DCA86IA037

A charter flt arrived & deplaned without incident & with no indication of smoke, fumes or heat. Company maint psnl had placed damaged passenger seatbacks (incorporating solid-state chemical oxygen generators) in the fwd cargo compartment with seat covers & oil. A company mechanic examined the seatbacks to find a serviceable unit. He found a loose oxygen canister & handled it improperly by its oxygen hose. Such handling can release the firing pin, fire the percussion cap, trigger a chemical reaction, & generate oxygen. This can generate up to 430 deg of heat outside the canister. A fire bgnin the fwd cargo compartment in the vicinity of where an oxygen canister was fnd (later) with a dented striker plate. The seat covers ignited, fire burned thru the cabin floor, & subsequently, it spread throughout the entire cabin. Company maint psnl did not know that oxygen generators, carried as company supplies, were hazardous materials. The mechanic was not familiar with the repair or installation of the passenger supplemental oxygen equipment.