ABSTRACT Coast Guard Research and Development Center tests of two explosion suppression systems conducted in the forward pump room (18,000 cu ft) of the T/V RHODE ISLAND are described. The experimental suppression systems were specifically designed for the space and fabricated from existing hardware and detection equipment. They are the first systems to effectively extinguish propane-air explosions in volumes as large as 18,000 cu ft. The effectiveness of water, Halon 2402, Halon 1211, Halon 1301, and Purple K g.ry chemical powder as suppressing agents was evaluated. The systems were being evaluated to determine their applicability in pump rooms and other high hazard spaces on tank vessels. They could also be used in of shore-well drilling operations in spaces where gas buildup might occur, such as wellheads, storage tanks, and production platforms. The testing demonstrated that technically it is feasible to suppress explosions generated by rapid oxidation of vapor/air mixtures in large volumes. For the various extinguishing agents, the tests indicated that successful suppression requires twice as water as Halon and approximately 10 times as much Halon as dry chemical (Purple K) by volume. The results of the work will be used as a basis in establishing criteria for evaluating explosion suppression systems that may be submitted to the Coast Guard for approval. INTRODUCTION This program was conducted by the U. S. Coast Guard in a cooperative effort with Fenwal, Inc., and Detector Electronics Corp. The contributions by these firms and their personnel in providing material, equipment, and expertise led to the successful accomplishment of the program. The results of the test program will be used by the Coast Guard's Office of Merchant Marine Safety in the development of standards relative to the acceptance and approval of explosion suppression systems proposed for installation on board U. S. merchant vessels. Explosions on vessels of all types are inherently difficult to control. One of .the areas aboard tank vessels which has been prone to explosions has been the pump room. This area is the heart of the cargo transfer system. Cargo, pump, valves, piping systems, and attendant leakage are concentrated in a tanker's pump room. The energy necessary for cargo transfer coupled with the multitude of flanges and. fittings make these spaces prime candidates for conditions conducive to explosions and/or fire. Fire protection systems presently required. for the protection of these spaces were not designed to mitigate the effects of a potential explosion. In spite of improved operational -techniques, there have been 1,000 tanker fires/explosions worldwide since 1950.1,2 A typical scenario that has occurred follows. The vessel is offloading cargo of high octane gaseline into a shoreside pipeline. Approximately 4 minutes prior to the completion of the offloading, a small leak develops in the flanges between the cargo pump and the discharge piping. The gaseline, a low flash point liquid, has space. The cargo pump runs dry and immediately begins to overheat. Within minutes the stoichiometric mixture surrounding the cargo pump is ignited, setting off an separating the pump room from the adjacent machinery space buckles and is breached.