Explosion in a process reactor of a chemical plant

Explosion in a fine organic chemical plant (Seveso classified )

The event occurred during the cleaning of a reactor. At the completion of a batch manufacturing of a soft reducing agent, an operator was rinsing the 3000-litre reactor first with a solvent and then with a water jet . Noticing a smoke release, they informed their team leader, who opened the manhole of the reactor. This action caused a flash type explosion at the reactor entrance.

According to the ARIA report (see references), the rinsing water reacted with sodium hydride (NaH) residues on the reactor walls to form hydrogen. The hydrogen then mixed with air outside the reactor to form a highly explosive mixture that ignited.

The INITIATING cause of the incident was the mixing water with sodium hydride residues, which formed hydrogen which reacted wit hair when opening the reactor.

The ARIA report does mention that team leader, although experienced, had not followed the procedure for securing the reactor before opening it..

But which was the root cause? Was the rinsing operation performed according to a procedure? Was it a standard operation?

chemical reactor

The incident occurred when cleaning the reactor

Two injured, one severely, the other lightly. No material damage.

The ARIA report (see references) does not mention the corrective actions taken.
Too less is also known on the cleaning process procedure to deduce a lesson learnt.

ARIA report that the team leader was experienced, and nevertheless did not take the required safe measures before opening the reactor. This suggests at least the need for raising the safety awareness.
Possibly, various procedure should be also reviewed, and the risk of hydrogen formation assessed.