Abstract: An employee working for a heating and ventilation contractor sprayed a coating of a flammable adhesive containing methylene chloride to the inner surface of a sheet metal duct section. The employee then positioned a piece of precut fiberglass insulation against the glued surface and allowed it to set for approximately 5 minutes. He then spot welded retention pins through the fiberglass insulation and onto the sheet metal using pinspot-type welded insulation fasteners. The electric arc generated by the spot welder ignited the flammable vapors from the adhesive, which were trapped in the air spaces in the insulation. The ensuing flash fire burned the employee's face, neck, right ear, and inner right forearm. He was hospitalized for 5 days. (The spray application of the flammable adhesive and the spot welding were conducted in a general shop area, not a well ventilated work station.)