More gas buildups feared under Pemex’s offices

While the Mexican government has ruled out foul play in the explosion at the headquarters of the national oil company Petróleos Mexicanos (Pemex) that killed 37 people, authorities on Wednesday said they were concerned over more gas buildups in other areas of the offices.

"Right now we cannot smell anything, but the nose is the most effective way to look [for gas]. That is why experts are here with their equipment combing the areas," said Pedro Luis Benítez, the sub-delegate for Mexico's Attorney General's Office, in an interview with the El Universal daily.

British and American investigators ruled out the blast being caused by explosives, as had initially been suspected. Speculation had mounted because the Mexican government didn't give any updates on the evolution of the investigation until late Monday. Officials said that a gas buildup in the basement caused the blast on January 31. Of the 28 people injured who are being treated at various hospitals, six were reportedly still in a serious condition on Wednesday.

Speaking in Querétaro on Tuesday, President Enrique Peña Nieto ordered a thorough investigation "until we know for certain" what occurred. At a ceremony the president offered a moment of silence for the victims and their families.

Experts still don't know what type of gas caused the blast that destroyed four floors of the B2 building, which is located next to Pemex tower. Investigators believe that it could have been methane but won't know for certain until their inquiry is complete. The explosion may have been set off by faulty electrical wiring.