Hydrogen release from a reactor of a pharmaceutical plant

A hydrogen safety detector located above the hydrogenation reactor tripped in a pharmaceutical plant. The internal emergency plan was activated and the personnel evacuated. The operator did not notice any anomaly, except for the faulty hydrogen sensor. Two hours later, the emergency plan was partially cleared. The hydrogenation plant was shut down for the weekend. The 2 sensors were checked.

The post-incident investigation found that the event was due to a hydrogen leak at the level of the spindle seal of the hydrogen supply valve of the hydrogenation reactor located at 3 different places.
This leak had not been detected during the pressure tests, because these tests were not fit-for-purpose.

The INITIATING CAUSE was a leak on the seal of the hydrogen supply valve. The reason n for the leak was not disclosed.
This leak was not noticed in first instance, because the operator noted only the tripping of the detector. Moreover, the leak was probably already existing during the previous pressure tests, but had not been detected.

The ROOT CAUSE was the failure of the procedure aiming at testing the detection systems: this procedure was not fit-for-purpose: the hydrogen valve was closed, the detectors were far from the hydrogen bottles rack, they were activating only on double detection and not on a single sensor, and the sensors wiring was not properly done.
This can be attributed to Job and management factors

spindle seal, H2 supply valve, H2 safety sensors,
hydrogenation reactor

The operator initially failed in understanding the emergency, because reacted on sensor tripping, not recognising the existence of a leak.
Nevertheless, the internal emergency plan was activated and the personnel evacuated. Two hours later, the emergency plan was partially cleared.
The hydrogenation plant was shut down for the weekend.

The internal emergency plan was activated and the personnel evacuated.

Following the event, the operator set up the following actions:
(1) a test of the plant operation ;
(2) a procedure to check the tightness of the whole hydrogen injection line before each hydrogenation and before each batch;
(3) a check of the grounding and electrical continuity of the hydrogenation unit;
(4) an adaptation of the technical equipment;
(5) installation of a nitrogen cylinder to test the installation at the beginning of the campaign and after the change of a hydrogen bottles rack;
(6) automation of the procedures for new leakage tests.