Fix Installation (CO2)

7/28/2019 Fix Installation (CO2)

1/10

183

FT 31FIRE FIXED INSTALLATION SYSTEM

CO2

OBJECTIVE

1. To explain the function, operation and maintenance of CO2 fire fixed installationsystem.

REFERENCE

2. Manual of Fireman ship Book 9.

CONTENTS

3. Introduction. In our study of fire extinguishment, we noted that carbon dioxide is

one of them. However we only searched the surface. We must now go bit deeper. Withinthe next few lectures we will study the following pertaining to CO 2 system installation.

a. Properties of carbon dioxide.b. Extinguishing properties.c. Limitations as an extinguishing agent.d. Methods of application.e. CO2 system and components.f. Operation of systems.

4. Properties of Carbon Dioxide:

a. General Properties:

(1) Non-combustible.(2) Non-reacting with most substances.(3) Provides its own pressure for discharge from container.(4) Since it is a gas, it spreads to all parts of the fire are.(5) Electrically non-conductive.(6) Leaves no residue.

b. Thermodynamic Properties:

(1) Under normal conditions it is a gas.

(2) Liquefied by compressing and cooling.

(3) Carbon dioxide in a closed container may exist as a liquid or gas at 75psi and 69.9F and the critical temperature of (87.8F) Triple Point.

(4) At 87.8F density of vapor is equal to the density of the liquid and theclear demarcation of the two phases disappears.

(5) Below - 69.9F (at 75 psi) carbon dioxide may be present in vapor,liquid and solid forms.

(6) When liquid carbon dioxide is discharged to atmospheric pressure, aportion instantly flashes to vapor, the remainder is cooled by evaporation andis converted to finely divided snow (dry ice) at a temperature near - 110F.

(7) The portion that is converted to dry ice depends on the temperature of

the stored liquid 46% of the liquid at 0F, 25% for liquid at 70F.


2/10

184

c. Storage:

(1) Liquid carbon dioxide is stored in high pressure cylinders at normalambient temperature or in low pressure refrigerated containers near 0F.

d. Discharge Properties:

(1) Discharged liquid CO2 has a white cloudy appearance due to finely

divided dry ice particles together with vapor.(2) Some water vapor from atmosphere also condenses due to lowtemperature (1 - 110F) and this creates additional fog.

(3) Cooling effect of dry ice continues for some time and helps to reducethe temperature after a fire.

(4) Then continuing cooling effect is damaging to extremely temperaturesensitive equipment and therefore direct discharge into or at and heavy-discharge at must be avoided with temperature sensitive equipment.

e. Density:

(1) CO2 is time as heavy as air.

(2) CO2 which is just discharged since is very cold has a greater density.This is why it able to surround the air above the burning surfaces andsmother.

(3) Any mixture of CO2 and air is heavier than air at the sametemperature, so air containing more CO2 will settle to the lowest level.

f. Toxicity:

(1) CO2 is mildly toxic but produces unconsciousness and death bysuffocation when present in fire extinguishing concentration.

(2) Most persons can with stand up to 9% of CO2 for a few minutes

without losing consciously.

5. Extinguishing Properties. Carbon dioxide effective as a extinguishing agent mainly

because it reduces the oxygen constant of the atmosphere to a point where the air aroundthe fire is unable to support the fire. The cooling effect of discharged to the burning materiel.

a. Extinguishment by Smothering

(1) In any fire heat is given off by rapid oxidation, some of this heat bringsthe unborn fuel to its ignition temperature but a large part of the heat is lost byradiation and convection, especially in the case of surface burning materiel. Ifnow CO2 is discharged into this atmosphere, the oxygen content in the air isreduced , so less oxygen content in the air is reduced, so less oxygen is

available to bring the unborn fuel to its ignition temperature and eventually thefire dies out.

