your instructor will help you secure hoses and streamlineyour gear. When you’re done, remember to lay it downcarefully, BCD up, with the second stage on top so it staysout of the sand or dirt.

Adjustments and Gearing UpYou’ll probably prepare and adjust your mask, snorkel

Chapter One 59

Face away.While holding the SPG away from you, openthe valve all the way gently.

Breath of fresh air.If both the purge and exhaust valvesfunction properly, take a few breaths fromthe regulator as a final check. The regulatorshould breathe easily and smoothly.

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http://www.projectaware.org/

and fins before you come to your first confined water dive.Let’s look at your other gear, much of which for this first diveyou’ll probably put on in shallow water. Your instructor willguide you through the steps for gearing up.

Adjusting your BCD. As you read earlier, adjust theBCD jacket to feel snug and comfortable. This mayrequire tightening or loosening the shoulder strapsand the waist straps. If you’re wearing the right sizeBCD, you can probably make these adjustments afteryou put your scuba unit on.

With your own equipment, you’ll make many initialadjustments that you won’t have to change. Each timeyou gear up, your equipment is already set for yourcomfort.

Adjusting the weight belt. If you’re using a weightbelt, your instructor will tell you approximately howmuch weight to use. Distribute the weights evenly on

the belt and adjust the belt length to be no more than 15 to20 cm/6 to 8 in longer than needed to fit your waist. (You willlearn more about weight belts and weight systems in SectionTwo.) Now it’s ready to put on.

Wet Suit. You may wear a wet suitjacket, vest, or an entire wet suit dur-ing your confined-water dives. Thisgets you used to using it before you gointo open water.

If you’re wearing a full wet suit, you’llput the pants on first. Wet suits haveto fit snugly, so expect some effortdoing this — it gets easier with prac-tice.

After you get the pants on, wet suitboots come next. Tuck them under thewet suit pants cuff. Put on a wet suitjacket one arm at a time. Work thesleeve all the way up to your arm pitbefore starting on your other arm.


Don’t be a drag.Use clips, snaps and otherattachments on your BCD sothat none of your hoses oraccessories dangle. Ideally,when swimming underwaternothing hangs below yourbody line more than about20 cm/8 inches — and less isbetter.

Snug = warm.Wet suits have to fit snugly, so expectsome effort in pulling one on — it getseasier with practice.

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With a proper fit, the suit should feel snug and somewhatrestrictive. The restriction eases in the water, and after wear-ing a wet suit a bit, you’ll get used to how it feels.

If you don’t use a wet suit jacket or vest duringthis dive, it’s a good idea to wear a body suit, orat least a T-shirt or sweatshirt (with a catchylogo on it) to reduce any chaffing.

Weight belt. Whether you put on a weight beltbefore or after your scuba unit depends on theBCD — usually it goes on first. If you’re using aweight integrated BCD, this isn’t an issue at all.

Regardless of when you put on the weight belt,you must be able to remove it quickly and easily, so it mustremain free and clear of all other equipment. Your instructorwill help you do this.

To put on a weight belt before entering the water, hold thebuckle end in your left hand and the free end in your right.Step over it and then bend forward, laying the belt across thesmall of your back. By donning the belt in this manner, youtake the strain off the front so you can position the belt andsecure the buckle.

Be sure you wear the weight belt so that it has a right handrelease. This is a standard release position. Generally, if youhave the buckle on the left side, the release opens to the right.Note that you set the weight belt release and the scuba unitreleases to open in opposite directions to help prevent confu-sion. Loosen and secure the weight belt release without look-ing. Underwater, with a mask and BCD on it’s difficult to seeyour waist, so you’ll want to be sure you can operate theweight belt by touch.

Finally, try to distribute the weights evenly so they don’t inter-fere with the quick-release buckle. It also helps to have themslightly forward to make you more stable when swimming,with a gap in the center of your back where the tank lies.

