A-07A Lightning Presentation

8/17/2019 A-07A Lightning Presentation

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Issued by the Anglo Technical DivisionThe information contained in this document is not prescriptive. It is indicative of good practice and is intended as information for site specific interpretation and application by theresponsible parties within the Anglo American plc Group. The material contained herein is based on information believed to be reliable, however, no representation or warranty,express or implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its subsidiaries or associated companies forany loss or damage of whatsoever nature arising out of the use of, adherence to or the lack thereof to any part of this information.

ATD, VOHE Tel: +27 11 638 3045

Administrative Contact: 5th Floor, 45 Main Street Fax: +27 11 638 2610 Marshalltown, Johannesburg e-mail: [email protected]

1 INTRODUCTION

Four persons have been fatally injured by lightning strikes during the past two years within the Group. Thepurpose of this bulletin is to provide guidance on protection against the risks of lightning. It covers:

a. An understanding of the risks of lightning, including how lightning develops, the characteristicsof lightning, warning signs of danger and victims of lightning strikes.

b. Lightning safety, including lightning safety policy, safety plan, decision tree, advance warning,notification, and evacuation.

c. Further guidelines on personal lightning safety, an overview of lightning detection equipmentand good lightning shelters are appended.

The intent is that operations may use the included to distil appropriate site specific Lightning Safety Plans.

December 2006 Bulletin No 147/2006


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CONTENT

1 INTRODUCTION................................................................................................................................ 1

2 UNDERSTANDING LIGHTNING ....................................................................................................... 3 2.1 How Lightning Works................................................................................................... 3 2.2

The Warning Signs...................................................................................................... 3

2.3 How Lightning Develops Between The Cloud And The Ground.................................. 3 2.4 Thunder ....................................................................................................................... 4 2.5 Negative Lightning And Positive Lightning .................................................................. 4 2.6 Facts About Lightning.................................................................................................. 4 2.7 Lightning Can Strike “Out of the Blue”......................................................................... 4 2.8 Lightning Strikes Anywhere......................................................................................... 5 2.9 A Near-Miss Can Be Deadly........................................................................................ 5 2.10 The Effects Of Lightning.............................................................................................. 6 2.10.1 Signs/Symptoms.......................................................................................................... 6 2.10.2 Care............................................................................................................................. 6

3 LIGHTNING SAFETY......................................................................................................................... 6 3.1 Policy and procedures................................................................................................. 6 3.2 Decision Tree .............................................................................................................. 7 3.3 Advance Warning of the Hazard.................................................................................. 7 3.3.1 The 30/30 rule ............................................................................................................. 7 3.3.2 Weather network information....................................................................................... 7 3.3.3 Lightning detectors ...................................................................................................... 8 3.4 Notification Of Affected Persons.................................................................................. 8 3.5 Evacuation To Safe Shelters....................................................................................... 8

4 REFERENCES................................................................................................................................... 9

Appendix 1: PERSONAL LIGHTNING SAFETY ..................................................................................... 10 Step 1: Planning...................................................................................................................... 10 Step 2: Establish the danger ................................................................................................... 10 Step 3: Inside the shelter......................................................................................................... 10 If Outdoors:.............................................................................................................................. 11 An imminent strike................................................................................................................... 11 Lightning strike victims: ........................................................................................................... 11

Appendix 2: AN OVERVIEW OF LIGHTNING DETECTION EQUIPMENT............................................. 12 1. Examples of some of the systems available on the market.............................................. 13 2. Features of lightning detectors. ........................................................................................ 14

Appendix 3: Good Lightning Shelters For Outdoor Workers ................................................................... 15 1. Summary..........................................................................................................................15 2. Behavior of lightning on struck objects............................................................................. 15 3. Safe and not safe structures ............................................................................................ 15 4. Shelters Unprotected from Lightning................................................................................ 15 5. Protected Shelters............................................................................................................ 16 6. Shelter placement on properties ...................................................................................... 16 7. Conclusion........................................................................................................................ 17

Examples of shelters for Lightning Protection ........................................................... 17


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2 UNDERSTANDING LIGHTNING

Lightning is a random, chaotic and dangerous fact of nature and it is an underratedweather hazard

2.1 How Lightning Works

Lightning is a form of electrical discharge between cloudsor between a cloud and the ground. The discharge maytake place between two parts of the same cloud, betweentwo clouds, or between a cloud and the ground. Lightningmay appear as a jagged streak, a flash in the sky, or in therarer form of a brilliant ball.