(2) The minimum concentration of CO2 needed to extinguish surfaceburning material e.g. liquid fuels is easily calculated as heat loss due toradiation and convention is reasonably constant, but it is difficult to calculatethe needed concentration for solid materiel because of the physicalarrangement of the solid materiel and the shielding effect due to it.

b. Extinguishing by Cooling. The cooling effect of discharged CO2 is mosteffective only on surface fires. The CO2 has to be discharged directly and in largequantities on to the burning surface.


3/10

185

6. Limitation as an Extinguishing Agent:

(2) CO2 may be used to fight the following classes of fire:

(1) Class A.

(2) Class B.

(3) Class C Note risk of explosion after extinction must be carefullyconsidered.

(4) Fire involving life electrical apparatus.

b. Use of CO2 on Class A fires is limited mostly by:

(1) Low cooling capacity (particles of dry ice do not Wet of penetrate).

(2) Inadequate enclosures for retaining and extinguishing atmosphere.

c. Hot Surfaces and Embers:

(1) Liquid fuel fires are extinguished by discharging directly on burningmateriel.

(2) No enclosure is needed.

(3) 30 sec. discharge adequate to cool below resignation temp.

(4) Longer discharge time is needed to cool severely over heated surfaceor metals and glowing embers from carbonaceous materiel.

d. Oxygen-containing Materiel and Reactive Materiel:

(1) When oxygen containing materiel are on fire CO2 in ineffective as thefire dose not depend on a atmospheric oxygen for combustion (cellulosenitrate).

CO2 Fire Curtain

Heat DetectorDischarge Nozzle

Smoke Detector

Signal Light

24V Siren

Control

Panel

Key Switch

CO2 Cylinder

Pressure Switch

Fig. 1 : Installation of CO2 System


4/10

186

(2) Fire involving reactive metals (such as sodium), potassium,magnesium, titanium and zirconium and fires involving metal hydrides cannotbe put out by CO2. The metals and hydrides decompose CO2.

e. Hazards to Personnel:

(1) CO2snow in discharge cute down visibility.

(2) Noise of discharge frightens inexperienced and unexpecting people.(3) Oxygen-deficient atmosphere is produced in enclosed space or room.If large volumes of CO2 is discharged and drift, this may settle in adjacent lowspaces such as tunnels and pits.

7. Methods of Application:

a. Total Flooding. The discharge of enough agent into an enclosure or room tocreate an extinguishing atmosphere throughout the enclosed volume.

(1) CO2 is discharged through nozzles designed and located to develop auniform concentration of CO2 in all parts of the enclosure.

(2) Quantity of CO2 required achieving and extinguishing atmosphere iseasily calculated based on:

(a) Volume of room.

(b) Concentration required for he combustible materiel in the room(Acetylene 55%; Gasoline 28%).

(3) The integrity of the enclosure is itself important. When total flooding iscarried out. There should be no openings around the sides and at the bottomthrough which the gas can escape.

(4) When openings must be present or cannot be closed then additionalCO2 to compensate for loss through which the gas can escape.

(5) Minimum concentration used in CO2 total flooding system is:

(a) 34% by volume for surface burning materiel such as someliquid fuels.

(b) 50% for electrical wirings and small electrical machines.

(c) 60% bulk paper.

(d) 75% for storage.

b. Point Protection of Local Application:

(1) Discharged directly onto burning surface by especially designed

nozzles.(2) Should cover all combustible areas to which fuel may spread.

(3) Should be designed to extinguish as quickly as possible.

(4) Discharge should be for at least 30 sec or longer if required to cool offany potential source of resignation.

(5) Nozzles designed for low velocity to avoid splashing and airentrainment.

(6) Automatic detection necessary for fast response to minimize heatbuilds up in fire area.

(7) Enclosure not essential but helps to retain CO2 in fire area.(8) Local application can be used together with total flooding to providefast extinguishment.


5/10

187

c. Extended Discharge:

(1) Used when enclosure is not leak proof to retain extinguishingconcentration to the required time.