Scuba Unit. Before putting on the scuba unit, first make sureyou connect the BCD shoulder releases (if present) and that

Chapter One 61

Left gets it right.Be sure you wear the weightbelt so that it has a righthand release. This is astandard release position.Generally, if you have thebuckle on the left side, therelease opens to the right.

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you’ve unfastened the waist belt. The easiest way to putyour scuba unit on is to have your buddy hold it while youslip into it like a coat. Before your buddy lets go, putting itsweight on you, straighten any twisted straps and make sure

you’re not trapping any hoses or accessoriesinside the jacket. After setting the unit onyou, your buddy can help you find the waistbelt on each side.

Next, bend forward and balance the tank onyour back to take the strain off the harness. Itis easier to adjust and secure the unit in thisposition than when standing upright. Checkto be sure that the waist belt release opens tothe left.

After everything feels secure, stand upright and tilt yourhead back. If your head can touch the valve, the tank isprobably too high. You don’t want it hitting your head, sotake the unit off and readjust the BCD height on the cylinder.

Mask. Condensation will fog the inside of your mask unlessyou use defog. It’s best to use commercial defog, thoughsaliva will work if none is available. Rub defog on the insideof your mask lens and rinse it once, briefly.

Now you’re ready to put yourmask on. Hold it on your facewith one hand while pulling thestrap into place with the other.Develop the habit of keeping yourmask on your face wheneveryou’re in the water.

Fins. You usually put fins on last,as close to the water — or even inthe water when appropriate —as possible. Walking in fins isclumsy at best, and can be haz-ardous. If you must walk withfins (whether in or out of thewater), shuffle your feet and walk backwards, looking overyour shoulder to see where you’re going.


Take a load off.The easiest way to put yourscuba unit on is to haveyour buddy hold it while youslip into it like a coat. Beforeyour buddy lets go, puttingits weight on you, straightenany twisted straps and makesure you’re not trapping anyhoses or accessories insidethe jacket.

Proper application.To put on your mask, hold it on your face withone hand while pulling the strap into placewith the other.

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Wet your feet (or boots) and fins to make them eas-ier to don. Have your buddy steady you as you puton one fin at a time. Work your foot well into thefoot pocket before pulling on the strap (adjustablestrap) or pulling up the heel portion (full foot).

Inspect your equipment. Develop the habit ofinspecting your and your buddy’s equipment for

correct positioning, adjust-ment and function beforeentering the water. Youshould be familiar with whereto find and how to work eachother’s BCD controls andreleases. During your secondconfined water dive, you’lllearn how to do this with afive step predive safety check.

Inflating and Deflating Your BCDNow you’re ready to practicesome dive skills. You want toknow how to inflate yourBCD at the surface so thatyou can remainupright and

rest, talk, listen or adjust equipment withouthaving to tread water. An inflated BCD alsoprovides support while swimming at the sur-face. Whenever you’re at the surface, youshould have your BCD partially inflated.

You can inflate your BCD two ways: orally and through the low-pressure inflator mecha-nism connected to your regulator. You’ll learnto inflate it orally in your next confined water dive.

To inflate the BCD using the low-pressureinflator mechanism, press the inflation button(not the same one you used to orally inflate).Put air in your BCD in short bursts, so you

Chapter One 63

Backward is forward.Walking in fins is clumsyat best, and can behazardous. If you mustwalk with fins, whether inor out of the water,shuffle your feet and walkbackwards, looking overyour shoulder to seewhere you’re going.

A matter of balance.When donning fins out of the water,have your buddy steady you as youput on one fin at a time.

Check it out.Develop the habit of inspecting yourand your buddy’s equipment forcorrect positioning, adjustment andfunction before entering the water.

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can control the inflation. You’llnormally use the low pressureinflator because it’s quicker,easier and (surprisingly) savesair because it takes less effort.

Whether inflating orally orwith the low-pressure inflator,you’ll seldom find full inflationnecessary and may find ituncomfortable. Fill your BCDuntil you can float comfortably,which rarely takes more thanabout half its capacity.

