The vessel affected by the incident was a gas storage used for the desulfurisation process. The desulfurization gas had high hydrogen content. The vessels had cracks in the upper transverse fillet welds at the gas inlet which caused low stress brittle fractures. The cracks had been found during the maintenance, but not fixed. This eventually caused a gas release. Approximately 2.5 hours after that a leak was detected and reported, a first explosion occurred. As the heat exchanger explosion was facing the desulfurisation pump room, the leaking desulfurisation gas gathered in the pump room, under the effect of the first explosion flame. 7 seconds later, a secondary explosion occurred in the desulfurisation pump room, resulting in 3 deaths. Due to the impact of debris from the first explosion and the high temperature of the open flame, a third explosion occurred in another cracked pressure pipe.