On March 20th, 1989, the pressure in the cryo tank climbed abruptly between 11:00 a.m. and 11:15 and the tank burst at its base. Under the effect of the wave escaping from the gaping breach, the reservoir broke free from its stand, pushed in the opposite direction. It destroyed the reinforced concrete protecting wall and ended up 131′ from its foundation. The 7,000 tons of ammonia contained in the tank spread over the ground forming a layer which was, in places 28″ deep. With only a light wind (< 4.5 mph), it took 12 hours to evaporate. The official human casualty list cited 7 deaths and 57 injured (treatment lasting from 2 to 3 weeks) among the operational personnel of the plant and of the construction companies working close to the accident site.