The Hazmat Employee is a man who works as a hazmat employee at the Springfield Nuclear Power Plant.
He is seen transporting uranium and other assorted nuclear products while in a sealed room, as it is a dangerous procedure. Suddenly, not known by the hazmat employee, Homer, Lenny, Carl and Charlie play a prank on him by pinching him on the behind with a robotic arm. This makes him drop the carbon rod in his hand, releasing a lethal mist. He runs up to the safety glass and bangs on it while pleading for help, but Homer and the others fail to respond. They do nothing, assured that the glass will protect them. The safety glass, however, seeps out the gas and they attempt to escape through an exit. However, the exit is only painted on and they ae consumed by the mist.
It is most likely that the hazmat employee died from the mist, as he seen dropping to the ground. But Homer and his friends all escape from the mist alive, which leaves a possibility that he also did. However, Charlie describes it as a "miraculous escape", implying that there was more to the escape. This means that the hazmat employee probably survived, and dropping to the ground from the mist might have been him losing consciousness.