A U.S. Chemical Safety Board go-team has not yet been able to access the portion of DuPont’s La Porte, Texas chemical plant where a release of methyl mercaptan killed four workers early Saturday morning.

CSB Investigator Banks described the area as a five-story high enclosed structure with piping, valves and other equipment.

"DuPont is taking steps to assure the area is safe to access. We will be evaluating that process and when we determine it is safe for our team members to document the site we will enter,” Banks said. “We don't know how soon that will be. We have asked the company to preserve the status of the process, valve and other equipment settings as close as possible to where they were at the time of the accident to aid in our investigation."

The investigation got underway yesterday with a meeting involving the CSB, DuPont and local representatives of the Chemical Workers Union Council. The CSB is interviewing shift workers and other possible witnesses to the events that lead to a release of the highly toxic chemical.

Investigators are also preparing document requests which typically concern maintenance schedules, operator training, equipment histories, hazard analyses and other information critical to determining the root cause of the accident. 

Banks said the CSB will release information to the public as soon as confirmed findings are known.