Explosion

An explosion without fire or gas emission occurred in the washer of the catalyst activation unit. The unit was stopped for maintenance : 3 external employees were checking the washer. The explosion occurs just after the opening of the manhole on the washer. The employee looking through the hole at this moment was seriously injured.

One of the possible cause of the explosion could have been to the presence of hydrogen in the washer. Another cause, considered more probable by the ARIA report (see references) could be a secondary reaction or a reaction activation which was still running in the washer.

washer, catalyst activation unit, Production of hexamethylenediamine

DESCRIPTION OF THE PROCESS
The catalyst was produced with a mixture of aluminium and nickel which reacts with soda to produce Raney nickel and hydrogen. Hydrogen is evacuated by the ventilation and the Raney nickel is transferred in the washer.

Prevention plans will be improved. The water seal of the washer is separated from the rest of the unit to avoid hydrogen entry.
Evacuation plan will be improved.

A pedestrian heard the alarm and called the police, who called the station manufacturer. In parallel, the operation team received the alarm at their remote monitor. Police called the fire brigade and installed a safer perimeters of 200 m, closing all the roads.
The station manufacturer technicians were called on-site and arrived 2 hours later. They started a controlled additional de-pressurisation through a vent line bypass which brought the hydrogen to the bus dispenser vent line. After approximately 5 hours, the pressure in the affected hydrogen container was at around 1-2 bar and could be sealed again.

(1) To eliminate the risk of the accidental presence of hydrogen coming from other part of the installation, hydraulic safeguard of the washer was isolated from the other units;
(2) The incident prevention plan of the factory was improved;
(3) The evacuation rules were reviewed and improved.