NIOSH recently investigated ignition incidents resulting fro drilling holes into sealed and filled plow frame sections. A farmer and farm worker were seriously burned in two separate incidents that occurred in the same county in New York under similar conditions. They had just penetrated sealed sections of their plow frames with electric drills when a roar of escaping gas at high pressure was hear, and the victims were thrown back by the gas jet and engulfed in flames. The flames were quickly extinguished, but the victims suffered burns. NIOSH experts were asked to help find the cause of these hazardous incidents. Inspection of the frame sections involved in the incidents showed no discoloration, charring , or blistering of pain in the immediate vicinity of the holes. Probing the holes with a magnetized blade revealed a hard interior fill material and the presence of some metal punching. This fill material was more extensively sampled form another section that had been cut through. The revealed a wide range of metal punching that was used as ballast in these steel frames sections, which had been welded shut after the filling operation. The punching were found to consist of various forms of steel and other metals, including titanium. Stealing the holes and sampling the gases present revealed the depletion of oxygen from the original air atmosphere and the presence of hydrogen. The hydrogen concentration was found to increase with time under sealed conditions. The pressure in the resealed sections also increased with time at a steady rate.