CSB Issues Case Study in Fatal 2005 Valero Refinery Delaware City Accident
November 13, 2006 // Published as a news service by IHS
The study concluded that the accident in which two workers were asphyxiated inside a nitrogen filled confined space could have been avoided through better hazard awareness training and proper confined space rescue actions.
The accident occurred at the Valero Energy Corporation Refinery in Delaware City, Del. on Nov. 5, 2005 during the overnight shift.
The workers, employed by a contractor, Matrix Service Industrial Contractors Inc., were engaged in reinstalling a large pipe elbow on the top of a pressure vessel, called a hydrocracker reactor.
The uninstalled pipe left an opening on a work platform 24 inches in diameter, surrounded by two foot high steel bolts. The reactor was under a nitrogen purge - a process that removes oxygen and hazardous gas from equipment by flowing nitrogen through it.
The CSB determined that after the workers noticed a roll of duct tape inside the reactor on a tray about five feet below the opening they attempted to remove it with a long wire hook.
Entering the vessel to retrieve the tape under Valero safe work rules would have required getting a specially equipped and trained crew because the vessel was a permit required confined space as defined by OSHA.
That would delay the elbow reassembly many hours, but the job was supposed to be completed by the end of the shift. Repeated attempts by one of the workers to remove the tape were unsuccessful.
Subsequently, the CSB concluded that he most likely stepped over the bolts and sat on the narrow ledge around the opening, presumably to improve his chance of hooking and removing the tape.
At this point, based on the evidence obtained by CSB investigators, there were two reactor entry scenarios: In scenario one, the worker intentionally entered the reactor by lowering himself through the opening, intending to grab the tape and quickly climb back out with the aid of a co-worker standing on the platform.
But the environment created by the nitrogen flow in the reactor quickly overcame him, and he collapsed. In the second scenario, the worker may have simply slipped off the narrow ledge into the reactor, or was overcome by the oxygen depleted atmosphere directly above the opening, lost his coordination or possibly lost consciousness and slid in.
Seeing his co-worker lying on the tray five feet down inside the reactor, a second worker quickly inserted a ladder through the opening and climbed inside. He too was overcome by the oxygen depleted environment and also succumbed. Efforts by emergency responders to revive the men were unsuccessful and the men were declared dead at a hospital.
CSB board member John Bresland said, "This accident is a telling example of improper entry into a confined space, and we found that workers are not adequately warned that hazardous atmospheres might exist around unsealed confined space openings."
Bresland said that this is not a new issue, noting the CSB issued a safety bulletin on the hazards of nitrogen asphyxiation in 2003. That bulletin cited 80 deaths and 50 injuries from asphyxiation over a period of 10 years ending in 2002.
Lead Investigator John Vorderbrueggen said the CSB determined that workers at Valero and elsewhere are not properly trained on the dangers of low oxygen atmospheres around the unsealed openings of vessels and equipment that are undergoing purges with inert gases such as nitrogen.
"The CSB Case Study on Valero underscores the importance of strict safeguards when working around low oxygen environments. Workers are in danger not only inside confined spaces, but also around the opening where inert gases like nitrogen are flowing out," Vorderbrueggen said.
The report emphasizes the dangers to rescuers who go into such spaces to save their co-workers. "It is a perfectly natural human reaction," said Vorderbrueggen, "but it must be resisted at all costs. It is impossible for humans to hold their breath long enough to survive in such low oxygen environments, and frequently these types of accidents involve a series of workers succumbing while trying to help their colleagues."
An oxygen meter inserted into the reactor after the accident measured less than 1% oxygen in the atmosphere. Normal breathing air is about 21% oxygen and 78% nitrogen. When the oxygen level drops below about 19% humans begin to be impaired almost immediately.
The CSB was unable to determine whether the workers knew that the reactor was under a nitrogen purge. But they were knowledgeable about the rules covering confined space entry.
The CSB found that in the Valero reactor opening had a confined space warning sign posted with red warning tape wrapped around the steel bolts surrounding the opening, properly alerting the workers of the permit required confined space.
However, the CSB determined it was only after the accident that the company put up a barricade around the work area with a sign reading "Danger - Nitrogen/Inert Gas Purge in Progress - Oxygen Deficient Atmosphere - Do Not Pass This Point Without Authorization."
"Warning signs and barricades are additional protection for workers tempted to enter low oxygen environments," Bresland said, "But they are only a supplement to strict company enforcement of confined space entry rules and proper training on the hazards of nitrogen purges and oxygen-deficient atmospheres."
The CSB makes several recommendations to the Valero Refinery, to the Valero Energy Corp., to Matrix Service Industrial Contractors Inc. and to the American Petroleum Institute (API), the industry's principal trade association.
Similar recommendations are made to the American Society of Safety Engineers (ASSE) and the Compressed Gas Association.
Valero was urged to conduct safe work permit refresher training for confined space permit preparers and approvers and to conduct confined space control and inert gas purge procedure refresher training for all affected refinery personnel and contractors.
Recommendation recipients were urged to include critical information in training materials for workers, including:
- Oxygen deprivation rapidly overcomes victims.
- There is no warning before being overcome.
- Oxygen deficient atmospheres might exist outside confined space openings.
- Rescuers must strictly follow safe rescue procedures.