Lightning is caused by the attraction between positive andnegative charges in the atmosphere, resulting in thebuildup and discharge of electrical energy. During a storm,raindrops can acquire extra electrons, which arenegatively charged. These surplus electrons seek out a

positive charge from the ground. As they flow from theclouds, they knock other electrons free, creating a conductive path. This path follows a zigzag shapethat jumps between randomly distributed clumps of charged particles in the air. When the two chargesconnect, current surges through that jagged path, creating the lightning bolt.

Ice in a cloud seems to be a key element in the development of lightning. Storms that fail to producequantities of ice may also fail to produce lightning. In a storm, the ice particles vary in size from small icecrystals to larger hailstones, but in the rising and sinking motions within the storm there are a lot ofcollisions between the particles. This causes a separation of electrical charges. Positively charged icecrystals rise to the top of the thunderstorm, and negatively charged ice particles and hailstones drop tothe middle and lower parts of the storm. Enormous charge differences (electrical differential) develops.

2.2 The Warning Signs

High winds, rainfall, and a darkening cloud cover are the warningsigns for possible cloud-to-ground lightning strikes. While manylightning casualties happen at the beginning of an approachingstorm, more than 50 percent of lightning deaths occur after thethunderstorm has passed. The lightning threat diminishes afterthe last sound of thunder, but may persist for more than 30minutes. When thunderstorms are in the area, but not overhead,the lightning threat can exist when skies are clear.

2.3 How Lightning Develops Between The Cloud And

The Ground

A moving thunderstorm gathers another pool of positivelycharged particles along the ground that travel with the storm. Asthe differences in charges continue to increase, positivelycharged particles rise up taller objects such as trees, houses, andtelephone poles. Have you ever been under a storm and had yourhair stand up? Yes, the particles also can move up a person! Thisis one of nature's warning signs that say you are in the wrongplace, and you may be a lightning target!

The negatively charged area in the storm will send out a charge toward the ground called a steppedleader . It is invisible to the human eye, and moves in steps in less than a second toward the ground.When it gets close to the ground, it is attracted by all these positively charged objects, and a channeldevelops. The electrical transfer in this channel is seen as lightning. There may be several returnstrokes of electricity within the established channel that you will see as flickering lightning.

Stepped leader movesprogressively from cloud

to ground and can follow

one or s everal paths


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2.4 Thunder

The lightning channel heats rapidly and the explosiveexpansion of heated air causes sound waves heard asthunder. Since light travels faster than sound in theatmosphere, the sound will be heard after the lightning flash. Iflightning is seen and heard at the same time, that lightning is

close by!

2.5 Negative Lightning And Positive Lightning

Not all lightning forms in the negatively charged area low inthe thunderstorm cloud. Some lightning originates in the cirrusanvil at the top of the thunderstorm. This area carries a largepositive charge. Lightning from this area is called positivelightning. This type is particularly dangerous for severalreasons. It frequently strikes away from the rain core, eitherahead or behind the thunderstorm. It can strike far from the storm , in areas that most people do notconsider to be a lightning risk area. The other problem with positive lightning is it typically has a longer

duration, so fires are more easily ignited. Positive lightning usually carries a high peak electrical current,which increases the lightning risk to an individual.

2.6 Facts About Lightn ing

• One ground lightning strike can generate an electric charge of 100 million to 1 billion volts.

• Lightning can carry a current of between 25,000 to 250,000 amps (by comparison, a typicalhousehold outlet is 10 amps of current and the heart can be stopped by 0.01amps).

• The temperature of a typical lighning bolt is 30,000oC - hotter than the surface of the sun.

• Lightning strikes create powerful radio waves.

• Some 40% of lightning is forked with two or more ground attachment points.

• Most lightning strikes occur either at the beginning or end of a storm .

• Storms can grow from the small towering cumulus stage to a lightning producer in less than 30minutes.

• Storms commonly travels at a speed of 40 km/hr ormore.

2.7 Lightning Can Strike “ Out of the Blue”

Lightning can strike many kilometers from the parentthunderstorm, well outside the rain area and even beyondthe visible thundercloud. Lightning can also strike from

debris clouds several tens of minutes after the parentthunderstorm has decayed. Lightning strikes are arbitraryand random and it has been recorded traveling from cloudsources 60 km distant to cause injuries anddeaths. Lightning usually strikes at distancesbetween 4 and 10 km, but it commonly strikes atdistances of up to 15 km.

Thunder always accompanies lightning: “sound andlight.” Hearing thunder indicates that that lightning waswithin hearing range - 10 to 15km normally.

Thus, lightning safety requires a large standoff

distance from thunderstorms and a long standofftime after apparent thunderstorm decay.

