A chemical plant for the production of fertilizer was built in 1969 and located over 7 miles from the town of Jonova which had a population of 40,000. The plant employed 5,000 people and was positioned inside a military zone with controlled access. The ammonia tank involved in the accident was a cryogenic storage vessel with a capacity of 10,000 tons (t) (inside diameter was 30m with a height of 20m), of Japanese design but built by the Soviets in 1978. The reservoir had a single wall insulated with perlite held in place by an external skin of steel. The gap between this skin and the reservoir wall was filled with nitrogen under low pressure. This tank, designed to resist an internal pressure of 1.5 psi, stored liquid ammonia (density: 0.68) under slight overpressure (1.2 psi) at a temperature between -26°F and -29°F.