While on site a contractor entered the electrical storeroom for maintenance and closed the door behind him. When the contractor tried to exit the room the handle wouldn't open the latch. There was no second exit in the room, and the contractor didn't have his cell phone on him as he had been working in the hazardous area. After an hour of trying, the contractor was able to escape the room by disassembling the door handle with the limited tools he had on him.