Fatality: overpressure of an explosion-proof enclosure

What happened?

International Association of Oil & Gas Producers (IOGP) has published an alert regarding an incident in which an engineer was fatally injured.  He was killed when he removed the cover on an explosion-proof enclosure, as part of a routine task.  The threaded cover, measuring 35cm across and weighing around 6kg, was forcefully propelled from the enclosure as the engineer unscrewed it, inflicting fatal head injuries.

What went wrong?  What were the causes?

  • Pressure built up inside the enclosure from leaking sample gas or instrument air components;
  • The enclosure was not equipped with an external indicator to indicate the pressure inside;
  • There was no means to relieve internal pressure in the enclosure.

What lessons were learnt?  What actions were taken?

IOGP identify the following lessons:

  • Recognize the potential hazard of trapped pressure in explosion-proof electrical enclosures from all sources of energy entering the enclosure;
  • Identify explosion-proof enclosures which are susceptible to trapped pressure scenarios and do not have pressure indication or pressure relief protection;
  • Work with equipment manufacturers to develop a mitigation plan that addresses the trapped pressure situation while still maintaining the electrical certification of the identified enclosures.

The incident can be found on the IOGP website.