Federal officials issued urgent new safety recommendations Wednesday for a Texas oil refinery where 21 tons of deadly acid were released this summer and said they are investigating the use of the chemical at refineries nationwide.

The head of the U.S. Chemical Safety Board said the inquiry continues into the July accident at Citgo's Corpus Christi refinery that seriously injured a worker, and accidents involving hydrofluoric acid in Illinois and Pennsylvania are also being investigated. In all, about a third of the nation's 150 refineries use hydrofluoric acid, or HF, in the process of making high-octane gas.

"We're looking industrywide at the HF use in refineries and the safety of HF at the 51 refineries," CSB investigations supervisor Robert Hall said.

The United Steel Workers union and the Sierra Club have been urging a ban on the acid for months, saying it's too dangerous to workers and people who live nearby. The highly corrosive acid can burn eyes, eat away flesh at a rapid rate and is fatal after prolonged exposure.

At the Corpus Christi plant, a control valve failed July 19 and released an HF vapor cloud. That cloud caught fire and started explosions that released the additional 21 tons of acid vapor, about 2 tons of which escaped into the sky. The injured worker got caught up in the cloud. Winds helped carry the massive cloud into the ship channel and away from people.

The CSB was critical of Citgo's lack of cooperation with investigators, its objection to the public release of surveillance video of the incident and its early reports to state regulators that only 30 pounds of HF escaped into the sky.

"We believe the original release was at least 100 times larger than Citgo had originally stated," said Hall.

Citgo, a Houston-based refiner and subsidiary of Venezuela's national oil company, said in a statement that it is cooperating and has already taken action on the recommendations.

"We hold nothing in higher regard than the safety of our employees and members of the local community," said the company, which said its HF calculations were based on air samples and that its reluctance to release the video was for security purposes.

The Texas Commission on Environmental Quality has "significant concerns" about Citgo's reporting, spokeswoman Andrea Morrow said, and the agency's investigation is pending.

The CSB recommended that Citgo upgrade its emergency water system within 30 days. The system is used to spray down and absorb HF if it escapes, but the board's investigation found the refinery nearly ran out of water after the first day and had to start using salt water from the ship channel.