To deflate the BCD, get into avertical — or relatively headup — position and depress theexhaust valve while holdingthe hose up. On some BCDs,you may use a “dump” valvefor convenient deflation with-out holding up the hose. Eitherway, you want to orient your-self so you put the spot where the hose joins the BCD (or the dump valve location) at the highest point.

Breathing UnderwaterOkay, this is it! You’re about to go under. But first (patience),listen to your instructor who may give you hand signals towatch for, and tell you what to do. Okay, now.

As you breathe from scuba for the first time, remember tobreathe slowly, deeply and continuously. Keep in mind the pri-mary rule in scuba — never hold your breath. While underwa-ter, watch your instructor for signals. Relax and enjoy theexperience. At first, you may not want to trust your scubaequipment, but after a few breaths, you realize — it works!You’ll love it.

Regulator ClearingOnce you’re comfortable with breathing underwater, your


More than one way.Although you usually gear up standing onland or in shallow water, that’s not alwaysthe case. There’s no reason why you can’tget into your equipment while seated ifyour physical characteristics require it.

Good ol’ lung power.To orally inflate the BCD, take abreath and blow two thirds intothe BCD hose, then release thevalve button. Your mouthdoesn’t have to be above waterwhile you blow.

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instructor will teach you how to take the second stage out ofyour mouth and replace it. Why? Because you need to dothis for some skills, to make a face at your buddy, or becauseit might get bumped out of your mouth, or you might drop itout by accident.

When the regulator leaves your mouth, it fills with water. Noproblem, though, because you can easily replace it, clear outthe water and resume breathing. There are two standardmethods: by exhaling into it (the exhalation method) and byusing the purge button (the purge method).

The exhalation method is as easy as it sounds. Simply blowinto the regulator with the second stage in an upright posi-tion (so the exhaust valve is the lowest point). The air forcesthe water out the exhaust valve. Remember that you mustexhale before inhaling, and that the regulator must be moreor less upright.

But what if you don’t have any air to clear with? Use thepurge method. Place the second stage in your mouth (again,more or less upright) and block the mouthpiece opening bysticking your tongue against it. This keeps water from

Chapter One 65

Push button buoyancy control.You’ll normally use the low pressureinflator because it’s quicker, easierand (surprisingly) saves air becauseit takes less effort. The inflator addsair to your BCD; the deflator buttonreleases it.

Going down.To deflate the BCD, get into a vertical —or relatively head up — position anddepress the exhaust valve while holdingthe hose up.

Remember the most important rule.You need to develop an important habitwhile you practice regulator clearing.When the regulator’s not in your mouthunderwater, always blow a small,continuous stream of bubbles bymaking an aaaahhh sound. This is soyou never hold your breath while scubadiving.

Inflator button

Deflatorbutton

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spraying into your mouth and making you cough.Now, push the purge button briefly. This releases airfrom the second stage, which forces the water out theexhaust valve. Now you can inhale.

Most of the time you’ll probably use the exhalationmethod because it’s the quickest and easiest, but youneed to know both methods. As you practice, turn theregulator mouthpiece downward when you remove itfrom your mouth. If you turn it upward, it may free-flow and waste air. If you forget, just turn the mouth-piece down and it will stop.

You also need to develop an important habit while you prac-tice regulator clearing. When the regulator’s not in yourmouth underwater, always blow a small, continuous stream ofbubbles. This is so you never hold your breath while scuba div-ing. As you’ve already learned, ascending with compressed airtrapped in your lungs can cause serious (possibly fatal) lung

over expansion injuries. By making a continuoussound, you keep the airway to your lungs open torelease expanding air.

Regulator RecoveryRecovering your second stage goes hand-in-hand withclearing it. Why? Because when you drop it from yourmouth, it tends to swing behind your back. Or, youmay need to find it after using your snorkel to swimto your descent point on the surface. Well, not toworry, you can find it by two methods: the arm-sweepmethod and the reach method.

To recover your regulator using the arm sweepmethod, come to an upright position and lower yourright shoulder. Next, extend your arm out and back,

along side your tank, then sweep it forward. The regulatorhose should end up against your elbow; grasp the hose whilesliding your hand down to the second stage. Put it back inyour mouth and clear it.

