Dry Chemical Extinguishers
Dry Chemical fire extinguishers use foam or powder pressurized with nitrogen and extinguish by separating the four parts of the fire, preventing the chemical reaction between heat, fuel and oxygen and halting the production of fire-sustaining “free-radicals."
Dry Chemical extinguishers are classified by fire type:
- ABC extinguishers
ABC extinguishers employ multipurpose dry chemicals. They are filled with monoammonium phosphate, a yellow powder that leaves a sticky residue that may be damaging to electrical appliances such as computers.
- BC extinguishers
BC extinguishers are filled with sodium bicarbonate or potassium bicarbonate and leave a mildly corrosive residue which must be cleaned immediately to prevent any damage to materials.
- PK extinguishers
PK extinguishers are used on class B and C fires and are the preferred dry chemical agent of the oil and gas industry. These are the only dry chemical agents certified for use in Aircraft Rescue and Firefighting (ARFF).
Met-L-X is a specialty variation of sodium bicarbonate, along with silica gel particles, for fighting pyrophoric liquid fires (those that ignite on contact with air). The sodium bicarbonate interrupts the chain reaction of the fuel and the silica soaks up any unburned fuel, preventing contact with air.