The explosion that killed three workers on a Gulf of Mexico production platform in November 2012 was caused by contractors who were doing maintenance work at the site, according to a third-party investigative report commissioned by the Houston-based oil platform operator Black Elk Energy Offshore Operations.

While federal investigators are still looking into the cause of the explosion and fire at Black Elk Energy production platform, a report by ABSG Consulting concluded that contractors, Grand Isle Shipyard (GIS), were welding a pipe that still contained some flammable gas inside, triggering the explosion in connected oil tanks.

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The report stated that GIS had allowed inadequately trained subcontractor employees to carry out the welding operations. While the contractor did not comment on the latest findings, its CEO Mark Pregeant had previously rejected the theory that the fire was started by workers while they were cutting a water line.

Black Elk claimed that GIS had breached the company's safety policies, including the rule that all "hot work" — burning, welding or other operations that can start fire — should be carried out after a supervisor has made sure hazards have been removed. It also accused GIS of allowing a subcontractor, Philippine-based DNR Offshore and Crewing Services, to conduct "sensitive work," despite that fact that this was against the terms of the contract.