Abstract: Employee #1 was preparing stock for inventory on the second floor of a parts storage area. As he was arranging floor mats he heard a hissing noise and proceeded approximately 15 ft to the end of the aisleway. As he reached the end, an explosion occurred, knocking him into the storage bins. He got up and started running away from the immediate area before losing consciousness. Coworkers removed him from the area and first aid was provided by an on-site EMT. The 911 system was activated and the Maryland State Police helicopter transported him to Baltimore Shock Trauma Center. Investigation revealed that the motor bracket of a 5 ton air conditioning unit had failed, resulting in the motor falling into the cooling fan. Head pressure built up in the air-conditioning lines on the second floor. As the pressure approached 440 psi, the elbow in the line failed, sending freon gas into the employee's work area.