Wall coverings and decorative materials had been approved on the basis of tests for ordinary ignition, which showed resistance to combustion from sources such as matches and cigarettes. Decorative cloth was purportedly treated with ammonium sulfate as a fire retardant upon installation, but there was no documentation that the fire retardant treatment was maintained at the required intervals. Since the US entry into the war, air-conditioning systems had been serviced and the freon refrigerant was replaced by a flammable gas called methyl chloride, due to the wartime shortage of freon.