A leak of 4 t of ethylene oxide occurred in a chemical facility at around 10:40 p.m. The equipment involved concerned two check valves and a valve downstream from a pump while they were being put back into service. The leak occurred when the operators opened the valve after having primed the pump. The product, at a pressure of 67 bar, sprayed onto the operator, who was able to rinse himself off with the safety shower. However, he suffered chemical burns as he had not removed all his clothing.

The leak was caused by the rupture of the check valve’s seal due to a detonation in the valve head.

This explosion was caused by:

• the simultaneous presence of air and ethylene oxide vapour
• overheating produced by the compression of vapours by the pressure wave front, created when the valve was opened.

A safety valve should typically prevent the propagation of a pressure wave through the liquid, but this valve was not closed since it was stuck due to an accumulation of polymerised products. Furthermore, the presence of impurities in the system may have contributed to the detonation by lowering the self-ignition temperature of the ethylene oxide from 450 °C to 150 °C.

Following the accident, the operator planned to:

• study and modify its installation to prevent the accumulation of vapours at a high point that is inaccessible to the purge,
• modify its procedures for the restart of the facilities, by integrating liquid filling, purging or inerting of the pipes,
• identify the equipment under pressure and set up procedures for the use and maintenance of such equipment,
• renew employee training on the procedures to follow in the event of an accident, notably insisting on fully undressing when the safety shower is used,
• place a change of clothing near safety showers to encourage operators to fully undress during rinsing.