Cause of deadly chemical leak that killed 4 workers at suburban Houston plant remains unknown

DuPont officials said Sunday it's still not clear what caused a toxic chemical to leak from a valve at a suburban Houston plant, killing four workers and injuring a fifth.

Company spokesman Aaron Woods said DuPont is investigating the cause of the leak of methyl mercaptan at a plant in La Porte. The chemical is used to create crop-protection products such as insecticides and fungicides.

The workers were exposed early Saturday while responding to the leak that started around 4 a.m. and took about two hours to contain. They all were working there as part of their normal shift when the leak happened, Woods said.

The four workers died at the plant and a fifth was transported to a nearby hospital. The injured worker has been released from the hospital.

Woods said company officials are cooperating with local, state and federal authorities in the investigation.

U.S. Chemical Safety Board spokesman Sandy Gilmour said a seven-person investigative team led by the agency's director, Daniel Horowitz, was to arrive at the plant Sunday. Horowitz will be joined by Donald Holmstrom, head of CSB's Western regional office. The CSB is an independent federal agency in charge of investigating chemical accidents.

The chemical, which smells of rotten eggs, also is added to odorless natural gas as a safety measure.

The La Porte plant has 320 DuPont employees. Four other companies are also tenants at the complex.

The emergency manager coordinator for La Porte, Jeff Suggs, said the chemical release was not toxic for those residents, but that it caused an unpleasant odor that people in surrounding neighborhoods could smell.