Sometimes the second stage snags on something, so yourecover it using the reach method. Reach back behind yourhead and find where the regulator hose attaches to the first


Sweep and recover.To recover your regulator usingthe arm sweep method, loweryour right shoulder, extend yourarm out and back along sideyour tank, then sweep itforward. The second stage hoseshould end up against yourelbow.

Reach and recover.To recover your secondstage using the reachmethod, reach behind yourhead and find where thehose attaches to the firststage. Follow it with yourhand until you locate thesecond stage.

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stage. Follow it with your hand until you locate thesecond stage. You may find it helpful to lift the bottomof your tank with your left hand, pushing it up and tothe right to make it easier for your right hand to reachthe first stage and find the hose.

You will practice regulator recovery during this con-fined water dive. Remember to blow bubbles and make a continuous sound when the regulator’s out of your mouth.

Mask ClearingBy the time you finish practicing regulator clearing

and recovery, you’ll notice that water tends to trickle into yourmask during a dive. No big deal, you just blow it back out.During this confined water training dive, you’ll learn to clearwater from a partially flooded mask.

You clear your mask differently without and with an optionalpurge valve. Without a purge valve, hold the top of the mask

firmly against your forehead, then look up slightlywhile exhaling through the nose. The air from yournose forces the water out the bottom of your mask.Note: Begin exhaling before tipping your head back toprevent water from getting in your nose.

With a purge valve, hold the mask snugly against yourentire face and look down, making the purge valve thelowest point in the mask. Exhale through your nose.The air forces the water out through the purge valve.

Mask clearing is easiest when you exhale steadily andcontinuously through your nose. Before you try it,

exhale an entire breath slowly and steadily through your nose.Since a mask has much less volume than your lungs, withpractice you may be able to clear your mask several times onjust one breath.

Swimming UnderwaterAfter you’ve practiced a few skills, you’ll be ready to swimaround a bit. The standard kick for diving is the flutter kick,but it’s different from the short, quick kick you use withoutfins. With fins, slow your kick and lengthen the stroke. Point

Chapter One 67

Things are looking up.To clear a mask without apurge valve, hold the top ofthe mask firmly against yourforehead, then look upslightly while exhalingthrough the nose.

Hold and exhale.To clear a mask with a purgevalve, hold the mask snuglyagainst your entire face andlook down, making the purgevalve the lowest point in themask, then exhale throughyour nose.

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your fins behind you, and move themprimarily from your hip, which getsthose powerful thigh muscles in gear.Your knees should bend only slightly.The down stroke applies the power,and the upstroke rests. When you kickproperly, you feel the tendons pull onthe top of your foot where it meets the ankle.

Fins only provide propul-sion when submerged, sokeep them underwaterwhen swimming at thesurface. Kick down farther and up less, while archingyour back upward to force your legs downward. Youmay find it easier to swim on your back or side for awider kick while keeping the fins submerged.

Don’t try to swim fast with scuba. Doubling your speedtakes four times the energy (it’s that exponential thingagain). Arm movements create drag and actuallyreduce momentum, so keep your arms still, trailing atyour sides. If you have a physical challenge thatrequires swimming with your arms and hands, thereare several effective techniques that may be useful.Ask your instructor for more information.

Equalization and Underwater SwimmingTo get used to equalizing and changing depth, you’llswim back and forth from shallow to deeper water.Relax, swim slowly to conserve air and energy.Equalize your ears as soon as you submerge and fre-quently (every metre/few feet) as you move to deeperwater. Don’t forget to equalize your mask by blowinginto it. It may take some practice before equalizationbecomes natural. Be patient, and don’t force it.

Swimming underwater you use long, slow flutter kicks.Stay with your buddy, and try to stay off the bottom.Your instructor will communicate with you using handsignals (you’ll discuss these before you go under); payattention to these and respond appropriately.


