USING DRY CHEM ON CLASS B FIRES
BY KEVIN S. ELMORE
Recently, firefighters at the Indianapolis International Airport conducted a live fire training session using the dry chemical potassium bicarbonate as the primary extinguishing agent. It was expelled by dry nitrogen on an E-One Titan III crash truck. Five hundred pounds of agent were used to combat a Jet A fuel fire involving approximately 300 gallons. The training session pointed out some reminders to experienced firefighters and helped to educate younger firefighters in the art of chemical extinguishing agents.
Of the many types of dry chemicals in use today, potassium bicarbonate is perhaps the most commonly used. This purple compound, commonly called Purple K, has been widely used by the military for years and is used by most airport fire departments. Many departments use it for liquid fuel fires because of its ability to extinguish Class B fires, its compatibility with aqueous film forming foam (AFFF), and its relatively low cost. Although a powder, this agent should not be confused with dry powder extinguishing agents used on combustible metal fires.
Using Purple K has advantages and disadvantages, and both were pointed out by firefighters participating in the training session. When used to extinguish pooled liquid fuel fires, this agent provides a rapid knockdown with relative ease. Two firefighters using a one-inch booster hose brought the fire under control in 30 to 45 seconds. Complete extinguishment was accomplished in approximately two minutes.
ASSESSMENT
The smaller handline is certainly lighter and easier to maneuver, but this advantage may be outweighed by the need to rapidly move the nozzle. In this scenario, liquid fuel pooled in a contained area and was easily extinguished. However, this agent`s greatest strength may be its ability to extinguish running fuel fires.
Many firefighters are not surprised to hear that self-contained breathing apparatus (SCBA) must be used with this dry chemical, since the cloud emitted from the nozzle is an irritant when inhaled. Some firefighters, however, may not know that Purple K can also be absorbed through openings in the skin. Soft tissue wounds are particularly vulnerable. The sensation felt on skin contact is similar to that felt when tomatoes contact open mouth sores.
Using dry chemicals to fight fires takes practice, as does the use of any other extinguishing agent. Nozzlemen must be aggressive in applying the agent and must constantly watch for flashbacks. Potassium bicarbonate extinguishes fire by interrupting the combustion chain reaction, among other things (it does not cool hot fuels to any great extent). Once the fire is extinguished, the hot fuel vapors can be easily reignited, and responders must keep a constant watch for flashback. A nozzle must be in place and ready for rapid movement to prevent this condition from developing.
Another factor that must be taken into consideration concerning the use of dry chemical systems on apparatus is the reservicing of these units. It is a cumbersome and messy detail. In a number of units, the storage tank for the chemical is mounted inside the vehicle body on the chassis. Access is gained through an opening on the roof. The tank is refilled by manually dumping 50-pound buckets of dry chemical into the tank one at a time. The buckets are approximately five gallons in size. Each container must be dumped into a strainer mounted on top of the tank. This process prevents large chunks of chemical from entering the tank and serves to sift the agent. High volumes of chemical dust are created during this process, and respiratory protection is a must. Additionally, once the task has been completed, everything in the vicinity will have to be cleaned of the powder. Dry nitrogen is used to expel the chemical from the tank. The dry nitrogen tank is mounted on top of the vehicle near the water tank opening. Replacing this unit is not easy. It can be hydraulically removed and replaced by using an overhead crane or forklift. If necessary, it can be removed by personnel alone using the vehicle`s rear steps. Compressed air should not be used for this application, since it has a tendency to accumulate moisture and will cake the powder. Reservicing time for this particular session was approximately one and one-half hours. This included expelling one additional tank of nitrogen through the system to flush it of caked or packed chemicals. Certainly, crash fire apparatus manufacturers need to improve this system.
One final concern is the dry chemical`s packing or caking inside storage tanks. Over the years, fire officials have expressed this concern. In fact, numerous agencies have required periodic stirring or agitating of the agent to prevent this. As a result, silicone has been added to the chemicals to prevent this problem. According to the manufacturers, stirring or shaking these chemical tanks is no longer necessary. No caking or packing problems occurred during this session, and the chemical had been in the tank for more than one year with no specific agitation of the tank. n
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Dry chemical systems have an effective range for operations.
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When first applying a dry chemical agent, the discharging action pushes the fire back.
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Air must be expelled from the line before discharging the dry chemical agent.
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The dry chemical will put a fairly heavy cloud of agent over the fire when properly applied. SCBA use is essential when using dry chemical.
KEVIN S. ELMORE, a 20-year veteran of the fire service and a retired USAF firefighter, is a member of the Indianapolis International Airport Fire Department. He a nationally certified Fire Service Instructor III, Fire Officer II, Fire Inspector II, and Airfield Firefighter.
You must be ever vigilant for flashbacks when using dry chemicals to extinguish a fire. (Photos by Yvonne Carter.)
