A plant operator heard the escaping propylene and the expanding vapor cloud. He notified the plant's control room of the problem. The control room operators saw the leak on a closed circuit television and began to shut down the plant. However, valves that would have prevented further release of chemicals had to be shut off manually. Operators in the vicinity of the leak attempted to reach manual shutoff valves but were driven back by the vapor cloud. As a result, the explosions continued and the fires grew. Fire monitors were turned on.