(CNN)         The fertilizer blamed for the massive explosion that devastated a Texas town in April was kept in wooden bins, in a wooden building, with no sprinklers nearby.And that fell within the existing safety rules for handling ammonium nitrate, a "patchwork" of regulations, recommendations and guidance "that has many large holes," the head of the U.S. Chemical Safety Board told a Senate committee Thursday.The federal agency hasn't found any regulations "that prohibit or discourage many of the factors that likely contributed" to the April 17 explosion in West, Texas, the board's chairman, Rafael Moure-Eraso, told the Senate Environment and Public Works Committee.A fire at the West Fertilizer Company led to an ammonium nitrate explosion that devastated the small town south of Dallas and killed 15 people, most of them firefighters and paramedics. The blast showed up on seismographs as a small earthquake and flattened or damaged dozens of homes, two schools and a nursing home nearby."Facilities like West fall outside the existing process safety standards, which were developed in the 1990s," Moure-Eraso said.Sprinklers aren't required until a company is storing 2,500 tons of ammonium nitrate, he said. And while industry groups have recommended fire safety standards, Texas has no statewide fire codes and most of its counties can't adopt their own."So at West, these fire code provisions were strictly voluntary, and West Fertilizer had not volunteered," he said.Ammonium nitrate is a widely used fertilizer with a notorious reputation as an explosive. The bomb used to blow up the federal building in Oklahoma City in 1995, killing 168 people, was made mostly ammonium nitrate.Moure-Eraso said the Chemical Safety Board urged the Environmental Protection Agency in 2002 to require non-combustible storage bins for reactive chemicals like ammonium nitrate, but the EPA hasn't done that. The committee's chairwoman, California Democratic Sen. Barbara Boxer, said she will be pressuring the EPA to enact those rules."That was a very prescient call, and it didn't happen," Boxer told Barry Breen, the head of the EPA's emergency response arm. The EPA's current guidance for handling ammonium ntirate dates back to 1997, "and I feel that EPA has to step up to the plate here and do a lot more."Fertilizer Plant Fire