Abstract: On April 18, 2009, Employee #1, a diesel truck mechanic, was welding an aluminum diesel tank to repair the top base that had a perforation or crack. Employee #1 welded about a 2.5 in. line when an explosion occurred. He was thrown back due to the explosion and clothing set on fire to his right side upper torso area. Employee #1 stated that the gas cap was not removed or unscrewed, because he thought it was purged of compressed gasses. He was not trained on welding diesel tanks and the gas cap was not removed or unscrewed to ventilate the residual diesel. Employee #1 was transported to Centinela Hospital Medical Center via ambulance, where he was treated and received skin graft surgery on his right side upper torso area. He was hospitalized during the surgical procedures. From the investigation, it was found that the employer did not submit training documents, indicating that Employee #1 had been trained in general safety, or was trained on how to safely weld on diesel tanks. The casual factor that led to the incident was that the gas cap was not removed or unscrewed and compressed diesel gases within the tank ignited and caused the explosion. Furthermore, Employee #1 was unaware of this hazard due to lack of training by the employer.