Abstract: ON DECEMBER 31, 1985, 5 EMPLOYEES OF SHELTER SYSTEMS CORP OF MD. WERE SERIOUSLY INJURED WHEN WOODEN ROOF TRUSSES, 72' LONG, WEIGHTING 200 TO 300 POUNDS APIECE, TOPPLED AND COLLAPSED 20 FEET TO THE GROUND. 3 OF THE 5 EMPLOYEES WERE TREATED AT THE HOSPITAL FOR SPRAINS, STRAINS AND ABRASIONS AND RELEASED. 2 WERE ADMITTED FOR SURGERY. 1 HAD A COMPLETELY CRUSHED RIGHT HEEL, THE OTHER CRUSHED VERTEBRAE. THERE WAS ONE MORE EMPLOYEE WHO ESCAPED ALL INJURY. DURING THE INVESTIGATION IT WAS FOUND THAT SHELTER SYSTEMS CORP OF MD., A MANUFACTURER OF WOOD FLOOR / ROOF TRUSSES, WAS IN THE PROCESS OF HAVING AN ADDITIONAL BUILDING (72'W X 116'L X 20'H) CONSTRUCTED AT ITS FACILITY. THEY HIRED AN INDEPENDENT CONTRACTOR TO SUPERVISE/COORDINATE CONSTRUCTION ACTIVITIES. THE WOOD ROOF TRUSSES WERE MANUFACTURED ON SITE. WHEN THE TIME CAME TO ERECT THEM VOLUNTEERS WITH LITTLE OR NO EXPERIENCE ERECTING WOOD ROOF TRUSSES WERE GATHERED TO WORK UNDER THE INDEPENDENT CONTRACTOR. THESE EMPLOYEES ERECTED 14 OF THE TRUSSES THE DAY PRIOR TO THE ACCIDENT AND 13 ON THE DAY OF THE ACCIDENT. THEY STOPPED ERECTING THE TRUSSES BECAUSE OF PROBLEMS ENCOUNTERED WITH THE TRUSSES SET THE PREVIOUS DAY. APPARENTLY, INSUFFICIENT TEMPORARY RIGGING HAD RESULTED IN THE TRUSSES NOT BEING PLUMB. THE EMPLOYEES SPENT A CONSIDERABLE AMOUNT OF TIME TRYING TO BRACE THE TRUSSES SET THE PREVIOUS DAY. 4 EMPLOYEES WERE WORKING ON THE TRUSSES, A FIFTH WAS BRINGING 2 X 4'S UP FROM GROUND LEVEL, USING AN UNSECURED PORTABLE LADDER. MEANWHILE, THE SIXTH EMPLOYEE AND A SINGLE EMPLOYEE OF THE INDEPENDENT CONTRACTOR WERE ADJUSTING THE SPACING ON THE TRUSSES SET THE DAY BEFORE. A LOUD CRACKING NOISE WAS HEARD AS THE 13 TRUSSES TOPPLED AND COLLAPSED TO THE GROUND.