Dry chemical agents

Dry chemical agents currently used are a mixture of powders, primarily sodium bicarbonate (ordinary), potassium bicarbonate (Purple K), monoammmonium phosphate (multipurpose). When applied to a fire they cause extinguishment by smothering the fire process. They will not provide securement of a flammable liquid spill or pool fire and it can re-flash after it is initially suppressed if an ignition source is present (i.e., a hot surface). Dry chemical is still very effective for extinguishment of three dimensional flammable liquid or gas fires. It is nonconductive and therefore can be used on live electrical equipment. 

Exposure protection systems provide protection by the application of water to structures and equipment for the anticipated duration of the exposure fire. Water spray curtains are generally less effective than direct application due to unfavorable conditions such as wind, thermal updrafts, and inadequate drainage. Extinguishing agents such as CO2 or dry chemical agents are not able to provide this type of cooling. 

Potassium bicarbonate (Purple K) dry chemical agent in cartridge-type or pressurized extinguishers is compatible with foam. Sodium bicarbonate agent may be used where potassium bicarbonate is not available or approved for general... 

Acids such as sulfuric, hydrochloric, nitric, phosphoric, perchloric, formic, acetic, chlorosulfonic, 50% hydrofluoric, and adipic can be treated by a mix of magnesium oxide and other chemical additives. It must be expected that when the dry chemical agent is applied to an acid spill, there will be a momentary increase in the volume of vapor coming off the spill. This puff is caused by the heat generated from the neutralization of the acid. To protect the personnel applying the dry chemical cover from this puff, suitable personnel protective equipment should be worn. 

Such treatment results in a residue that is salt-based, e.g., magnesium sulfate from sulfuric acid. Thus, dry chemical agents should be readily available in areas where such materials are stored and handled, for example, tank track transfer sites. The application systems or equipment for application of dry chemical agents should have their locations marked. These areas should be kept clear, marked, and inspected periodically in the same manner as fire extinguishers. 

Dry chemical agents are nontoxic, but personnel in the area when they are being discharged may experience respiratory difficulties and vision problems due to the copious amounts of powder in the air. 

Dry chemical agents reduce visibility when they are discharged, they pose a breathing hazard to humans, clog ventilation filters, and the residue... 

Dry chemical agents are effective on flammable liquids, greases and other class B fires. They are also effective on small fires in electrical equipment such as panel boards, switchboards, and other class C fires. 

Dry chemical agents do not work well on deep-seated fires in ordinary combustible materials such as wood, paper textiles, and other class A fires. This is especially true where the cooling effect of water is needed for complete extinguishing of the fire. 

Most dry chemical systems use sodium bicarbonate. This dry chemical agent works best to extinguish flammable liquids, but also works on electrical fires. One problem with this agent is that it is corrosive and can damage the finely polished metal surfaces found in electrical equipment. 

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