If you can hear thunder, you are within st riking distance

6-10 km

15 km15 km

Anvi l Cloud


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2.8 Lightning Strikes Anywhere

Lightning does not "decide" where it will strike until thestepped leader descending from the cloud is about 30mfrom the ground or object that is struck. Thus, shortobjects in an open area can be struck by lightning evenif a tall object is nearby. If lightning strikes a nearby

object, shock can result either by direct contact or by aside flash.

2.9 A Near-Miss Can Be Deadly

There are five mechanisms of lightning related injury anddeath:

1. direct strike,

2. touch voltage,

3. side flash (or surface arc),

4. unconnected upward discharge, and5. step voltage.

About half of cloud-to-ground flashes form two or moreterminations when striking the earth. Lightning is knownto strike tall objects considerably below their tops. Manylightning discharges are likely to produce electrical arcsdeveloping radially along the ground surface from thestrike point. In the context of lightning safety, aconservative and prudent approach always is suggested.

If lightning strikes the ground, the high voltage gradientscause currents to flow in concentrated channels on thesurface or within the soil, and can injure people nearby.The associated step voltages and surface arcs,respectively, can be deadly more than 40m from thelightning strike point. In addition, there can be upwarddischarges tens of meters in length from tall objects(including people) that are located within tens of metersfrom the strike point.

Current can flow through the body if the legs areapart (step voltage)

.

STRIKE POINT30,000 Amps

50,000volts 3 0

m

0.5mStep Voltage

0 volts

Cows killed by step voltage


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2.10 The Effects Of Lightning

A lightning strike sends a strong electrical charge either through the body or over its surface. If ithits you or something close to you, lightening can cause serious injury. You may get burned ifyou have any metal on your body (a belt buckle, a zipper, or coins, for example). After a mildlightning injury, you will usually feel better within hours or days. A severe injury, however, cancause lasting damage to the brain, nerves, eyes, or ears, and may even be fatal.

2.10.1 Signs/SymptomsIn some cases, persons may be hit by lightening and not even know it. A mild strike may causepain, headache, confusion, tingling, numbness, or weakness, sometimes accompanied bydifficulties with vision, hearing, and memory. In a severe strike, the blast of electricity may tearthe clothing or shoes from your body. Burns may not be visible at first, but may appear hourslater. There may be broken bones, and if the heart is severely injured, it may stop.

2.10.2 Care

The victim does not carry any electrical charge. A severe lightning injury is an EMERGENCY.The victim may need CPR if the heartbeat or breathing has stopped. Hospitalisation is neededfor tests and treatment. Even if the injury is mild, a doctor should be consulted. Some of thesymptoms may only manifest some time after the incident such as increasing pain, blurred

vision, trouble hearing, worsening headaches, numbness or tingling in the arms or legs,increasing weakness and other symptoms.

3 LIGHTNING SAFETY

3.1 Policy and procedures

Thunder storms develop mostly on spring or summer days but can occur year round. There is a largevariation between regions in respect of the development of thunder storms and the frequency oflightning strikes and they are sometimes difficult to predict.

The threats of lightning should be risk assessed and formal lightning safety procedures that areappropriate for the region should be established.

Operations should prepare a Lightning Safety Plan and inform and train all personnel of its contents. Inprinciple, lightning safety is "anticipating a high-risk situation and moving to a low-risk location”.

All personnel who may potentially be exposed to the risks of lightning should be trained on lightningsafety and they should understand the company policy and safety procedures on the mitigation of risksassociated with inclement weather.

Essential components of any type of lightn ing safety system include:

1) A written lightning safety policy, together with a lightning safety plan;

2) Education about lightning and the organisation’s lightning safety plan;

3) Designation of a primary safety person (named designated weather watchers - persons who actively look for the signsof threatening weather and notifies the chain of command if severe weather becomes dangerous);

4) Have a means of monitoring local weather warnings and forecasts;5) Determination of when to suspend activities;6) Established a chain of command that identifies who is to make the call to remove individuals from the field;7) Designation of safe/not safe shelters for each venue;8) Notification to persons at risk;9) Planning for routing and evacuating people;10) Determination of when to resume activities;11) Carrying out of regular Lightning Action Plan drills;12) Reviewing and modifying the Lightning Action Plan as needed.

Al l indiv iduals have the r ight to leave a si te in order to seek shel ter if the person feels in dangerof impending lightning activity, without fear of repercussion or penalty.