Flutter by.The standard kick for diving is the flutter kick.Point your fins behind you, and move themprimarily from your hip, which gets thosepowerful thigh muscles in gear. Your kneesshould bend only slightly.

Gettin’ around.Divers with a physical challenge that limitsleg mobility usually swim with their armsand hands. Note the special webbed fingergloves that increase hand swimming power.

Early and often.Equalize your ears as soon as yousubmerge and frequently (every metre/fewfeet) as you move to deeper water. Don’tforget to equalize your mask by blowinginto it.

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Managing Your AirWhile you’re underwater, get in the habit of checking your SPG fre-quently. Most SPGs have a marked caution zone — be sure to letyour instructor know if your air gets this low. Digital SPGs usuallyblink or otherwise alert your air is low. Your instructor will haveyou signal your air supply level, either indicating that you’re not

near the caution zone, or using your fingersto show how much air you have in bar/psi.

Alternate Air SourceIn the next two sections, you’ll start learn-ing about alternate air source types andhow to respond to an out-of-air emergency.You normally respond with alternate airsource use as the preferred means for shar-ing air with your buddy. During this con-fined water dive, you’ll learn the basics fordoing this.

As you’ll see, alternate air sources come inthree basic configurations. Regardless of type, though, you must beable to locate, secure and breathe from an alternate air source sup-plied by a buddy. The following procedures apply to the use of allthree types of alternate air sources; your instructor will demon-strate the specifics for the type you use during this dive.

The alternate air source sits in the chest area —readily accessible — and secured so that it pullsfree for use with a firm tug. Make a habit ofchecking where and how your buddy secures thealternate air source.

Depending on the alternate air source configura-tion, the donor (diver supplying air) may givethe receiver (diver getting air) the alternate, ormay give the receiver the primary air source(one in the mouth) and switch to the alternate.The important point is to agree on the procedurebefore the dive.

If you need your buddy’s alternate air source, first get your buddy’sattention and signal “out of air” and “share air.” Your buddy shouldrespond by swimming toward you, offering you a second stage

Chapter One 69

Know air to prevent no air.Get in the habit of checking your SPG frequently. It’sthe most effective way to avoid a low-on-air or out-of-air situation.

Stay out of the red.Most SPGs have a marked caution zone— be sure to let your instructor know ifyour air gets this low.

Caution zone

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mouthpiece. If not, you may need to locate and secure the alter-nate air source on your own and begin breathing.

Because there are many variations ofalternate air sources, use caution whenplacing the alternate regulator in yourmouth. If you put some types in upsidedown, you will have trouble clearing it andmay choke on some water. Once you havethe alternate air source, make contact withyour buddy. The best method for holdingon to each other depends on the alternateair source configuration, but generally youhold on to your buddy’s tank valve, arm,shoulder or BCD.

After you’re breathing comfortably, begin ascending. Keep eyecontact and hang on to your buddy while breathing normally.You and your buddy will adjust your own BCDs, with theascent rate controlled by the donor. (For this first time, you’llpractice stationary and swimming, but you probably won’tascend.)

Your instructor will demonstrate how to accomplish all thesepoints with the type of alternate air sources you and your

buddy have. This is a good skill to practiceor review frequently, especially when youdive with a new buddy or encounter anunfamiliar type alternate air source.

AscendingWhen your instructor gives the “up” signal,you and your buddy will swim togetherslowly to the surface. Reach up, look upand rotate (so you can see the entire area)

as you ascend. When you reach the surface, inflate your BCDenough to float comfortably. Keep your mask on and the regula-tor in your mouth until you swim back to shallow water.

Exiting the WaterYou’ll probably learn several methods for exiting the water dur-ing this course, each for a different diving situation. During


A friend in need.You normally respond with alternateair source use as the preferred meansfor sharing air with your buddy.During this confined water dive, you’lllearn the basics for doing this.

Look up, reach upand come up.As you ascend, reach up,look up and rotate so youcan see the entire area.When you reach thesurface, inflate your BCDenough to floatcomfortably.

