ch10 gaseous agent extinguishing systems

Chapter 10Gaseous Agent Extinguishing Systems

Objectives • Describe the physical characteristics of

carbon dioxide. • Describe the four application methods for

delivery of carbon dioxide.• Describe the physical characteristics of

halogenated hydrocarbons (halons).

Objectives

• Explain the halon numbering identification system.

• Describe the physical characteristics of halocarbons and inert gases (clean agents).

• Discuss the two categories of clean agents.

Objectives • Explain the difference between the two

types of aerosol generators. • Discuss the various acceptance and

periodic inspections and tests that are required to certify and maintain gaseous agent extinguishing systems.

Introduction • New materials, machines, processes, and

technologies created a need for alternatives to water for extinguishing.

• Gaseous extinguishing systems are effective in many situations where water is not.– Carbon dioxide– Halogenated hydrocarbons– Halocarbons and inert gas

Carbon Dioxide • An odorless, colorless, noncombustible gas

– Exists in the air at 380 parts per million– Can exist as gas, solid, or liquid

• Liquid state best for suppression– Effective on Class A, B, and C type fires

• Displaces and reduces the level of oxygen below the 15% of air content that is necessary to sustain combustion

Carbon Dioxide Extinguishing Systems

• Engineered systems that protect processes, equipment, items of value/importance

• Self-contained system using fixed nozzles, manual reels, or both to deliver agent

• Equipment requires listing or approval.


• When discharged pressurized CO2 expands to gas vapor state:– Combines with moisture in air and forms a

cloud that consumes hazard• Helpful when another agent could be

problematic or there are physical obstructions


• A few types of systems and methods exist.– Chosen based on hazard size and amount of

agent needed• Many different nozzles are available to

provide the correct discharge velocity, flow rate, and discharge pattern.


• Discharge nozzles– Must be able to

withstand fire’s heat and discharge pressure of CO2

– Require blow-off caps or frangible discs to manage clogging

– Require listing or approval © A. Maurice Jones, Jr./Jones & Bartlett Learning


• Activation– Automatically with a detector OR manually by

a person– Warning signs must be posted about dangers

and give emergency instruction.• Guidance on performing the evaluation,

design, and installation of this type of system is in NFPA 12.


• Low- and high-pressure storage– Low pressure stores CO2 at 300 psi; high

pressure at 850 psi.• Both systems dispel gas without additional

propellant.• System type is chosen based on hazard and amount

of CO2 needed.

– Low-pressure systems may need refrigeration/heating equipment to maintain CO2

at 0ºF.


• Low- and high-pressure storage (cont’d)– Low-pressure systems

may use one large pressure container.

– High-pressure systems can use multiple small cylinders connected to a manifold.

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© A. Maurice Jones, Jr./Jones & Bartlett Learning


• Delivery systems– Local application systems protect a specific area, piece

of equipment, process, or operation.– Total flooding systems protect enclosed hazards,

rooms, and areas, filling enclosure with gas.– Hand hose line system is manual system where

individual accesses hose, reel, and nozzle connected to fixed pipe CO2 supply.

– Standpipe/mobile supply is a fixed local, total, or hand hose system with no permanent CO2 supply.

Halogenated Agents • A mixture of carbon and one or more of fluorine,

chlorine, bromine, and iodine– Numbering system lists number of atoms of each element

in the agent.– Halon 1211 and 1301 are used for fire protection.

• Halon agents break down the reaction sequence of fire. – Disrupting the uninhibited combustion reaction that is the

basis of the fire tetrahedron– Effective for Class B and C type fires, and Class A to a

degree

Halogenated Agents • Human exposure is okay, unless high level

or long duration.– Most systems have 4% to 7% concentration.

• 10% or higher is dangerous to humans.– Fire personnel should wear SCBA and take

readings in discharge areas.• Decomposition produces dangerous by-products.

Halon Extinguishing Systems • Can be pre-engineered or engineered and

use many components• All equipment and components require

listing and approval.

Halon Extinguishing Systems • Automatic detection and activation and

manual control are usually required.• Must also have emergency release by

manual operation and audible, visual, and olfactory warning devices

• When activated, control head operates and valve head opens to release gas to cylinders, flood piping, and reach nozzles

Halon Extinguishing Systems • If manual abort switch

is installed, must be in hazard area.

• Substantial discharge must occur in 10 seconds.– Time delay allowed for

personnel to evacuate– Warning signs

required © A. Maurice Jones, Jr./Jones & Bartlett Learning

Halon Extinguishing Systems • Nozzle placement is critical to uniform delivery.

– Pressurized nitrogen can be added.• Halon changes from liquid to vapor as it flows.

– Discharges as cloud; when cloud dissipates, gas remains

• Once the hazard evaluation is done, there are engineering considerations.– Size and number of cylinders and size of pipe– Nozzle and valve types

Halon Extinguishing Systems • NFPA 12A gives guidance on evaluation,

design, and installation of this type of system.– Referenced by NFPA 5000 and IBC

• NFPA 12B (Halon 1211) was discontinued.– NFPA 12A may also become obsolete.

Halon Extinguishing Systems • Halon delivery systems

– Local application systems protect specific area.

• Discharge directly onto hazard– Total flooding systems protect

enclosed hazards by filling them with halon.

• Concentration level: 5–15% by volume

– Halon 1301 is usually the only agent used for these systems.