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3.2 Decision Tree

."Lightning Safety Plans” should be site-specific, but they all share a common outline:

3.3 Advance Warning of the Hazard

3.3.1 The 30/30 ruleDuring thunderstorms, no place outside is safe, but the risk can be minimised by assessing thelightning threat and taking the appropriate actions. Attention should be given to early signs ofthunderstorms: high winds, dark clouds, rain, distant thunder or lightning. At this point, no new

task should be started that cannot be quickly stopped.

The 30second/30minute rule offers the best general lightning safety guidance where moresophisticated technology for identifying the danger is not available.

It takes the sound of a thunderclap about three seconds to travel one kilometer while the lightningflash is seen instantaneously. Therefore, for every three seconds between the flash of thelightning and the bang of thunder, lightning is one kilometer away. A thirty second Flash-to-Bangcount means lightning is 10 kilometers away.

If the “Flash-to-Bang” count is 30 seconds or less, the thunder storm is close enough (10 km) tobe dangerous – seek shelter.

However, the 30/30 rule is often difficult to apply since it may be difficult (confusing) to associate a

specific flash with the roar. The distance that thunder could be heard is about 10 to 15 km. If onecannot see the flash, or have difficulty to apply the 30/30 rule, just hearing the thunder is a goodbackup.

The following phrases are useful reminders:

When Lightning Roars, Go Indoors!

If you can see it (lightning), flee it

If you can hear it (thunder), clear it.

Wait for at least 30 minutes until the last thunder is heard before leaving the shelter.

Use an “all clear” signal that is different from the “warning” signal.

3.3.2 Weather network information

Forecasts by TV weather channels, radio broadcasts and other networks may be useful sourcesfor predicting potential developments in the local weather for advance planning of activities.

All persons should be encouraged to become “weather wise” and to consider the risks of lightningin the planning of their own activities. However, this should be the duty of the designated “weatherwatchers”.

Policy and Lightning Safety Plan

Advance Warning•Personal decision

•Weather forecasts

•Lightning detectors

Evacuation•Chain of command

•Notification

•Safe shelters

Resume Activities•Chain of command


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3.3.3 Lightning detectorsEspecially during the summertime, lightning activity can begin suddenly in areas of rain even if nolightning or thunder has yet occurred.

Lightning detectors can give advance notice to shut down dangerous operations or to suspendactivities before the arrival of thunder storms. They also may signal "all clear" conditions after thelightning threat has passed or if a storm might be passing at a safe distance.

Lightning detectors vary in complexity and cost, from large and expensive, dedicated equipmentpackages to relatively inexpensive hand held units and they could detect lightning from about 60kilometers to hundreds of kilometers. The technology applied (mostly the detection ofradio/electromagnetic waves emitted by lightning) and the intended use covers a wide range andthere are suitable systems available for a large variety of applications. Finding a detector and/orsignaling device that would suit site-specific requirements, easiest to use, and which offers themost cost effective solution is a matter of risk assessment and surfing the internet, enquiring fromthe market, etc.

However, beware of a false sense of confidence from detectors - none of them will detect all of thelightning all of the time. None of them will provide "first bolt out of the blue" information or forecastin advance the positions of lightning strikes on earth – they merely provide an unbiased indication

of the potential threat in line with the designed capabilities of the detector which generally exceedshuman perception.

An overview of lightning detection technology is given in Appendix 2.

3.4 Notification Of Affected Persons

Storms can grow from the small towering cumulus stage to a lightning producer in less than half anhour. A chain of command should be established that identifies who is to make the call to removeindividuals from the field.

Designated weather watchers should be named - persons who actively looks for the signs of threateningweather and notifies the chain of command if severe weather becomes dangerous.

If it will take a while to reach shelter (more than a few minutes) other arrangements should be made to

reach the safe place before lightning is an immediate threat.

In other instances, e.g. where potentially dangerous operations such as working with explosives isinvolved, there may be duty-to-warn issues – in these circumstances the use of lightning detectionsystems may be essential.

3.5 Evacuation To Safe Shelters

Having established the hazard, the other defenses for mitigating the hazard should be considered:

• Where is a safe refuge?

• How long will it take to get there?

• How long should persons stay there?

While nothing offers absolute safety from lightning, some actions can greatly reduce the risks. If a stormis approaching, avoid being in, or near, high places, open fields, isolated trees, unprotected gazebos,rain shelters, communications towers, flagpoles, light poles, metal fences, convertibles (back of a LDVcovered with canvas), and water.

A designated safe shelter for each venue should be identified during the planning stage and by use ofappropriate signage.

