CARBON DIOXIDE FLOODING SYSTEM:-
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Broadly speaking, there are two methods for applying an extinguishing agent:
1) Total Flooding
2) Local Flooding
Systems working on a total flooding principle apply an extinguishing of the agent to a three dimensional enclosed space in order to achieve a concentration of the agent (volume percent of the agent in air) adequate to extinguish the fire. These types of systems may be operated automatically by detection and related controls or manually by the operation of a system actuator.
The main difference in local application from total flooding design is the absence of physical barriers enclosing the fire space.
Carbon dioxide Extinguishing Agent:-
CO2 has been I'm widespread use for may years and is likely to have safely extinguished more fires than any other gaseous fire-extinguishing agent. In the process, carbon dioxide systems have saved lives, maintained livelihoods, and prevented property damage. The benefits of carbon dioxide systems, properly applied, are enormous. To gain the benefits of carbon dioxide extinguishing systems while minimizing risk to people, serious attention must be give to personnel safety in the design, installation, and maintenance of carbon dioxide systems. Training of personnel is essential.
This blog will discuss the properties of carbon dioxide and it's proper use in fixed fire-extinguishing agent; life safety consideration; methods of application; system components ; design considerations; and requirements for testing, maintenance, and training. NFPA 12, Standard on Carbon Dioxide Extinguishing Systems, provides guidance to those responsible for the purchase, design, installation, testing, inspection, operation, and maintenance of carbon Dioxide systems.
Applications:-
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CO2 has been used for many years to extinguish flammable liquid fires; gas fires; fires; involving electrically energized equipment;and to a lesser in an ordinary combustibles, such as paper, cloth and other cellulose materials. Carbon Dioxide will suppress fire effectively in most combustible material. Exceptions are a few active metals and metal hydrides, and materials, such as cellulose nitrate, that contain available oxygen. Furthermore, practical limitations of carbon dioxide is a very effective extinguishing agent for
•Ordinary Combustibles -Class A fires
•Flammable Liquids- Class B fires
•Electrical Hazards- Class C fires
In some isolated circumstances, ordinary combustibles may be amenable to the use of a carbon dioxide system, but in most cases a standard sprinkler system is more effective and less hazardous to personnel. Record storage rooms containing rare or irreplaceable documents may require a gaseous system to avoid water damage. Dust collectors, grain elevators, and food milling machines may be amenable for protection by a carbon dioxide system.
Some flammable liquid hazards are commonly protected by carbon dioxide systems.
Examples of such applications include:
•Open top lube oil pits- open pits for storage of lube oil for lubrication of power plant turbine generators.
•Industrial Fryers, range hoods, and grease ducts
•Dip thanks containing flammable liquids for planting or stripping or mental components
•Marine engine protection.
•Solvent storage rooms
•Printing presses and folder flammable ink, lubricating oil, and paper dust.
• Paint spray booths and paint storage rooms.
•Chemical Storage labs
•Flammable Liquid storage
•Test cells for aircraft engine testing.
A carbon dioxide system may be ideal for protecting electrical hazards because carbon dioxide does not conduct electrical charges. The pipe systems and the nozzles must be grounded to avoid the transfer of electrostatic charges resulting from frictional resistance at the nozzles.
Electrical applications include:
•Electronic data processing- computer room or protection of subfloor below computer room
•Turbine generator enclosures
•Electric switchgear rooms.
•Battery Storage rooms.
•Electrical Cabinet interiors
•Wave solder machinery- enclosures where tin cans are soldered shut or where electronic components are manufactured.
General Properties of Carbon Dioxide:
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Carbon dioxide has a number of properties that make it a desirable fire-extinguishing agent. It is not combustible, it does not react with most substances, and it provides it's own pressure for discharge from the storage container. Since carbon dioxide is a gas, it can penetrate and spread to all the parts of the fire area. As a gas or as a finely divided solid called "snow" Or "Dry Ice", it will not conduct electricity it is therefore used and energized electrical equipment. It leaves no residue, thus eliminating cleanup of the agent itself.
Extinguishing Properties of Carbon Dioxide:-
The primary mechanism by which carbon dioxide extinguishes fire is oxygen reduction(Smothering). The cooling effect of carbon dioxide is relatively small but does make some contribution to fire extinguishment, particularly when carbon dioxide is applied directly to the burning material.
General Safety Guidelines:-
To gain the benefits of carbon dioxide extinguishing systems while minimizing risk to people, serious attention must be given to personnel safety. Personnel safety must be considered in the design, installation, maintenance, and use of carbon dioxide systems. NFPA12 Discusses personnel safety at length.
Total flooding carbon dioxide should not be used in normally occupied spaces unless arrangements are made to ensure evacuation before discharge. The same restriction applies to spaces that are not normally occupied but in which personnel might be present for maintenance or other purposes. It can be difficult to ensure evacuation if the space is large or if egress is in any may impeded by obstacles or complicated passageways.Escape is even more difficult after the discharge starts, because noise, greatly reduced visibility, and the physiological effects of the carbon dioxide concentration can overwhelm the occupants.
Consideration also should be given to the possibility of large volumes of carbon dioxide vapour leaking or flowing into unprotected lower levels, such as cellars, tunnels, or pits. Periodic maintenance is required to ensure proper function of these systems. Those doing maintenance be thoroughly trained in the functions of the system. Whenever maintenance involves work on system controls, discharge valves, or other devices work on system controls, discharge valves, or other devices that could possibly initiate carbon dioxide, personnel must be evacuated from the protected space.
Limitations of carbon dioxide:-
The use of carbon dioxide on general class A fire is limited by its relatively low cooling capacity, compared to that of water, and by enclosures incapable of retaining an extinguishing atmosphere. True surface burning fires are extinguishing easily because natural cooling takes place quickly. On the other hand, if the fires penetrates below the surface of the fuel and the mass of fuel provides a layer of thermal insulation.
Heat loss(generally referred to as "deep-seated burning"), a higher concentration of carbon dioxide and a much longer holding time are needed for complete extinguishment. Some deep seated fires may not be extinguished by carbon dioxide can be used to supress open flaming and slow enough to permit response by a properly equipped and trained fire Brigade.
Carbon dioxide is not an effective extinguishing agent for fires involving chemicals that contain their own oxygen supply, such as cellulose nitrate. Fires involving reactive metals, such as sodium, potassium, magnesium, titanium, Zirconium and the metal hydrides, cannot be extinguished by carbon dioxide because the metals and hydrides decompose carbon dioxide.
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