An employee was opening an oven door in the paint department to expedite cooling. The employee entered the door to Stage 1 and 2 and the vacuum system in the oven sealed the door making it difficult to open. The employee was burned on the hand when he tried to exit the oven. The oven reached a temperature between 300 to 400 degrees Fahrenheit when in operation. It had been turned off for approximately one and a half to two hours at the time of the incident.