Some places are safer than others. Large enclosed structures are safer than smaller, or open,structures. Avoiding lightning injury inside a building depends on whether the structure incorporateslightning protection and its size. When inside during a thunderstorm, avoid using the telephone, taking ashower, washing hands, doing dishes, or having contact with conductive surfaces, including metaldoors, window frames, wiring and plumbing. Generally, enclosed metal vehicles, with the windows rolled

up, provide good shelter from lightning. An overview of safe and less safe shelters is given in Appendix 3.

More than 50 percent of l ightning deaths occur after the storm has passed. This is because most peopledo not realise that the lightning threat may persist for more than 30 minutes after the storm has moved on.


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4 REFERENCES

Following are some usefull internet sites regarding lightning safety:

http://www.lightningsafety.com/

http://www.stormwise.com/http://www.viasala.com/http://www.weathershop.com/boltek/


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APPENDIX 1: PERSONAL LIGHTNING SAFETY

The vast majority of lightning casualties can be easily, quickly, and cheaply avoided if the proper rulesare followed. People need to increase their awareness of lightning hazards, their knowledge of lightningsafety and the Company Safety Plan.

Step 1: Planning

Plan around the weather to avoid lightning hazards. Pay attention to the daily forecasts so thatone knows what to expect during the day. Also pay attention to early signs of thunderstorms. Atthis point, do not start any new task that cannot be quickly stopped.

Lightning Warning SignsIn addition to the obvious warning of an ominously darkening sky, there are certain conditions thatcan alert persons to a lightning danger before the strikes threaten. You are in a 'danger zone' andneed to seek immediate shelter if you experience any of the following:

• Raindrops or hail: Rain of any intensity (but more so with heavy rain) may signal the presenceof a thunderstorm cloud directly overhead, even if it has not yet produced any lightning orthunder . Large, 'fat' raindrops are ominous, telltale signs of a towering cloud that has thepotential to produce a lightning strike at any second.

• Audible thunder or visible flashes: If you can see lightning or hear thunder at all, you arewithin range of the next strike.

• Large, towering clouds: Cumulonimbus (thunder) clouds can develop rapidly overhead, evenamong pleasant-looking skies; sometimes leaving no 'dark sky' appearance that oftenotherwise precedes a thunderstorm. A growing cumulonimbus cloud's upper edges will usuallylook hard and rounded, like cauliflower, as it protrudes skyward.

• Static on an AM radio: Distinctive crackling and popping sounds on an AM radio indicate thatlightning is occurring in your area.

• Lightning Detector Alarms: Several handheld lightning detectors are on the market thatsounds an alarm when lightning occurs within a set distance. These battery-operated detectorsare commonly used by personnel at golf courses, pools, parks and beaches. If your job or past

time involves large amounts of time outdoors, a portable lightning detector could be a goodinvestment.

Step 2: Establish the danger

Count the number of seconds from when the lightning flash is seen until the thunder is heard. Ifthat count is 30 seconds or less, you are in immediate danger. Stop what you’re doing and seeksafety in a substantial building and alert others in line with the Safety Plan.

Do not wait for the rain. Many people take shelter from the rain, but most people struck bylightning were not in the rain. Where practicable go quickly inside a completely enclosed building,not a carport, open garage or covered patio. If no enclosed building is convenient, get inside ahard-topped all-metal vehicle. A vehicle with a solid metal roof and metal sides is a reasonablesecond choice. Convertibles, cars with fiberglass or plastic shells, and open framed vehicles donot count as lightning shelters.

MYTH: Cars are safe because the rubber tyres insulate them from the ground.

TRUTH: Cars are safe because of their metal shell.

Step 3: Inside the shelter

Inside the building, stay off corded phones, computers and other electrical equipment that put youin direct contact with electricity or plumbing. Buy ground fault protectors for key equipment. Insidea car, as with a building, avoid contact with conducting paths going outside, e.g. close thewindows, lean away from the door, put your hands on your lap, do not touch the steering wheel,ignition, gear shifter, or radio.

Clouds don't have to be directly overhead for lightning to strike; it can arc out from thethunderstorm for a distance of up to 15 km. Even when the sky looks blue and clear, be cautious.If you hear thunder, remain in a safe shelter. Therefore, extreme caution should be practiced evenafter a thunderstorm has passed.


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If Outdoors:

A l ightning strike can seriously al ter your li fe as you know i t. In other words, go with yourbest bet: Play it safe and do not be caught outdoors when lightn ing is around.

