Fire Detection and Suppression

Chapter 7

Special Extinguishing Systems

Special Extinguishing Systems

Characteristics of Special Extinguishing Systems

Used where automatic sprinklers may not be the best solution to fire problemsHave a limited amount of extinguishing agentMust extinguish fire to be successful

Special Extinguishing Systems

Wet Chemical Systems

Used for commercial cooking hoods, plenums, ducts, and associated cooking appliancesAgent typically solution of water and either potassium carbonate or potassium acetateNFPA 17A, Standard for Wet Chemical Extinguishing Systems

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Special Extinguishing Systems

Wet Chemical Systems (cont.)

Engineered/pre-engineered systemsComponents

Storage tank for expellant gas and agent

Piping to carry the gas and agent

Nozzles to disperse the agent

Actuating mechanism

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Special Extinguishing Systems

Wet Chemical Systems (cont.)

General inspection points

Mechanical damage

Aim of nozzles

Change in hazard

Proper pressures on stored-pressure containers

Check maintenance tag for scheduled service

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Special Extinguishing Systems

Wet Chemical Systems (cont.)

Monthly inspection (to be performed only by trained personnel)

Check that all parts of system are in their proper location and connected.

Inspect manual actuators for obstructions.

Inspect tamper indicators and seals to ensure that they are intact.

Check maintenance tag or certificate for proper placement and information.

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Special Extinguishing Systems

Wet Chemical Systems

Monthly inspection (cont.)

Examine system for any obvious damage.

Check pressure gauges.

Check nozzle blowoff caps, if provided, for damage.

Check that protected equipment or hazard has not been modified, replaced, or relocated.

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Special Extinguishing Systems

Wet Chemical Systems (cont.)

Semiannual inspection (to be performed only by trained personnel)

Ensure that the size or nature of the hazard being protected has not changed.

Examine all components thoroughly.

Check liquid levels of nonpressurized containers.

Verify that the piping is not obstructed.

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Special Extinguishing Systems

Wet Chemical Systems

Semiannual inspection (cont.)

Examine the system for evidence of corrosion, structural damage, or repairs.

Test all working components in accordance with the manufacturers instructions.

Correct any problems noted in accordance with manufacturers recommendations.

Maintenance report and recommendations to be given to a responsible person.

Special Extinguishing Systems

Dry Chemical Systems

Common usesNFPA 17, Standard for Dry Chemical Extinguishing SystemsResidue

Special Extinguishing Systems

Gaseous Systems

Used where wet or dry systems may not be suitableExtinguishing agents

Carbon dioxide (CO2)

Halogenated agents

Halon substitutes

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Special Extinguishing Systems

Gaseous Systems (cont.)

Carbon dioxide extinguishing systems

NFPA 12, Standard on Carbon Dioxide Extinguishing Systems

Personnel safety

System components

Actuation device

Agent storage container

Piping

Nozzles

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Special Extinguishing Systems

Gaseous Systems

Carbon dioxide extinguishing systems (cont.)

High-pressure systems/low-pressure systems

Inspection and testing

Special Extinguishing Systems

Foam Systems

Typically used where water alone may not be effectiveComponents

Water supply

Foam concentrate

Piping system

Proportioning equipment

Foam makers (discharge devices)

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Special Extinguishing Systems

Foam Systems (cont.)

Types

Fixed

Semifixed Type A

Semifixed Type B

High-expansion

Foam/water

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Special Extinguishing Systems

Foam Systems (cont.)

How foam extinguishes fire

Smothering/suppressing: prevents air and flammable vapors from combining

Separating: intervenes between the fuel and the fire

Cooling: lowers the temperature of the fuel and adjacent surfaces

Suppressing: prevents the release of flammable vapors

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Special Extinguishing Systems

Foam Systems (cont.)

Foam generation

Key terms

Foam concentrate

Foam proportioner

Foam solution

Foam

Two-stage process

Proportioning

Aeration

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Special Extinguishing Systems

Foam Systems

Foam proportioners (cont.)

Line eductors

Balanced pressure proportioner

Around-the-pump proportioner

Pressure proportioning tank system

Coupled water motor-pump proportioner

Premixed foam

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Special Extinguishing Systems

Foam Systems (cont.)

Foam nozzles and sprinklers

Solid bore nozzle

Low-expansion foam nozzle

Self-educting foam nozzle

Standard fixed-flow fog nozzle

Automatic nozzle

Foam/water sprinklers

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Special Extinguishing Systems

Foam Systems (cont.)

Foam nozzles and sprinklers

High back-pressure foam aspirator

High-expansion foam generators

Foam system inspection and testing

Special Extinguishing Systems