On 28th August 1992, in a food factory, a liquefied nitrogen storage tank catastrophically failed, causing the destruction of the upper half of the factory as well as damaging other factories and structures partially, including the outer walls, window glass, and shutters of 25 buildings, 39 parked vehicles consisting of busses, trucks and cars, and electric poles in a circle with radius of 1,304’ (400 meter). Fragments of the vessel were projected up to 1,150′ (350 meters), the largest of which, a section of the outer shell head was 5’ (1.5 meters) wide and 8mm thick. The tank was a vertical type, double shell, vacuum insulating vessel (model CE-7500). The piece of the vessel that flew the furthest was the top dish plate of the outer vessel, 1.5m in diameter and 8mm in thickness that reached a distance of 1,148′ (350m). The insulator composed of pearlite scattered over a circular area with a radius of 328′ (100m). The direct cost of the damage was estimated to be about 440 million yen ($443K).
The tank was a double-walled vacuum insulated ultra-low temperature storage vessel designed to operate at —320°F (196°C) and 135 psi (9.3 bars) maximum normal operating pressure. The inner vessel broke into seven fragments and the outer vessel broke into eleven main fragments and numerous smaller pieces. It was discovered during the course of the investigation that most of the valves on the system were closed including the top liquid inlet, liquid outlet and the isolation valves for the relief valve and bursting disc. The vessel was therefore under completely closed conditions at the time of the accident. The bursting disc was found to be ruptured despite the closed inlet valve, however, it was believed that the valve might have been closed after the disc ruptured on a previous occasion. The inner and outer shells ruptured as a result of excessive pressure under closed conditions. It was estimated that the inner shell ruptured at a pressure of 996 psi (68.7 bar). The pressure reached this level as a result of heat inflow over the sixty days between its final filling and the time of the explosion.
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