Class D fires require a unique application technique. Unlike Class A or Class B fires, you will not see a lot of flame or feel a lot of radiant heat in the early stages of the fire. There will be intense light in the case of magnesium, volumes of dense smoke from lithium, and very little smoke with either titanium or zirconium. But don’t let the small size of the fire or the lack of flame fool you. These are serious fires and the potential for disaster exists if you or your customers underestimate them.
Burning Class D material generates hydrogen gas when it is exposed to water causing a violent explosion. Moisture in the ground, concrete, or even in some agents themselves may cause this reaction. Therefore, extreme caution must be used when fighting these fires.
The control of these fires is achieved by attacking two fronts simultaneously: excluding oxygen from the combustible metal by completely surrounding it, even what isn’t yet burning, and by the absorption of heat to below the temperature required to sustain the fire. This latter feature of Class D agents is frequently referred to as “heat sink”.
The principle of extinguishment is to completely cover the burning material with a layer of Class D agent up to 2 inches thick. After using the unique Amerex applicator wand to cover the material and while standing ready to reapply agent as burn through “hot spots” appear. It is best to use either the agent remaining in the fire extinguisher or to utilize the scoop and pail to prepare to seal the underside of the burning material. Forgot about that didn’t you? How do you get the burning material that is already in one spot on top of the 2-inch bed of agent? After discharging or shoveling agent onto the floor near the burning material carefully use a clean, dry shovel to move the pile of agent encrusted combustible metal. Gently lay this on top of the bed of agent, return to the extinguisher or scoop and continue applying agent to any cracks that appear in the crust or cover any new hot spots that appear to be burning through. Do not rush to cleanup! Remember even without hot spots the fire may still be burning deep below the surface. Always use extreme caution and patience. Make sure the fire is completely out before attempting cleanup procedures.
While many fire fighting exercises are uncomplicated, the nature of this type of material – high temperature, moisture sensitivity, fine particles easily spread, tendency to generate toxic gases or smoke – make Class D fire training critical. While Class D fire fighting may not ultimately be complicated, it is certainly very detailed requiring exacting procedures!
Remember the operating instructions on the extinguisher “CAUTION: FIRE MAY RE-IGNITE, ALLOW METAL TO COOL BEFORE CLEANUP”.