Explosion at a hydrogen compressor of a sand oil company

The explosion occurred at a sand oil an explosion and affected the hydrogen compressor and its building, serving the hydrocracker unit.

(1) More than two months before the incident, a large hydrogen release had already occurred due to the fail of the seal of the recycle compressor. This was the consequence of a series of events which had started with the trip of the pressure-swing absorption unit, causing the make-up compressor to shut down. When it was restarted, the recycle compressor seal system failed. Approximately 1500 kilograms of hydrogen were released into the building, which apparently did not ignited and did not cause any modification of the maintenance routine.

(2) Ten days before the incident, the compressor to be overhauled was isolated from the rest of the facility, and the works to replace eight valves started. According to the investigation report, from days to days the maintenance team have been busy with various actions, up to the dismantling of some of the valves. During these days, the team compositions had changed, and unexperienced workers had joined. Also, the supervisors had been replaced by a less experienced one.

(3) The explosion occurred on the day when all the valves were dismantled. According to one of the sources, the workers were not familiar with the site procedures, and the error triggering or enabling the incident was due to having isolated a single stage of a compressor rather than both stages .

The INITIATING/direct cause was the release of large quantity of hydrogen from the compressor being maintained, occurred when dismantling a valve. During the starting days of the maintenance, high temperature had been recorded on the compressor valves, the pressure-swing absorption unit has triggered, and the restart of the make-up compressor had caused a loss of integrity at the recycle compressor.
The court charges to the company related to the failing to ensure the health and safety of the workers, and failing to ensure the compressor equipment was serviced in accordance with manufacturer's specifications. From this, it can be deduced that the root cause were due to Management shortcomings and Job Factors contribution.
(i) The former is due to the lack of proper risk assessment, which did not consider the possibility of a large release of hydrogen, even if this had already occurred at the first day of the maintenance. It appears that the company was not (completely) understanding the complex phenomena occurring in the facility.
(ii) The latter can be deduced by the fact that the workers had been asked to volunteer on the week end, and that the usual morning brief before starting works was not executed for a last days before the incident.

suction and discharge valves, hydrogen compressor

DESCRIPTION OF THE FACILITY
The compressor building included two make up gas (two stage) compressors and a recycle gas compressor (centrifugal steam driven turbine), plus ancillary equipment such as fixed gas detectors and piping and flanges etc. Hydrogen was fed into the unit from the pressure swing absorption unit. Once the hydrogen was compressed, it was combined with gas from the recycling compressor to produce reactor feed gas at 19.3 MPa.

Two fatalities. Extensive damage to the compressor. The authority enforced a stop of the activity before court's decision. The company probably never reopened again the unit.

The court asked sanction up to 500000 Canadian $ and possible a jail sentence.

From outside the building, the explosion was felt and heard as a large bang. Smoke was coming from the same area as where the hydrogen compressor building was located. The company emergency response team, as well as the company fire department, responded to the scene and began extinguishing the fire while searching for the missing personnel.

The Investigation report does not provide lesson learnt and recommendations. It is clear from it, nevertheless, that

(1) Risk assessment should have been reviewed following the first, unignited release, which was clearly demonstrating the possibility of such an event;
(2) The maintenance team should have worked with knowledge and expertise which was lacking among their members;
(3) The team should not have improvise the actions steps according to the finding of the overhauls;
(4) The workers should not have been asked to volunteer to work on the weekend (possibly due to time pressure);
(5) The missing workers, who did not volunteered, should have never been replaced with unexperienced one.