Abstract: An explosive release clamp adapted to be opened suddenly by electrical initiation of an explosive charge, and a safety pressure release system for closed vessels such as chemical reactors, high pressure storage tanks, or the like, wherein one or more such clamps are used to secure a main hatch to a reactor vessel. Upon occurrence of an emergency condition such as over-pressure, all clamps are automatically fired simultaneously to release the hatch. A manual override circuit enables firing the clamps in case the hatch must be released without an emergency signal. A test circuit checks the clamps and their associated cabling for electrical continuity, using a current substantially less than that required to fire the clamps.