Brits called in to solve riddle of Mexico gas blast which killed 37

British experts were called in to establish how a gas buildup caused a blast at the state oil headquarters in Mexico City, killing 37 people.

They joined a team of inspectors from Mexico, Spain and the US. The authorities said investigators were still looking for the source of the gas and revising records of building inspections to determine why Petroleos Mexicanos had not discovered the gas accumulation.

The blast appears to have happened after the buildup was ignited by an electrical spark or other heat source.

The investigators found no evidence of explosives in the blast that collapsed several lower floors of the Pemex administrative building.