Abstract: At 3:00 p.m. on September 18, 1992, Employee #1 was using an aluminum extension ladder to descend 12' 9" from a roof line to the grating on which the ladder rested. Employee #1 was on the third or fourth rung when the grating gave way and he fell approximately 29 to 30 ft into an air shaft that was 20 1/2 ft deep by 15 ft long by 4 ft wide. He suffered severe head injuries, which required brain surgery and hospitalization, and remains in an induced coma. The air shaft was covered by standard grating supported by an angle iron that was anchored with two red head bolts that appeared to be approximately 1/2 in. in diameter. The bolts sheared off, causing the angle iron grating and the ladder, which was not secured at the top, to fall into the shaft. Prior to being placed at the location from which it fell, the ladder had been used near the center of the roof and extended through an area not yet decked; the ladder was tied off at that location. When the steel crew needed to complete the decking, the ladder was moved to the northwest corner and placed on the grating with its top wedged against the roof edge which met with a wall that extended from the roof at a 90 degree angle. Causal factors include the ladder being placed on an unstable surface and not being tied off at the top. The investigation revealed that employees of the general contractor, employees of the drywall crew, and the steel workers had all used the ladder while it was in that position.