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.
According to the local authorities, part of the liquid ammonia was propelled, in the form of a jet, towards the phosphonitrate production buildings. A fire then spread to the fertilizer depots. Other sources claim that the ammonia cloud was ignited by the flare stack, the flames being then propagated to all the buildings on the site. The collapse of a burning conveyor belt onto a store of NPK fertilizer (11-11-11) would then have initiated the decomposition of the fertilizer which continued for 3 days while releasing large quantities of nitrous oxide (NOx) to the atmosphere.
The emergency services arrived 30 minutes after the accident, the means deployed increased progressively: civil defense, the emergency commission of the Lithuanian Republic and the military region, civil defense teams from the USSR and from the Soviet ministry of fertilizers.
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.
The municipal authorities alerted 25 minutes after the beginning of the accident, decided to evacuate the high-risk areas as soon as the concentration of ammonia in the air exceeded 10 mg/m3 (14 ppm); 32 000 people were thus displaced.
A toxic cloud composed of ammonia vapor and products of the thermal decomposition of the fertilizer (nitrous oxides, ammonia…) was at the origin of irritation observed as far away as 35 km (22 miles) from the accident site.
The contaminated zone extended to 400 km² (154 sq miles).
The estimated height of the cloud at 5, 10 and 20 km (3, 6, 12 miles) from the site appears to have reached respectively 100, 400 et 800 m (328, 1,312, 2,625 feet).
According to the report from the Soviet authorities, the concentration of ammonia along the track of the cloud and within a radius of 3 km (1.9 miles) did not exceed 200 mg/m3 (288 ppm).
The levels found at a distance of 10 to 15 km (6-9 miles) were between 20 and 40 mg/m3 (29-58 ppm)
These relatively low levels of ammonia could be explained, at least in part, by the ignition of the ammonia vapor in the plant. The maximum distance over which the presence of ammonia could be detected in the air was 23 km (14 miles). The concentration of nitrous oxides (NOx) which could have reached 25 mg/m3
on the site close to the storage zone for the phosphonitrates, did not exceed 2 mg/m3 in the wake of the cloud that had formed.
To reduce the impact of the cloud on the surrounding areas, water curtains were set up using fire hoses all along the track of the gas cloud. Furthermore, special measures for the protection of watercourses were taken to avoid the risk of pollution of the nearby NERIS river. Pumping of the extinction water, positioning of containment basins…
CLICK HERE (pdf) for the full report from The Ministry in charge of the environment – DPPR / SEI / BARPI