If caught outdoors, the focus on protecting yourself from lightning should not be on what type ofobjects you are wearing, standing by, or carrying, but rather on avoiding the locations where

lightning can strike - which, essentially, is anywhere outdoors or in unprotected structures.You are in equal danger of a lightning injury outdoors regardless of whether or not you arestanding near, carrying, or wearing any metal objects. Lightning is a force that is not influenced bysmall objects on the ground, so distancing yourself from small metal objects will not makeyou safe from lightning.- it remain a matter of chance whether lightning will strike near you ornot. Metal objects like umbrellas, golf clubs, bicycles and fences will attract a lightning channelonly if the strike is already a few feet away - in which case you would still experience an injuryfrom being that close to begin with.

It is commonly understood, for instance, that one should stay away from trees if outside during astorm. There is some merit to that statement, but the truth is that there is still in danger fromlightning if you are outdoors at all. If you are caught outside, stay away from tall, isolated objectslike solitary trees, flagpoles, or posts. Remember that, contrary to the myth, lightning does notalways strike the tallest or largest object - it can strike anywhere. Also stay away from shorelines,railroad tracks, and metal fences which could bring current from a 'far-away' lightning strike to you. Although still not as safe as being indoors, dense woods provide a little protection due to the largenumber of trees that decrease the chances of lightning strike to a tree next to you. However inthis, and any other case, do not stand close to any of the trees.

Jewelry, spiked shoes, watches or hair berets will do nothing to influence a lightning strike'sground termination. However, if you are hit directly, lightning will usually flow through any metalobjects on your person, superheating (even vaporising) them and causing burns.

An imminent s tr ike A close or direct lightning strike will sometimes give you a short warning a few seconds before the

event, usually in the form of:• A soft or loud buzzing, clicking, hissing or cracking sound.

• A tingling sensation

• Hairs on the arm or head standing on end

• Nearby metal objects emitting a soft, blue-white glow called ‘St Elmo’s Fire’.

These signs indicate a direct strike may occur within seconds. In most cases, you will not havetime to react. However, if you are unable to reach shelter and you experience any of these signs,or if you otherwise feel that you are in immediate danger, assume the following position quickly:

Move your feet close together, crouch down, and grab your ankles. Tuck your head down as far asyou can. Do not lie flat on the ground. If there is a group of people they should spread out and not

bundle together.

Remember, this is a desperate last resort; you are much safer if you follow the previous steps andavoided this high-risk situation. Crouching merely reduces the risk of step voltage and arcs.

Lightning strike victims:

Victims of lightning strikes are not always initially in a fatal situation. Typically a lightning strike willcause cardiac and/or respiratory arrest that can be corrected by proper resuscitation (CPR). Manylightning-related deaths occur when the victim does not receive the proper medical attention. Ifyou witness a lightning strike incident;1. Survey the scene for safety.2. Activate the local Emergency Response System.

3. Note that lightning victims do not “carry a charge” and are safe to touch.4. If necessary, move the victim with care to a safer location.5. Evaluate airway, breathing, and circulation, and begin CPR if necessary.6. Evaluate and treat for hypothermia, shock, fractures, and/or burns.


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APPENDIX 2: AN OVERVIEW OF LIGHTNING DETECTION EQUIPMENT

Lightning hazards can be mitigated by advanced planning. One part of the lightning safety programshould include an early detection and warning alarm package. Lightning detectors vary in complexityand cost from expensive, large dedicated equipment packages to relatively inexpensive handheldmodels.

Available technologies of the present day lightning detectors include:

1. Radio Frequency (RF) Detectors. These measure energy discharges from lightning. They candetermine the approximate distance and direction of the threat.

2. Inferometers. These are multi-station devices, much more costly than RF detectors and theymeasure lightning strike data more precisely. Usually they require a skilled operator.

3. Network Systems. National lightning detection networks are available in some countries wherelightning strikes are reported to a central station. Local storm data is available and past strikeinformation could be used for risk assessment purposes.

4. Electric Field Mills. These pre-lightning equipments measure the potential gradient (voltage)changes of the earth's electric field and report changes as thresholds build to lightningbreakdown values.

5. Optical Monitors. These can provide earlier warning as they also detect cloud-to-cloud lightningthat typically precedes cloud-to-ground lightning.

6. Hybrid Designs. These monitors use a combination of the other single-technology designs. Twoor more sources of information (for example, cloud-to- cloud, cloud-to-ground, opticalrecognition, EFMs) may be better than just one.

Lightning Detection Options – Accuracy vs Cost vs Complexity

Source of Information Accuracy Cost Complexity Level Hearing thunder Danger is near None Simple

TV weather channel General information None Simple

Small handheld General information From $70 Simple

Handheld detectors 50-60% accurate $200 to $700 Simple to Somewhat

Boltek portable system 70-80% accurate Up to $1,500 Somewhat

WXLine base unit system 90-95% accurate Up to $7,000 Somewhat

Beware of a false sense of confidence from detectors; none of them will detect all of the lightning all ofthe time. None of them will provide "first strike/bolt out of the blue" information or forecast in advancethe positions of lightning strikes on earth.

