Safety Issues, Troubled History of Del. Refinery Prompt CSB to Continue Inquiry

Pointing to what it believes are "several significant safety issues" that may have contributed to the deaths of two contract workers earlier this month, the U.S. Chemical Safety and Hazard Investigation Board (CSB) said it will continue its investigation at Valero Energy Corp.'s Delaware City, Del., oil refinery.

The two workers died of nitrogen asphyxiation late in the evening of Nov. 6 while performing maintenance on a process vessel in the hydrocracker unit of the refinery.

CSB's John Bresland said Nov. 10 that the agency not only is concerned about the two worker deaths and employee awareness of the hazards of nitrogen but also about the troubled history of the Delaware City refinery, which Valero acquired Sept. 1 when it bought Premocor Refining Group Inc.

Bresland noted that CSB in 2001 investigated a worker death involving a sulfuric acid storage tank explosion at the Delaware City refinery, which was owned by Motiva Enterprises LLC at the time. Motiva Enterprises in September agreed to pay $23.7 million in civil penalties and other costs the largest civil penalty ever collected for environmental violations in Delaware to settle a joint federal-state civil lawsuit stemming from the explosion, which injured several others and caused massive environmental damage. (For more on the settlement, visit

Based on its investigation, Bresland said CSB believes that the two workers who died Nov. 6 were assigned to re-attach piping to a vessel that had been shutdown and was being prepared to be brought online. The vessel contained a catalyst that is sensitive to oxygen and moisture, and nitrogen was added to the vessel to prevent moisture from reaching the catalyst, Bresland said.

"It appears that one of the two contractor employees likely became disoriented, passed out and fell into the vessel after he breathed nitrogen near the manway opening on top of the vessel," Bresland said. "The manway was also the location on the vessel where the process piping was to be re-attached. Witnesses report that the contractor employee had been reaching into the vessel, attempting to retrieve debris that was inside it.

"Witness statements indicate that upon seeing his colleague fall into the vessel, the second contractor employee then entered it, probably in an attempt to save his co-worker. Both men died quickly from nitrogen asphyxiation."

Bresland added that CSB has not determined if the two workers, who were contractors from Matrix Services Inc., knew that the vessel contained nitrogen.

"If they did know it contained nitrogen, we are unsure whether they were aware of its serious hazards," Bresland said.

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