Carbon Dioxide (CO2)
Fire Suppression Systems
Norb Makowka, NAFED Technical Director
Carbon dioxide has been recognized as a fire extinguishant for many years. It has been used in fixed systems since before World War I and almost everyone in the fire protection community has used or seen used a hand portable CO2 fire extinguisher. Even so, the system applications for CO2 are not widely understood and, in fact, may be very much misunderstood.
Many may think that CO2 is an extinguishant that, for the most part, has been replaced by Halon 1301 or the new alternate clean agents such as FM-200 or Inergen. You may think that CO2 and the other clean agents compete for the same market. This is generally not the case. Therefore, I would like to outline some of the applications for CO2 fixed systems in generic terms to give you a better understanding of the potential applications for CO2 fire suppression systems.
Let's first look at the characteristics of CO2 as they apply to fire extinguishment and then relate these to system applications.
CO2 as an Inert Gas
CO2 is an inert gas, it is a relatively inxpensive gas, commonly available and quite easy to handle. Inert gases have the ability to prevent fires and explosions by inerting combustible atmospheres.
Application Example: A coal pulverizer - when it is started and coal is added, there is a point when the suspended coal particles and the air are in the explosive range. The same condition exists on shut down as coal is removed.
CO2 can make this start up and shut down safe by inerting the air/coal mixture and preventing an explosive atmosphere.
Application Example: The generator of a power plant turbine generator is hydrogen cooled. The hydrogen cannot be introduced into a generator full of air without going through the explosive range. It can't be removed and the unit ventilated without passing through the explosive range the other way. CO2 introduced in each cycle acts as a buffer never allowing the proper mixture of air and H2 to create an explosive atmosphere.
CO2 as an inert material can be introduced into a mass of solid burning material to reduce the burning rate and effect extinguishment.
Application Example: The reactive coal from the West is highly susceptible to spontaneous ignition. Small coal particles in a storage silo start to heat and, unless used quickly, will start to burn. The burning is buried in the mass of coal. It is very difficult to get water to this type of fire. CO2 vapor can be introduced, forced between the voids of the coal to the burning mass and, by eliminating the oxygen, reduce the burning rate until the mass slowly cools and the fire controlled.
CO2 as a Dry Chemical
CO2 is stored under pressure as a liquid. When it expands from storage pressure to atmospheric pressure, it "flashes" into CO2 vapor and to fine particles of dry chemical which is really solid CO2 or "dry ice." These particles have a mass which can be projected. The particles also sublime (change from solid to gas) when they pick up heat. So they clean themselves up.
Application Example: The amount of dry ice in a CO2 discharge is a function of the storage temperature. In the storage range of 70 degrees F. down to 0 degrees F., the percentage of CO2 discharged as dry ice from a liquid CO2 discharge will vary from 18% to over 45% depending on storage temperature but, since CO2 is economical, large quantities can be used. The ability to project the dry ice allows extinguishment at distances removed from the nozzle. The CO2 is not a conductor of electricity and will not break down under continuous electric arcing so it works well around electrical equipment.
In fixed system applications, hand hose lines can be used by themselves or used as an adjunct to automatic protection. In either case, they are generally served by a relatively large CO2 supply so that they can be discharged for long periods of time (many minutes) so as to attack stubborn fires such as burning electrical insulation.
The CO2 eventually all turns to gas, which is a three dimensional agent. Therefore, it can be applied in a pit, trench, vault, etc. and extinguish the fire without the need to directly apply the agent.
CO2 as a Locally Applied Extinguishing Agent
Gaseous fire extinguishants are generally thought to be applicable where the hazard area can be "totally flooded". CO2 is not generally used as a total flood agent except in circumstances discussed below. Rather, it is used in the local application form to cover a piece of equipment or a process where the area of its use is too large for flooding and a clean agent is mandatory.
Application Example: Aluminum and some other metals are reduced in thickness and shape by processing through a rolling mill in which the heat generated is removed by a flammable liquid such as kerosene. Kerosene is used to retain the bright finish and to lubricate the metal as it is rolled. The use of water in such an application is absolutely unacceptable.The oil vaporizes as it is heated and fires are common. Quick, effective extinguishment ensures continuous production. The local application of CO2 directly to the mill, pits, bearings, coolant system, fume exhaust hoods, etc. works extremely well and has proven to be an effective extinguishing media.
Application Example: The printing of a newspaper involves high speed presses
which generate considerable highly flammable paper lint which, along with the mineral oil of letterpress and offset inks and solvents used for cleaning, presents a ready fire hazard. The coverage of the presses, color units, folders, press drives, etc. with a local application of CO2 ensures that the newspaper is published on time.
CO2 as a Specialized Total Flooding Extinguishing Agent
Where there is a considerable amount of combustible that is of the type in which burning can be quickly deep seated, (burns down into the combustible with the burning mass isolated and insulated by charred remains), a high concentration of agent is needed to effect extinguishment. CO2 being relatively cheap can be used in concentrations of 65% - 75% by volume and still be cost effective.
Application Example: The dead storage in boxes of vital records or important and valuable artifacts that would be severely damaged by water.
CO2 is recommended for total flooding in areas which are not normally occupied and where the nature of the hazard or the economies favor its use.
Application Example: Drying Ovens. Many products are processed by passing through a drying oven and any spillage onto the heating elements or an equipment malfunction could cause a fire which can shut down the facility. CO2 flooding with the higher discharge quantities spelled out in NFPA Standard No. 12 is the answer: Fire extinguished - product and equipment are not damaged by the discharge.
Application Example: Fume Exhaust Systems. The distribution of CO2 throughout a complex duct, filter system is easily engineered and performs well especially at the 65% concentration spelled out in NFPA No. 12.
Application Example: The very large paint mix/storage rooms of a modern automobile assembly plant can have volumes of 350,000 to 500,000 cubic feet. With the automated operation of such facilities, CO2 flooding as the first line of fire defense backed up by water is again very cost effective.
The above are a few of the important features of CO2. Remember its use as an inert gas, applications using local application of the discharge, hand hose lines and specialized total flooding offers an effective fire suppression tool.
Some of the other applications for CO2 systems include auto engine and transmission test, automotive products research, machinery and chip reclamation, heat treating, metal coating and embossing, hydraulic presses and similar machinery, electric motors and generators (enclosed and non-enclosed) for drives or power generation, emergency diesel generators, gas turbines, steam turbine lube and hydraulic systems, paint dipping, flow coating and spraying, snack food cooking, electric furnace transformer vaults, switch gear, electrical cable areas, battery rooms, relay rooms, fume exhaust systems, solvent recovery systems, package printing, laminating, hydro electric including pumped storage, trash burning energy recovery plants, building under sidewalk transformer vaults, can coating, dust collectors, rolling mill lube systems, aircraft engine test cells, film and paper coating, adhesive application, shipboard applications including engine room, cargo holds, etc.
If the hazard needs a clean agent which can be used where personnel are not at risk, Carbon Dioxide is very likely a good fire protection choice.
Posted December 8, 1994.
Questions to the Author.
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