Abstract: Employee #1 was cleaning ash out of the abort duct that came off a hull burning operation. The abort duct has a 38 in. square opening above a round duct (2 ft 4 1/4 in. radius) and is 5 ft 1 1/4 in. from top to bottom. With the duct lid open, Employee #1 stood on a ladder next to the duct opening and used long-handled tools to remove the ash. There was a continuous release of smoke and ash from the smoldering rice hulls in the burner. It is believed that Employee #1 was overcome by carbon monoxide and fell off the ladder into the abort duct. He was killed. Employee #1 was working alone during the operation shut-down. He wore a half-face respirator with organic filters and dustpads