Ginnette Riquelme for The New York Times
Workers surveyed the damage that resulted from an explosion at the headquarters of a state-owned oil company, Pemex, in Mexico City Friday.
MEXICO CITY — Hundreds of rescue workers ended their search for survivors on Friday at the site of an explosion that tore through an office building of Mexico’s state-owned oil company a day earlier, as the death toll rose to 33. The head of the company said early indications about the cause suggested that it was an accident.
“All lines of investigation are open; we are not going to discount anything,” said Emilio Lozoya Austin, chief executive of the oil company, Petróleos Mexicanos, or Pemex. “But what it seems like, from what experts can observe, is that it was an accident.”
Mr. Lozoya, at a news conference Friday morning and in interviews throughout the day, emphasized that the investigation was continuing, and that no clear cause had been found. Mexico’s president, Enrique Peña Nieto, visiting a hospital where many of the 120 people who were injured by the explosion were being treated, asked the public to avoid speculating on the cause.
Nonetheless, in a country with little trust in its institutions, the pressure on the government to provide details is mounting as reporters and Twitter users ask pointed questions about why officials have not said what exploded or why. Rumors of bombs and of censored Twitter accounts of Pemex employees swirled online Friday, leading many to note that the blast revealed once again that when there is a lack of transparency, the void tends to be filled with imagined horrors.
“We are all into conspiracy theories,” said Gabriel Guerrero, a political analyst in Mexico City. While the government seems to have communicated relatively well so far, regularly updating the death toll, he said, “the real test will come over the next few days and weeks.”
Independent explosives experts said it often takes more than 48 hours to identify the cause of a large blast that, in this case, collapsed several floors and shattered windows across a wide area. Jimmie C. Oxley, a chemistry professor and explosives expert at the University of Rhode Island, said by telephone that while some forensic investigators may have an idea by now of what happened, it often takes more time to come to a conclusion with colleagues.
All of this is made more difficult by the amount of rubble at the site, Professor Oxley said, noting that photographs posted online showed a tangle of concrete, wires and collapsed floors.
Typically, she said, explosions at buildings are caused by one of two things: gas that is suddenly ignited, or a bomb. Bombs tend to create craters and cratered metal that point investigators to a specific location. If, for example, a basement garage was affected at the Pemex building, Professor Oxley said, investigators would look for signs of a car bomb.
“It’s hard to imagine a bomb carried by a person being very large,” she said.
Gas explosions, like the one that killed several hundred people in Guadalajara in 1992, can be harder to identify because there is not necessarily a single ignition point. Also, Professor Oxley said, since the explosion on Thursday occurred on the lower floors of a building (an administration building near the Pemex tower), “it’s important to know if you had the heating system of the building there, or how that was arranged.”
Government officials have said the blast happened in an area near the base of the building where workers checked their timecards. Before news of the explosion emerged, company officials said there was an electricity problem there, but Professor Oxley said electricity alone would lead to a fire, not an explosion, though if gas had been leaking, a small spark could have been enough to set off a colossal blast.
Still, not all investigations lead to answers. Recalling the case of an explosion at a mall in the Philippines that she was consulted on, Professor Oxley said she could not confirm that there were explosives present based on samples from the scene. “I don’t know there ever was a conclusion,” she said.
