Despite decades-old warnings about the potential for mass casualties, 50 refineries across the nation still rely on a toxic chemcial known as hydrofluoric acid, or HF. At least 16 million Americans, many of them unaware of the threat, live in the potential path of HF if it were to be released in an accident or a terrorist attack, according to refinery owners' worst case scenario reports. 

Again drawn by a leak of toxic hydrofluoric acid, federal investigators are back at a Texas oil refinery they examined three years ago.

Some nearby residents were told to shelter in place after the release, said Daniel Horowitz, managing director of the U.S. Chemical Safety Board, which has sent a team of investigators to the Citgo refinery in Corpus Christi. It’s not yet clear how much of the acid, known as HF, got out.

“Any incident involving the release of HF is something we take very seriously,” Horowitz said.

A Center for Public Integrity investigation last year found that 50 refineries use the acid despite the availability of safer alternatives. At least 16 million Americans live in the path of a toxic cloud in the event of an accident.

A close call at the Citgo refinery was one of three major accidents involving HF in 2009. The CSB investigated that accident and issued urgent recommendations to Citgo. The board doesn’t have authority to issue citations or impose penalties.

A Citgo spokesman said the company had followed all of the board’s recommendations and that the accident on Monday “is not related to the 2009 incident.”

At about 7:15 p.m. on Monday, a leaking flange released materials including HF from a pipe, triggering water cannons meant to control the release, the Citgo spokesman said. The company’s monitoring data indicated that no chemicals escaped the unit where the leak occurred, he said.

After the 2009 accident, Citgo reported that about 30 pounds of the acid had gotten past its control systems, but the CSB later determined the real amount was likely about 4,000 pounds.

A major U.S. refinery workers’ union says it will make prevention of catastrophic accidents the centerpiece of upcoming contract talks with oil companies. The union abandoned demands for additional safety measures in their last negotiation.

The United Steelworkers, which represents 30,000 workers at petrochemical facilities nationwide, crafted its bargaining position in response to the sorts of disasters and near-misses profiled in the Fueling Fears series by the Center for Public Integrity’s iWatch News.

The series has found that the nation’s aging refineries are plagued by recurring equipment failures and sometimes-fatal fires, explosions and chemical releases that in many cases could have been prevented.

Specifically, the union is focusing on “process safety management” – steps that refineries can take to reduce the risk of catastrophic accidents, including tough self-inspections of equipment and repairing or replacing it when necessary.

“We’ve got time bombs out there, and we want to have a discussion with [oil companies] about it,” United Steelworkers International Vice President Gary Beevers, lead negotiator for the union, said last week. “We’ve got problems in these old refineries and we need changes…Partnering with this industry to make these refineries safer is my number one goal.”