Clean Agents • Clean agents were developed to replace

Halon 1301.– Effective on Class A, B, and C fires– Protect many high-value locations and items– Should not be used with reactive materials,

materials with own oxygen supply, certain peroxides and hydrazine

Clean Agents • Human exposure ok, unless high level or

long duration• Clean agents fall into two categories:

• Halogen-based agents interrupt the fire’s chain reaction and remove heat from reaction zone of flame.

• Inert agents reduce oxygen level in protected area.

Clean Agent Extinguishing Systems

• Pre-engineered or engineered self-contained systems that use a number of different components

• All equipment and components require listing and approval.– Specific to application


• Automatic detection and activation and manual control usually required

• Must also have emergency release by manual operation and audible, visual, and olfactory warning devices

• If manual abort switch installed, must be in hazard area


• When activated, control head operates and valve head opens to release gas to cylinders, flood piping, and reach nozzles.


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• Substantial discharge must occur in 10 seconds for halocarbons and 60 seconds for inert agents.

• Warning signs with emergency information must be posted.


• Nozzle placement is critical to uniform delivery.– Clean agents can flood an area

and reach difficult places. • Once the hazard evaluation is

done, there are engineering considerations.– Size and number of cylinders– Pipe size



• NFPA 2001 gives guidance on evaluation, design, and installation of this type of system.– Referenced by NFPA 5000 and IBC

• Additional standards:– UL 2127– UL 2166– ISO 14520-1

Aerosol • A chemical fire extinguishing agent

– Begins as a potassium-based compound– Undergoes internal combustion process and

becomes ultra-fine spray• Similar to halon and clean agents—interrupts

fire chain– Once discharged, remains in environment long

enough to prevent reignition– Best for Class B and C fires, but can be used for all

Aerosol Fire Extinguishing Systems

• Alternative to clean agent and specialized water-based systems– Good for closed spaces and areas appropriate

for total flooding– Per NFPA 2010, not well suited for:

• Deep-seated fires• Chemicals subject to rapid oxidation• Reactive metals• Chemicals that undergo autothermal decomposition

Aerosol Fire Extinguishing Systems

• Condensed generators– Used in systems made up of self-contained canisters in

the hazard area– When activated, an actuator in the generators starts a

chemical reaction.• Dispersed generators

– Already contain the chemical agent– Keep it pressurized by suspension in inert gas or

halocarbon– When activated, pipes and nozzles distribute aerosol.

Approval and Periodic Inspection, Testing, and

Maintenance • Carbon dioxide

– After installation NFPA requires visual, operational, and discharge inspections and tests.

– Once operational, monthly visual inspections to assess hazard changes, equipment damage, leaks

– Weekly inspection of gauges on low-pressure systems to ensure no decrease in liquid level

– Semi-annual inspection of high-pressure system tanks to ensure no leakage


Maintenance • Carbon dioxide (cont’d)

– Annual actuation test of electronic components for both low- and high-pressure systems

– Hose systems inspected and pressure checked every 5 years

– When system discharges, tanks require hydrostatic testing before refilling.

– If unused for 12 years, discharge and hydrostatic testing are required.


Maintenance • Halon

– When new Halon 1301 system is installed, mechanical, electrical, enclosure, and functional testing and inspection are mandatory.

– Once operational, monthly visual inspections to assess hazard changes, equipment damage, leaks

– Semi-annual pressure checks to ensure pressure not lost


Maintenance • Halon (cont’d)

– Annual actuation test to ensure detection, alarm, and control devices are operational

– Annual inspection and pressure testing every 5 years for hose systems


Maintenance • Clean agents

– Upon installation, same procedures as halon systems

– Once operational, annual visual inspections– Semi-annual pressure loss checks– Annual actuation test– Annual inspection and pressure testing every

5 years for hose systems


Maintenance • Aerosol

– Like other systems, acceptance inspection and testing and periodic testing are mandatory.

– 30-day visual inspection and semi-annual weighing

– Enclosure and system components checked– System tested as specified by manufacturer

Summary• Alternative extinguishing agents are needed

to deal with fires where the use of water could make the situation worse or damage extremely valuable or irreplaceable property and equipment. Gas-based extinguishing agents—in particular, carbon dioxide, halons, halocarbons, and inert gases—offer viable, effective alternatives in many environments and applications.

Summary• Gaseous systems are self-contained

engineered or pre-engineered that use similar components, including nozzles; piping; containers; control panels; detection, activation, and alarm devices; control valves; and releasing mechanisms.

• Gases work well on Class A, B, and C type fires, but not fires involving reactive metals, materials containing their own oxygen supply, or metal hydrides.

Summary• Gaseous system design requires

extensive evaluation of the hazard to ensure the right agent is used and concentration level is adequate.

• The main application methods are local application and total flooding.

Summary• When discharged, carbon dioxide

displaces the oxygen in a protected area. If a person fails to leave the area, asphyxiation is probable.

Summary• Due to environmental concerns, toxicity

concerns, and the requirements of the Montreal Protocol, halon agents are no longer manufactured and the continued phase-out makes the agents difficult to obtain and systems nearly obsolete.

Summary• Clean agents work well as halon substitutes,

but none can directly replace halons; exposure during a fire subjects the individual to higher levels of dangerous decomposition by-products than with halon.

• To ensure performance and reliability, all gas-based fire suppression systems require acceptance inspection and testing, and periodic inspection, testing, and maintenance.

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