CHARLESTON, W.Va. -- Congressional leaders are pushing the U.S. Chemical Safety Board for a more thorough investigation of the methyl isocyanate stockpiled by Bayer CropScience at the company's Institute plant.

Committee leaders from the House and Senate wrote to board Chairman John Bresland on Monday to ask the board to exercise its authority to broadly examine ways to make chemical manufacturing as safe as possible.

"We believe it is past time to consider whether Bayer's continued use and storage of MIC can be justified in light of the health and safety risks it presents to the surrounding community," said the letter from Senate Commerce Chairman Jay Rockefeller, D-W.Va., and House Commerce and Energy Chairman Henry Waxman, D-Calif. Also signing the letter were Rep. Bart Stupak, D-Mich., and Rep. Ed Markey, D-Mass.

Last month, Waxman's committee, through a subcommittee chaired by Stupak, held a hearing on efforts by Bayer to use anti-terrorism secrecy rules to hide information about the August 2008 explosion and fire that killed two workers at the Institute plant.

Among other things, hearing testimony from Bayer CEO William Buckner revealed that the company had hoped citing the secrecy rules would allow Bayer to avoid a public discussion about its stockpile of more than 200,000 pounds of methyl isocyanate, or MIC, the toxic chemical that killed thousands of people in a 1984 leak in Bhopal, India.

Buckner told lawmakers the company believed "because of safety concerns, we would have been prevented from a full public defense of our safety and security measures and the multiple layers of protection we employ for our MIC processes."

In their letter Monday, Rockefeller and Waxman pointed out again that the August explosion occurred just 80 feet from an above-ground "day tank" where Bayer stores up to 37,000 pounds of MIC.

"The explosion caused an over-pressurized vessel to hurtle violently through the facility, destroying virtually everything in its path," the letter said. "If this vessel had struck the MIC tank, the results could have been a disaster worse than the 1984 Bhopal accident, endangering Bayer employees, emergency first responders, and residents of the surrounding community."

Citing the Chemical Safety Board's broad authority under the Clean Air Act, the lawmakers urged the board to:

Already Bresland has said that the board asked Bayer for copies of any studies "of the feasibility and costs of eliminating MIC from the process or reducing its storage at the Institute site."

But it is not clear in how much detail the board planned to study that issue before issuing a final report later this year. During discussions with the board, Bayer has pushed for the agency not to examine MIC questions at all, let alone in the broad sense now urged by lawmakers.

Since holding a news conference and a public meeting on April 23, both in Institute, board officials have not responded to several requests from The Charleston Gazette to answer a long list of follow-up questions.

But Bresland in an interview Monday that his agency is not letting up on the Bayer probe.

He said board investigators have just received about 4,000 pages of MIC documents from Bayer and are beginning to review them.

"We'll be evaluating those documents and then deciding what steps we need to take," Bresland said. "It's really a logical follow-up to our testimony in Congress and our public meeting."

Bayer spokesman Tom Dover said the company has received the congressional letter and is reviewing it.