Abstract: At 9:00 a.m. on May 26, 2020, an employee working as an automotive technician for an autobody shop was attempting to vent compressed natural gas tanks situated on top of a city bus. The employee was preparing to replace potentially defective pressure relief devices (PRD) as a part of a recall retrofit. The employee did not ground the bus at its grounding point. The employee also did not defuel the bus utilizing the defueling instructions on the bus. The employee attempted to heat up the PRDs using a heat gun to a temperature that would cause the PRDs to activate and vent the tanks. While performing this task, a sudden flash fire occurred, burning the employee and destroying the bus, as well as the two busses parked next to it. The most likely contributing factors to this accident were, lack of proper grounding, lack of proper procedures for defueling the bus, and hazardous method employed to pop off potentially defective PRDs to vent the tanks quickly. The employee sustained 2nd and 3rd degree burns to his arms and hands and was hospitalized.