Abstract: At 10:38 a.m. on July 27, 1994, Employee #1, of Montenay Pacific Power Corp., a municipal trash incineration facility, was attempting to determine if the ash extractor for boiler #1 had excessive ash buildup. This was normally done by sliding the cover plate on one of the drag conveyors down and looking through the drag conveyor's discharge port into the area above the ash extractor. He had asked that the drag conveyor be bumped so that the conveyor's discharge port could be cleared of any ash overlay. At the same time, the furnace for boiler #1 went positive. When this occurs, air no longer flows from the outside into the furnace. Instead, furnace gases and ash flow through any available opening out into the surrounding environment. Employee #1 was scalded or burned when steam and debris spewed from openings in the ram and south drag conveyor. He was transported to St. Mary Medical Center in Long Beach and was then transferred to the burn ward at Torrance Memorial Medical Center. He suffered second-degree burns to 30 to 35 percent of his body including his hands, arms, face, back, neck, and bilateral extremities. Employee #1 had been wearing heavy cotton long sleeve overalls, a hard hat, safety glasses with side shields, and leather gloves. The exact cause for this particular excursion into the positive pressure range is unknown. It is not unusual, although no one interviewed recalled an excursion of this apparent magnitude. The board operator reports, based on no recording of the event on the distributive control system, that the excursion lasted less than 60 seconds. Past excursions have been attributed to trash having rapid burning capacity, such as a partially filled propane bottle exploding, or trash which can release large volumes of inert gas or steam, such as an explosion of a partially filled water heater. Either event simply pushes the furnace gases and debris out of the furnace. The port holes upstairs in the furnace grate area have deflecting plates between the viewer and the furnace, but no such arrangement exists on the ground floor for ash extractor area.