Abstract: ON AUGUST 7, 1987, EMPLOYEE #1 WAS TESTING A TDM SERIES, MODEL 200, INDIRECT FIRED SPACE HEATER. THE UNIT WAS CONNECTED FOR TESTING AND THE MAIN GAS VALVE HAD BEEN ON FOR TEN MINUTES. THE FLAME DROPPED OUT AND THE PILOT LIGHT STAYED LIT. HE OPENED THE PUFF DOOR ON THE HEAT CHAMBER. THE UNIT OPERATES ON .2 INCH NEGATIVE PRESSURE. THE GAS VALVE CONTINUED TO FEED NATURAL GAS INTO THE BURN CHAMBER. THE ADDITIONAL AIR THAT WAS ADDED WHEN THE PUFF DOOR OPENED CAUSED A RAPID BURN OR EXPLOSION. THE EMPLOYEE SUFFERED 2ND DEGREE BURNS OVER 40% OF HIS BODY. EMPLOYEE #1 WAS WEARING A POLYESTER T-SHIRT THAT COTRIBUTED TO THE SEVERITY OF THE BURNS. THE FLAME WAS SET ON IN THE HIGH FIRE POSITION. AN OUTSIDE FIRM WORKING FOR THE INSURANCE COMPANY FOUND NO PROBLEMS WITH THE EQUIPMENT. SAFETY GLASSES WERE WORN AND PREVENTED SERIOUS EYE INJURY.