While a mechanic was working on an airplane in the hangar, a spark ignited some raw fuel below the engine and started a fire. The mechanic reacted quickly, using a multipurpose dry chemical fire extinguisher. The fire was quickly put out, but the aircraft and several other aircraft nearby were severely damaged. It wasn’t the fire that caused the damage—it was the extinguisher.
Source: aopaAircraft Maintenance: Choose your fire extinguisher carefully