Chapter 10

© 2008 Delmar, Cengage Learning

Gaseous Agent Extinguishing Systems

Chapter 10


Learning Objectives

• Describe the physical characteristics of carbon dioxide

• Describe the four application methods of delivery for carbon dioxide

• Explain the reason for and the impact of the Montreal Protocol

• Describe the physical characteristics of halogenated hyrdrocarbons (halons)


Learning Objectives (continued)

• Explain the halon numbering identification system

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

• Name the two categories of clean agents


Introduction

• Alternative fuels were developed to cope with new manufactured materials

• Environment, logistics, technological application may make it impractical to use water

• Necessary to prevent water damage to extremely valuable property

• Extinguishing gases offer an alternative • Three types of gases: carbon dioxide, halons,

and clean agents


Carbon Dioxide• Odorless, colorless, noncombustible, and

nonconductive• Exists in air at a very small level

– Approximately 380 parts per million by volume

• Displaces and reduces the level of oxygen below 15% of the air content

• 50% heavier than air, and separates air from the fuel as it extinguishes the fire

• Not suitable for reactive metals, materials containing oxygen, metal hydrides


Carbon Dioxide Fire Extinguishing Systems

• Self-contained and use fixed nozzles, manual hose reels, or both

• Highly pressurized CO2 liquid expands to a gas vapor state, combines with moisture in the air– Forms a fog-like cloud that consumes the hazard

• Cloud quickly dissipates, but gas lingers to maintain non-ignitable environment

• Useful where clean up of another agent would be problematic


Low- and High-Pressure Storage

• Two types of carbon dioxide extinguishing systems:– Low-pressure storage: stores about 300 psi– High-pressure storage: stores above 850 psi

• Both high enough to make CO2 self-expel

• Low-pressure systems require refrigeration/heating equipment

• Activation may be automatic, manual, or emergency manual


Figure 10-1 Low-pressure carbon dioxide extinguishing system protecting a chemical storage facility


Carbon Dioxide Delivery Systems• Local application systems protect a specific

area• Total flooding systems protect enclosed

hazards, rooms, and areas within a structure– Fill entire enclosure with CO2

• Hand hose system are manual delivery– Individual accesses a hose, real, and nozzle

• Standpipe/Mobile supply systems installed at industrial facilities– For use by trained personnel


Halogenated Agents• Halogenated hydrocarbons: mixture of carbon

and one or more halogen elements– Also called halon

• Numbering system indicates chemical makeup– Halon 1211: 1 part carbon, 2 parts fluorine, 1 part

chlorine, 1 part bromine– Halon 1301: 1 part carbon, 3 parts fluorine, zero parts

chlorine, 1 part bromine

• Halon 1211 and 1301 are only two halons in widespread use in fire systems


Halon Fire Extinguishing Agents

• Odorless, colorless, non-corrosive, nonconductive, nontoxic at low concentrations– Leave minimal residue

• Halons break down the reaction sequence of fire• Effective on Class B and C fires• Protect computer rooms, electronic equipment,

flammable and combustible liquids, etc.• Not suitable for reactive metals, materials

containing oxygen, metal hydrides


Halon Extinguishing Systems

• Pre-engineered or engineered, self-contained• To start sequence, automatic detection,

activation, and manual controls required• Emergency release by a single manual

operation, appropriate warning devices required• Manual abort switch must be located within the

hazard area– Requires constant pressure to maintain abort status– Time delay allowable when people must evacuate


Halon Delivery Systems

• Two types of halon delivery systems:– Local application– Total flooding

• Same types of systems that protect CO2, wet, and dry chemical systems

• Type of system installed determines the type of halon used

• Most halon systems are total flooding type


Figure 10-4 These storage tanks are a part of a total flooding halon extinguishing system


Location Application Systems• Protect specific areas by discharging halon

directly onto the hazard• Appropriate when enclosing a hazard is not

possible or practical• Nozzle placement and type critical to ensure

appropriate application of the agent• Halon 1211 is a liquid stream agent; best for

local application delivery• When discharged, agent expands as a mixture

of liquid droplets and vapor


Total Flooding Systems

• Protect enclosed hazards by filling the entire enclosure with halon

• Amount of halon and number of nozzles needed depend on total volume of the area

• Concentration levels range from 4% to 15% by volume

• Halon 1301 more appropriate for total flooding systems

• Once discharged, uniform and rapid distribution


Clean Agents• Halocarbons or clean agents are

environmentally safe, non-toxic, not electrically conductive; leave no residue

• Effective on Class A, B, and C fires• Protect computer rooms, telecommunication

facilities, radio and television broadcast, etc.• Possibility of health problems if exposed for an

extended time at high concentrations• Exposure during fire may subject a person to

higher levels of byproducts than with halon


Categories of Clean Agents• Clean agents fall into inert gas-based category• Extinguish by interrupting the chain reaction or

removing the heat from the reaction zone• Inert agents reduce the oxygen level in

protected area• Five subcategory designations:

– FC, FK, FIC, HFC, HCFC– Identify the chemical composition of the mixture

• Inert gases have designation IG– Mixture of helium, neon, argon, nitrogen, CO2


Clean Agent Extinguishing Systems

• Only application method is total flooding• System activation operates a discharge control

head and valve– Allows gas to escape the cylinders, flood the piping

and flow to nozzles

• Substantial discharge of the agent:– Within 10 seconds of activation for halocarbons– Within 60 seconds for inert agents


Approval and Periodic Inspection, Testing, and Maintenance

• All carbon dioxide, halon, clean agent systems must go through periodic inspection, testing, and maintenance


Carbon Dioxide• Once installation complete, NFPA 12 requires

visual, operational, discharge inspections and tests

• When system is operational, weekly and monthly visual inspections:– Prevent conditions that prevent proper operation– Determine if there have been changes in the hazard– Determine if there is equipment damage or signs of

system leaks

• Liquid level and pressure on low-pressure systems requires checking


Halon

• NFPA 12B, the standard for halon 1211, is obsolete

• Ten-minute pneumatic pressure test determines if there is pipe leakage

• Puff test ensures piping continuity• Enclosure integrity test determines amount of

leakage from the enclosure• Concentration level should be at least 80% of

design amount after 10 minutes


Clean Agents

• Visual inspection verifies components are correctly placed, and all signage is in place

• Operational testing verifies mechanical and electrical components perform as required

• Ten-minute pneumatic pressure test determines if there is pipe leakage

• Puff test ensures piping continuity• Significant leakage will reduce the concentration

to below an acceptable level


Figure 10-8 A Test equipment used to determine the amount of air leakage from the enclosure


Summary• Alternative extinguishing agents developed for

new manufactured materials• Gaseous systems are self-contained,

engineered, or pre-engineered systems• Gases work well on Class A, B, and C type fires

– Not suitable for reactive metals, materials containing oxygen, metal hydrides

• Halons no longer manufactured for environmental reasons– Clean agents work well as halon substitutes

Chapter 10

Business

Transcript of Chapter 10