Release of chemical substances (including hydrogen) from a chemicals production plant

The event was initiated by the burst of a rupture disc on a reactor during a hydrogenation process. The hydrogenation reaction occurs under pressure in a tank containing 3,000 l of a mixture of ethanol (a flammable and toxic solvent), red hair dye, a catalyst (palladium on carbon) and hydrogen.
As a result of the disc rupture and the following tank decompression, part of the tank content was expelled and landed on the roof of the building.

The emergency action consisted in stopping the supply of hydrogen and to purge the tank with nitrogen.

The internal investigation showed that the disc’s maximum operating pressure was 2.83 bar, rather than assumed 3.7 bar. The hydrogenation process operates at pressures up to 2.9 bar.

Following a reference change, the rupture disc supplier did not validate the characteristics of the new model sold to the operator, who had not been informed of the reference change.

A possible additional contribution to the event could have been the 10-year inspection of the seal and the graphite performed a month earlier, which may have weakened the disc.

The INITIATING cause was the premature burst of the rupture disc under nominal working pressure condition.

The root cause was the delivery by the contractor of a disc with different characteristics, without informing the plant operator.

A contributing cause could be the absence of an independent control of components by the operator.

burst disc

A maintenance intervention performed one month before the event may have damaged or weakened the disc.

411 kg ethanol et 23 kg of reaction products are dispersed mainly to the ground, part of the ethanol is dispersed in the atmosphere.

The emergency state of the plant is called few minutes from the burst. The system is made safe by stopping the hydrogen supply and filling the reactor with nitrogen.
The valves of the rain water network are closed to confine the water contaminated by the liquids released. This waste is burned in the evaporator of the plant. The emergency is called off half hour after the event.

Despite the corrective measures implemented, it remains unclear how these could guarantee avoiding the recurrence of the same accident, in absence of an internal procedure aiming at regularly checking subcontractors deliveries.

According to the ARIA report (see references), following the accident, the operator reviewed the reactor qualification documents, including the max. operative pressure of the rupture discs. All the discs in place on other reactors were checked and the discs below specifications were replaced.
The maintenance personnel were made aware of the importance of the proper assembly of rupture discs on the reactors.