The Radio Frequency (electromagnetic) detectors are used most widely. These detector receiveralgorithms operate at different frequencies and wavelengths. The operating range of the differentmodels could fall within an overall range between 10kHz and 120 MHz, depending on the application.

Detectors can display early warning of lightning conditions to hazardous operations. Some detectorscan start/stop standby power generators. A signaling or alarm notification method is essential to alertfield personnel of developing dangerous circumstances. Two-way radios, remote activation sirenpackages, strobe lights, and other methods are available.

Finding a detector and/or signaling device that would suit site-specific requirements, easiest to use, andwhich offers the most cost effective solution is a matter of risk assessment and surfing the internet,enquiring from the market, etc.


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1. Examples of some of the systems available on the market.

Hand held StrikeAlert $70 Hand held ScyScan $ 250

Hand held Bol teck Thunderbol t $650 Fixed installation Lightning Alert $200

Portable Boltek LD 250 system with mapping

software $1,000+

Fixed installation Wxline hybrid system with

software $7,000+

Example of Boltek software


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2. Features of lightning detectors.

When selecting lightning detection systems, the application and reliability (of detecting lightning,durability, batteries, usability) are the most important considerations.

Other features of lightning detectors that could be considered, depending on site specific needs,

include:

• TEXT SCREEN DISPLAY vs LED

• USER SELECTABLE MENU OPTIONS

• LIGHTNING DETECTION RANGE INDICATOR

• THUNDERSTORM CELL TRACKING

• STORM IS LOCAL DISPLAY

• TIME TO CLEAR DISPLAY

• USER SELECTABLE BACKGROUND NOISE ROUTINES

• USER SELECTABLE ALARM DISTANCE

•

SEVERE STORM WARNING• SECOND ALARM RANGE OPTION

• SQUALL LINE WARNING

• HIGH/NORMAL STORM DETECTION SENSITIVITY

• MULTIPLE STORM CELL WARNING

• IDENTIFY CLOSEST STORM CELL

• WARNING MODES

• STORM DISTANCE DISPLAY

• EXTERNAL SPEAKER JACK

• STORM APPROACHING DISPLAY

• STORM APPROACH SPEED DISPLAY• ESTIMATED TIME OF ARRIVAL DISPLAY

• POWER SUPPLY OPTIONS

• WATER RESISTANT

• SOFTWARE AND UPGRADES

• LOCAL SUPPLIER AND TECHNICAL SUPPORT


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APPENDIX 3: GOOD LIGHTNING SHELTERS FOR OUTDOOR WORKERS

1. Summary

Sudden thunderstorms may bring urgency for outdoor workers to cease work and quickly relocate torefuge. Ordinary wood buildings provided for worker comfort, lunch breaks or safety from rain or sun are

not safe from lightning. “Safe” and “not safe” structures and their placement on typical properties arediscussed, together with some examples of suitable shelters.

2. Behavior of lightning on struck objects

High-frequency current flowing on a metal conductor generates an electromagnetic field. One effect ofthis is to confine electrical flow towards the outside of it. This is called “skin effect.” The thickness of thelayer of restricted penetration is called “skin depth.” Skin depth is proportional to the square root of theinverse of the frequency. The higher the lightning frequency, the smaller the depth.

People react much differently to lightning than do metal objects. The human body, being some 65% saltand water, is a good conductor. Direct lightning strikes can follow either through internal or externalpathways or both. Indirect lightning damage mechanisms include:

1) flashover from an intended conductor (for example, a gazebo or tree) to an unintended conductor(such as a person seeking refuge from rain or hail);

2) step and touch voltages where a person’s hands or feet intercept electrical differentials, which thenseek to equalise via the body; and

3) interrupting the normal electrical heart beats leading to arrhythmia.

3. Safe and not safe structures

Small open shelters are common on athletic fields, golf courses, parks, roadside picnic areas,

schoolyards, and elsewhere. Many of these shelters are built to protect against rain or sun, not lightning.What can be done to minimise risk/maximise safety for people inside them under direct and indirectlightning strike conditions? Although there is no such thing as a lightning-proof small outdoor shelter, aproperly designed and installed lightning protection system may make a difference. Sometimes thedifference is between life and death.

A basic lightning protection system (LPS) against direct strikes to an ordinary structure includes:

1) air terminals,

2) down conductors, and

3) ground terminals.

