Abstract: At approximately 7:10 p.m. on July 25, 1991, Employee #1 was working on Alclo, an explosive ignitor substance, for content testing by grinding the pellet form (25 to 40 grams) in a mortar and pestle. After Employee #1 had been grinding the substance for approximately 15 minutes, an explosion occurred that caused second- and third-degree burns to both of his hands and forearms. A piece of the mortar became embedded in his abdominal wall and he sustained minor cuts to his face. He was using safety glasses, but no other engineering controls or personal protective equipment was used. Employee #1 received first aid care from a coworker until the fire department and paramedics arrived. He was later transported to the UC Davis Medical Center by Lifeflight helicopter.