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this dive, you’ll probably exit in shallow water. With yourbuddy’s help, slip out of your weight system and scuba unit inwater about waist deep. Take off your fins and place everythingon the pool’s edge, or hand it up to your buddy. Your instructorwill demonstrate the equipment removal procedure to use exit-ing the water.

Equipment Disassembly and CareWhen you finish, you need to disassemble your gear forrinsing and storage. First, turn off the tank air by turn-ing the valve clockwise gently until it stops. Next, pushthe purge button on the regulator to release all the pres-sure in it. If you forget to do this, the pressure will makeit almost impossible to take the regulator off.

Disconnect the low pressure inflator hose from the BCD,and unclip/release the SPG and alternate air source fromtheir holders. Remove the regulator by loosening the yokescrew, or unscrewing (DIN), being careful to keep waterfrom dripping into the high-pressure inlet on the firststage. Dry the regulator dust cap with a towel andreplace it.

Wrap and secure the BCD straps so they won’t drag and tan-gle. Release the tank band and slide off the BCD. Lie the tankdown so it can’t fall over while you rinse with fresh water andpack all of your equipment. This is even important after a pooldive because chlorine can harm your gear as much as saltwater can.

Chapter One 71

Shower so it lasts.It’s important to rinse all yourgear after a pool dive becausechlorine can harm it as much assalt water can.

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Knowledge Review—

Chapter One 73

1. True or False. An object is neutrally buoyant when it displaces an amount of waterless than its own weight.____________

2. Explain why buoyancy control, both on the surface and underwater, is one of the mostimportant skills you can master:

On the surface: ________________________________________________________________

Underwater: __________________________________________________________________

3. Fill in the blanks with the appropriate words: freshwater or saltwater.

“The same object would be more buoyant in ____________________ than it wouldbe in ______________________.”

4. True or False. Because water is denser than air, the pressure change for a given dis-tance ascent or descent is significantly greater in water than in air. ____________

5. Complete the following chart for a sealed flexible bag, full of air at the surface.

Depth Pressure Air Volume Air Density

0m/0ft 1 bar/ata 1 x 1

10m/33ft 1/2

30m/99ft 1/4

40m/132ft 5 bar/ata x 5

6. Circle the letter of the best definition for a squeeze.

a. A condition that causes pain and discomfort when the pressure outside an airspace of your body is less than the pressure inside an air space.

b. A condition that causes pain and discomfort when the pressure inside an airspace of your body is less than the pressure outside an air space.

7. Check each statement that describes a technique used to equalize air spaces during descent:

a. Block your nose and attempt to gently blow through it.b. Swallow and wiggle the jaw from side to side.c. Block your nose and attempt to gently blow through it while swallowing

and wiggling the jaw from side to side.

Chapter 1Knowledge Review—

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8. State how often you should equalize your air spaces during descent.

9. True or False. “If you feel discomfort in your ears while descending, continue down-ward until the discomfort is gone.” ______________

10. State the most important rule in scuba diving.

11. Circle the letter of the best definition for a reverse block.

a. A condition that occurs when expanding air cannot escape from a body airspace during ascent, causing pain and discomfort.

b. A condition that occurs when expanding air escapes from a body air spaceduring ascent, causing pain and discomfort.

12. Describe what action you should take if you feel discomfort during ascent due to airexpansion, whether in your ears, sinuses, stomach, intestines or teeth.

13. When scuba diving, why must your nose be enclosed in the mask?

14. Explain the best way to prevent water from entering your scuba tank.

15. Circle the appropriate answer. The most important feature for consideration whenpurchasing a regulator is:

a. The color b. The number of hoses it has c. Ease of breathing d. Size

Student Diver Statement: I’ve completed this Knowledge Review to the best of my ability,and any questions I answered incorrectly or incompletely I’ve had explained to me, and Iunderstand what I missed.

Name ________________________________________________ Date ________________________

Knowledge Reviews may not be reproduced in any form without the written permission of the publisher.

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PADI Open Water Diver Manual_01

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