These three elements of the LPS must form a continuous conductive path (actually at least two paths)for lightning current, with all connections between the elements typically being accomplished by boltingor welding. The function of the LPS is to intercept lightning and safely direct its current to ground and tointercept electric arcs developing along or under the ground surface toward the shelter from lightningstrikes.

Various standards on LPS are available for reference, e.g. the European Standard BS EN 62305, theInstitute of Electrical Electronics Engineers IEEE std 80, etc.

4. Shelters Unprotected from Lightning

In the absence of the three-element lightning protection system described above, the structure shouldbe considered unprotected from lightning. Small shelters with or without lightning protection should beavoided where possible during thunderstorms.


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5. Protected Shelters

A small shelter equipped with a properly designed and installed LPS may provide reasonable protectionfrom direct lightning. It is essential, however, that a person inside the shelter does not touch anyelement of the LPS and tries to position himself or herself at approximately the same distance from alldown conductors. Electrical signs, pop machines, water faucets, irrigation controllers, etc. can increasepersonal hazards inside the shelter should lightning strike nearby. A small shelter, even one protected

as described here, should be viewed as the last resort option. Refuges with much higher safety levelssuch as large buildings and fully enclosed metal vehicles should be sought instead when time permits.

A small recreation shelter with peaked roof should have an overhead shield wire system or Franklin rodsystem. Again, there are reference standards available for the installation of adequate LPS for thesetype of structures.

Knowing the above described behaviour of lightning upon, say, an automobile, it is apparent that a fullyenclosed metal vehicle is also a safe shelter. Other all-metal mobile equipment such as airplanes,buses, vans, and construction equipment with enclosed mostly-metal cabs are also safe. These areexamples of an everyday “Faraday Cage” where the charge and current is confined to the outside metallayers.

It should be emphasised, however, that the “outer metal shield” should not be compromised. Thismeans that:

1) Windows need to be rolled up.

2) Person must not make any interior contact with external objects, such as radio dials, metal doorhandles, two-way radio microphones, etc.

3) Person should avoid all other objects that penetrate from inside to outside.

Unsafe vehicles include those made of fiberglass and other plastics, plus small riding machinery orvehicles without enclosed canopies, such as motorcycles, farm tractors without fully enclose cabin, golfcars, and the load trays of LDVs that are open or covered with canvas or with a fiberglass canopy.

Metal buildings are safe places. So, too, are large permanent structures made of masonry and of wood. Again, the caveat is not to become a part of the pathway conducting lightning. This means avoiding allelectrical circuits, switches, powered equipment, metal doors and windows, hand rails, and so on. Smallpost-supported structures, such as bus stops or picnic shelters, are not safe and cannot be made safefor people.

Metal shipping containers, for example, can be easily modified to become cheap, effective, portable,and rapidly deployable shelters – note other safety and health requirements are also applicable.

6. Shelter placement on properties

Each site location is unique and different and shelters should be located where the probability oflightning strikes might be lower. That is, in relatively low areas, preferably surrounded by a large number

of trees of approximately the same height. They should not be located on hilltops, near metallic fences,power poles, tall trees, or near water.

However, they should also be within reach from the working areas. It is generally proposed that 3 to 4minutes, even under rapid evacuation, should be adequate for reaching safety if supported byappropriate warning systems.

Following are some examples of decisions to be made when seeking shelter:

1) Is there a pickup truck nearby that one can get to faster than an alternative shelter?

2) If there is a choice between a metal shelter and a plastic/wooden shelter at equivalent distances,choose the metal shelter.

3) If the only nearby structure is locked, seek an overhanging roof, where possible.

4) If one is caught with no shelter of any type nearby, crouch to the lowest possible position, avoiding allnearby metal objects.

An incident report should be filed in the event of 3 and 4 above if it occurred during real or simulated conditions


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7. Conclusion

To attain 100% lightning safety is not possible. But pre-planned defenses can assure a best attempt toachieve high levels of safety. Hear thunder? When to stop activities? Hear more thunder? Get ready toevacuate to safe shelter. What is a safe place? How long to stay inside the shelter? These and other

questions must be answered well in advance of the thunderstorm evacuation emergency.

Examples of shelters for Lightning Protection

(source: http://www.lightningsafety.com/nlsi_pls/outdoor_worker_shelters.html)

Good Poor

•Metal roof (air terminal)

•Wooden structure (no down conductor)

•Poor earthing

•Conducting rails



•Poor earthing

•Canvas provide no protection

•Cab of LDV provide better protection



•Poor earthing


•Open sides –no protection

Features of poo r shelters

A-07A Lightning Presentation

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Transcript of A-07A Lightning Presentation