(2) Normally a reduced discharge rate following a high initial rate.

(3) Extended discharge rate is based on leakage rate.

(4) In local application systems it is used to provide prolonged cooling tosmall hot spots.

d. Hand-Hose Lines:

(1) Consists of hand hose connected to fixed supply of CO2.(2) Can be used for total flooding or point protection.(3) CO2 storage should at least allow 1 min discharge.(4) Minimum burst present of hose lines shall be:

(a) 5,000 psi if connected to high pressure supply.(b) 1,800 psi if connected to low pressure supply.

(5) Hoses are equipped with quick opening shut off nozzle.(6) Hoses are not under pressure until the actuating valves are opened.

e. Determining System Types. Careful planning must be done when decidingto install CO2 fire extinguishing systems. The principal hazard may be one that willproduce a surface fire, but within the fire area, there may be other materials that canproduce a deep-seated fire. It is therefore important that following questions areasked and clearly answered before deciding on a CO2 extinguishing system.

(1) Considering the speed of fire detection and fire extinguishment of thecontemplated system, will there be enough for a deep-seated fire to develop?

(2) If deep-seated fire does develop, will circumstances be such that therewill not be resignations with additional loss.

(3) If additional losses are a possibility, can they be reduced by any otherback-up system be designed to extinguish it, because of high valves involvedor operation requirement.

(4) If deep-seated fire is expected, must a system be designed toextinguish it, because of high valves involved or operation requirement?

8. Carbon Dioxide System Components. The ability of a carbon dioxide system toput out a fire depends upon:

a. The way in which it is discharged into the fire area.b. Rate of application.

c. Total quantity discharged.

9. Designed Features That Affect These Variables are:

a. Method and location of CO2 storage.

b. Piping.

c. Fittings.

d. Nozzles.

(1) Carbon Dioxide Storage. Carbon dioxide supply may be stored inhigh pressure of low pressure containers. The differences of the pressuremaintained in these two types of containers, influences the design of thesystem.


6/10

188

(2) High Pressure Systems:

(a) Containers are usually cylinders.

(b) CO2 stored at atmospheric temperature.

(c) Important that containers are designed to withstand themaximum expected temperature.

(d) Temp 70F: pressure in container 840 psig.

(e) Rapid pressure increase when temperature is raised.

(f) 130F chosen as maximum possible temp for storagecontainers.

(g) This maximum (130 F) provides a margin of safety below the3,000 psi bursting pressure of the frangible disk in container.

(h) Storage cylinders are designed, tested and filled to nationalstandards.

(i) Max permitted filling density is equal to 68% of the weight of

water that the container can hold at 60%.(j) In terms of CO2 filling density is 42.5 lb per cu ft cylindervolume.

(k) Fire extinguishing cylinders are fitted with an internal diptube/so that liquid is discharged from the bottom, when the cylinder isupright and the valve open.

(3) Low Pressure System:

(a) Containers are pressure vessel with a design working pressureof 325 psi.

(b) They are maintained at a temperature of approximately OF,by insulation and refrigeration, at this temperature the pressure isapproximately 300 psi.

(c) A compressor controlled by a pressure switch in the tankcirculates refrigerant through coils near the top of the tank.

(d) Economical to store CO2 from 500 lb several hundred tons.

(e) Liquid CO2 is delivered through pipelines from low pressurestorage units to open nozzles in capacities as high as 2,500 lb permin.

(f) Filling density not important as with high pressure containers.

(g) Low pressure container will not become liquid full for thefollowing reasons:

- Temperature is controlled by refrigeration.

- Use of pressure relief valves to cause evaporation andresultant liquid cooling.

(h) It is only necessary to provide sufficient vapor space to providefor expansion of the liquid under maximum storage temperature thatcan be obtained with the pressure relief valve.

(i) Filling density ranges from 90 to 95%.

