Overview
During start-up operation of a high-temperature, high-pressure plant using hydrogen, hydrogen gas leaked from the flange of a heat exchanger and a fire occurred. The leakage occurred for two reasons:

Insufficient tightening torque control was carried out during hot-bolting and an unbalanced force was generated across the bolts.
A temperature rise was induced across the heat exchanger as a result of a revamping activity, during a turnaround shutdown.

Background
Hot-bolting: In equipment and piping that operate at high temperatures, as the temperatures rise, the tightening force decreases, thus re-tightening of bolts is necessary. This work is called hot-bolting. The design conditions of the evaporator where the fire occurred were 2.4 MPaG, view more

Incident SynopsisDuring shipping preparation operations, out-gassed hydrogen/oxygen from a recently discharged silver/zinc battery in a hermetically sealed drum was ignited. Ignition was caused by a spark generated by the scraping of the battery against the side of the drum. An explosion occurred, blowing the lid from the drum, charring desiccant bags within the drum, and causing other damage.CauseThe cause of the incident was inadequate handling/transporting/storage techniques. The battery was placed in the drum too soon after discharge.