Extinguishing Class A fires with multipurpose chemicals

We investigated the extinguishing properties of multipurpose dry chemicals using openregime cribs of two sizes. One measured 20.3 by 20.3 by 15.2 cm, and the other 50.8 by 50.8 by 38 cm. A crib fire, which has both flaming and smoldering contributions, is primarily extinguished when the burning surfaces are covered or smothered by a gas phase of the original multipurpose agent or a product of the agent's decomposition. The overall effectiveness of each dry chemical depends on its particle size, the degree of its decomposition and/or vaporization, and the openness of the crib. All particles of an agent below a unique limiting size completely decompose and/or vaporize in the crib fire and have the same extinguishing effectiveness. Particles above the limit have no measurable effectiveness. Scaling is considered on the basis of the minimum extinction weight per unit of exposed wood surface.