(j) Relief valves prevent pressure from exceeding safe limits, ifthe refrigeration fails.


7/10

189

(k) Relief valves prevent pressure from exceeding safe limits, ifthe refrigeration fails.

(l) Relief valves include a diaphragm valve set to bleed or vaporwhen the pressure exceeds 341 psi; and a relief valve set to operateat 357 psi for more rapid release.

(4) Piping and Fittings:

(a) Normally empty.

(b) Used to take CO2 from the storage container to the opennozzle at the fire are.

(c) Liquid CO2 enters the piping through the dip tub.

(d) Friction lowers pressure.

(e) Liquid CO2 boils as pressure decreases and results in amixture of liquid and vapor in piping.

(f) Vapor increases in volume as mixture passes through pipingwith a continuing drop in pressure.

(g) Rate of pressure drop not linear, but increases a t low pressuredue to:

i. Changing volume.ii. Increasing velocity.

(h) Equations are used to calculate two phase flow and pressuredrop size of pipes to provide the desired flow rate. Important in localapplication where rate of discharge at each nozzle is critical.

(i) Flow calculations are based on an average storage pressure of750 psi during discharge for high pressure and 300 psi low pressures.

(j) Minimum nozzle pressure is 300 psi for high pressure and 150psi.

(k) Minimum nozzle pressure have been set to avoid dropping to75 psi, where liquid CO2 would be converted to dry ice (triple point)and block the discharge points.

(l) Minimum burst pressures of pipes and fittings are 5,000 psi forhigh pressure systems and 1,800 psi for low pressure systems.Valves which are constantly under pressure in high pressure systemsmust brave a minimum bursting 6,000 psi.

(m) Other characteristics of CO2 piping and fittings are:

i. Corrosion resistance.ii. No combustibility.iii. Withstand temperature extremes that may expect.

(5) Nozzles:

(a) Many types are available.

(b) Those used in total flooding may be just orifices for highvelocity jet streams or partially orifices for high velocity or desireddischarge pattern.

(c) High velocity discharge creates substantial convection mixingto assure uniform concentration of CO2 throughout the enclosure.

(d) Low velocity may give greater concentration in the lowerlevels. This is desirable sometimes.


8/10

190

(e) Nozzle for local application are normally designed for relativelylow discharge velocity, to avoid splashing of liquid fuels land minimizeturbulence and air entrainment.

(f) All such nozzles must be test and approved based on tests.

10. Operation of Systems:

a. Method of Actuation:

(1) Total flooding and local application CO2 systems are designed tooperate automatically or manually: automatic systems must also have anindependent means of manual actuation.

(2) Requirements for automatic operation are:

(a) Reliable means of detecting the fire or dangerous conditions.(b) An actuating device.

(3) Appropriate detection device may one or more of the type of devicesthat will respond to:

(a) Heat.(b) Smoke.

(c) Flame.

(d) Flammable vapors.

(e) Other abnormal process conditions that could lead to fire orexplosion.

(4) Actuation device could be a automatic electric switch to open acylinder valve or could be complicated device involving electrical timingdevice designed to give alarm, shut down equipment, close fire doors, startand stop CO

2flow and other things necessary to extinguish the fire safety and

quickly or correct dangerous situation.

(5) Manual controls, whether as part of an automatic system or the onlymode of operating the system, manual control must be?

(a) Easy to operate.(b) Accessible in case of fire.(c) Located close to the valves they control.

(6) Remote manual controls are usually located near an exit for totalflooding or near hazardous area for local application.

(7) Control valve to manually charge hand hose lines must be positioned

in the immediate vicinity of the hose reel nozzles should be designed forsimple and quick opening and closing.

(8) Hand hose lines can be designed to be charged automatically byraising to nozzle from its holder.

b. Quantity Requirement:

(1) Quantity of CO2 required for extinguishment depends on the following:

(a) Type of fire.

