Abstract: At 6:15 a.m. on October 26, 2021, two employees were starting-up an asphalt plant for the morning shift. While conducting start-up procedures and inspections, the employees discovered the ignitors to the west-side liquid propane gas (LP-Gas) vaporizers were not staying lit and began troubleshooting. The vaporizers are fed LP-Gas through steel piping connected to a storage tank 100 feet away, with pilot flames used to ignite the vaporizers that heat the dryer drum and liquid asphalt storage tanks. The employees locked out the electrical breaker switch for the affected vaporizer unit and turned the in-line valve to the closed position to block LP-Gas flow. The employees did not turn off the east-side LP-Gas vaporizer's pilot flame. Employee #1 opened the drip leg valve on the side of the vaporizer cabinet and burner pressure tap to relieve pressure and drain remaining LP-Gas. The employees decided to replace the existing magnetic plunger valve. Employee #2 went to retrieve a new plunger valve, while Employee #1 removed three of the valve's four bolts but had difficulty with the last bolt. Employee #2 had returned when Employee #1 removed the last of the four bolts which loosened the plunger valve, opened the valve and caused the release of LP-Gas trapped between in-line and plunger valves. Since the residual LP-Gas was under pressure, the released gas traveled quickly towards the east-side vaporizer cabinet. Because the east-side vaporizer pilot flame was lit, the gas ignited and exploded into a large fireball. Both employees caught on fire but were able to escape and roll on the ground to extinguish themselves. Two coworkers standing outside immediately responded to provide assistance by grabbing water and a fire extinguisher to put out the fire on the employees and surrounding equipment. First responders arrived and transported the employees to the hospital. Employee #1 and #2 sustained first, second and third degree burns and were admitted to the hospital.