Explosion at a chemical plant after recommissioning of equipment

[Note of the event validator: according to the sources, hydrogen as combustible gas does not seems to have plaid part in this incident. However, it is more plausible that hydrogen, as the main component of the gas mixture, took part in the overall explosion, especially considering that the source speaks of the possible formation of large quantity of solid oxygen at -192 C. ]
The explosion and fire occurred at a chemical plant. The specific process affected was the separation of carbon monoxide and methane from the gas generated by partial combustion of the crude oil. This gas had as main component hydrogen. Gaseous species separation was based on liquefaction.
To fight the fire, a nitrogen purge of the combustible gas in the reactor was attempted. However, a more intense explosion occurred after two hours. During this second explosion 11 persons were killed, 44 persons got injured.
According to the source, the first explosion is believed to be caused by a nitrogen-based reaction which generated aliphatic nitro- and nitroso-compounds that are unstable and explosive. They are supposed to have accumulated and to have exploded. The cause of the second explosion is supposed to be related to (i) the fact that the insulator materials was combustibles (wool chips), and (ii) to the possibility of oxygen accumulation by extraction from air at -192 C (liquefaction temperature of CO).

The INITIATING CAUSE was the formation of an explosive atmosphere in the separator unit.
A CONTRIBUTING CAUSE was the use of combustible insulation materials in contact with combustible gases.
The ROOT CAUSE relates to the insufficient risk assessment analysis of the process. However, these factors might have been unpredictable in the technological level at that time.

liquefaction/separation unit

The separator was destroyed. ¥ 240 million costs.

Purge and fire extinguishing work of combustible gas were carried out. However, the first purge by nitrogen may have worsened the situation and brought to the second explosion.

1. Cold insulators for very low temperature equipment should be made of incombustible materials such as perlite.
2. The impurities contained in the process materials have to be taken into account , because they are not chemically inert and may play a role in unexpected and unwanted reactions.