(b) Type of extinguishing system.

(c) Conditions in the fire area that would adversely affect the

successful operation of the system.(2) If continuous protection is required minimum quantity need in twicethat needed for extinguishment.


9/10

191

11. Total Flooding System:

a. Quantity of CO2 required is based on achieving a minimum designconcentration and keeping it until the fire is extinguished.

b. While CO2 is being injected, a mixture of air and vapor equal to the volumeinjected is pushed out. This is known as free effuse flooding.

c. Because of the losses during injection, it takes a greater volume of vapor toreach a given concentration, than the actual volume remaining in the enclosure.

d. The weight of CO2 required is calculated by dividing the volume of vapor landmultiplying by the volume of enclosure. (Specific volume of CO2 9 for normal totalflooding).

e. Most enclosure will have cracks around doors and other nearly invisibleopenings.

f. In small enclosures, the amounts lost through leakage are larger in relativepercentage. Therefore certain flooding factors are made to compensate for leakagein enclosures smaller than 50,000 cu ft.

g. Leakage through openings that cannot be closed must be compensatedbased on estimated loss rate.

h. Surface burning fires are usually extinguished during discharge not longerthan 1 min.

i. Extra CO2 to compensate for leakage through enclosable openings can bebased on a 1 min holding time and is added to the basic quantity.

j. Deep seated fires require higher concentration and extinguishingconcentration must be maintained for a longer time.

k. Rate of discharge must be high enough to ensure a concentration of 30% isreached with 2 min and final design concentration is not more than 7 min. Leakage

compensation is in addition to the basic quantity.

l. Enclosures for deep seated must be relatively tight or concentration.

12. Local Application Systems:

a. Preferably designed using the rate by area method.

b. Rate of discharge from each nozzle is determined from listing information.

c. Total discharge rate for the system is the sum of all nozzle discharge.

d. Required minimum effective discharge time is 30 sec.

e. If the hazard consists of three dimensional irregular objects that cannot be

easily reduced to equivalent surface areas then rate by volume method.

13. Extended Discharge System:

a. Used to compensate for leakage loss.

b. Rate of discharge equals to the rate of leakage.

c. The quantity is based on rate of discharge multiplied by time that theconcentration must be maintained.

d. This is an addition the initial quantity required to develop the designconcentration.

14. Hand Hose Lines:

a. Required quantity depends on:


10/10

192

(1) Type of hazard.(2) Size of hazard.

b. Certain additional amount must be available to compensate for wastage dueto inexperienced operators.

c. Must have enough CO2 to allow operation for at least 1 min.

15. Mobile Supplies. Mobile CO2 supply for fixed systems should be the same as ifthe supply were a fixed part of the system, with an extra quantity to compensate for thedelay in getting the supply to the system standpipe.

16. Supervision of System:

a. More complex systems require greater and close supervision.

b. Minimum, every system should have and audible or visual signal to indicatethat the system has operated and should be places back in service.

c. Audible alarm necessary to warm occupants of discharge areas that anoxygen deficient atmosphere is about to be present.

d. Occupants should have enough time to escape before CO2 is released.

e. Delaying the discharge of CO2 for a time after the alarm has sounded may benecessary.

f. Extensive and complicated detection and control system and cannot bevisually checked then and automatic supervisory system should be arranged togive immediate and positive indication of any failure.

17. Maintenance, Inspection and Test Procedures:

a. Frequent scheduled visual checks.

b. Tests at least once a year.c. In order to run a satisfactory test, may be necessary to discharge enough CO2to operate all pressure actuated parts of the system.

d. Weigh Cylinders at least once in 6 months for loss through leakage.

e. Loss of weight by 10% or more, replace cylinder.

f. Replacement of CO2 cylinders not immediately possible additional CO2cylinder should be kept on hand.

Fix Installation (CO2)

Documents

Transcript of Fix Installation (CO2)