DuPont officials told CSB that a braided steel hose connected to a 1-ton capacity phosgene tank suddenly ruptured, releasing phosgene into the air. An operator who was exposed to the chemical was transported to the hospital, where he died the following day.

The phosgene release followed two other release incidents at the same plant this month, including an ongoing release of chloromethane from the plant’s Hexazinone unit, which went undetected for several days, and a release of sulfur dioxide from a spent sulfuric acid unit. The plant announced over the weekend that it would be shutting down a number of process units immediately for safety checks.

“The board is concerned by these releases, which had tragic consequences, and will proceed with an investigation to understand why these unfortunate events occurred,” said CSB Board Member William E. Wright. Wright cautioned that the new case likely would delay efforts to complete other investigations that are being conducted by same investigative team, including those at the Bayer CropScience facility in Institute, W.Va., and an Ohio environmental services company. Including DuPont, the CSB has 17 open investigations, the largest number in its 11-year history.

In voting to approve the investigation, the board noted that the CSB was aware of six other releases from the plant since December 2006. The DuPont Belle complex is a large facility that is regulated under the EPA Risk Management Program and the OSHA Process Safety Management standard because of the volume and hazards of the materials it handles and the potential risk to workers and the community.

According to Scorecard, a pollution watchdog site, water releases of chemicals from the DuPont Belle facility increased by 385 percent from 1988 to 2002. Air releases decreased by 94.3 percent during the same interval. In 2002, Scorecard rated the facility among the dirtiest/worst facilities in the United States for total environmental releases and cancer risk from air and water releases.

CSB investigator Johnnie Banks will lead the four-member team, which is expected at the site on Jan. 26.

The CSB is an independent federal agency charged with investigating serious chemical accidents. The agency’s board members are appointed by the president and confirmed by the Senate. CSB investigations look into all aspects of chemical accidents, including physical causes such as equipment failure as well as inadequacies in regulations, industry standards and safety management systems.

The board does not issue citations or fines but does make safety recommendations to plants, industry organizations, labor groups and regulatory agencies such as OSHA and EPA.