The agency, based on the evidence obtained by CSB investigators, surmised that one of the two workers – employed by Matrix Service Industrial Contractors – died as he climbed or fell into a reactor as he was attempting to retrieve a roll of duct tape during an overnight shift on Nov. 5, 2005.
This was a deadly move, as the reactor was under a nitrogen purge, which is a process that removes oxygen and hazardous gas from equipment by flowing nitrogen through it. A person entering such an environment can be expected to collapse into a coma in less than 40 seconds, with death through asphyxia following soon afterward, CSB said.
The other employee died when he was attempting to rescue his co-worker and was overcome by the oxygen-depleted atmosphere, CSB 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," CSB Board Member John Bresland said.
CSB: Valero Workers Were Not Trained on Hazards of Low-Oxygen Atmospheres
CSB lead investigator John Vorderbrueggen said the agency determined that workers at Valero were not properly trained on the dangers of low-oxygen atmospheres around the unsealed openings of vessels and equipment that are undergoing purges with motionless gases such as nitrogen.
"The CSB Case Study on Valero underscores the importance of strict safeguards when working around low-oxygen environments," Vorderbrueggen said. "Workers are in danger not only inside confined spaces, but also around the opening where inert gases like nitrogen are flowing out."
CSB said it was unable to determine whether the workers knew that the reactor was under a nitrogen purge, but the agency believes the workers were knowledgeable about the rules covering confined space entry.
CSB found that there was a confined space warning sign posted with red warning tape wrapped around the steel bolts surrounding the reactor opening. However, the agency 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."
Valero Has Implemented CSB's Recommendations
In a statement e-mailed to OccupationalHazards.com, a Valero spokesperson said that since the accident, the company has "already implemented, and in some cases exceeded, all four recommendations outlined by [CSB], as well as many other measures to prevent any kind of recurrence in the future."
Valero was urged to conduct safe-work permit refresher training for those who prepare and approve confined space permits, and to conduct confined space control and inert gas purge procedure refresher training for all affected refinery personnel and contractors.
In addition, Valero, as well as Matrix Service Industrial Contractors and the American Petroleum Institute, all were urged to include critical information in training materials for workers, including emphasis that:
- Oxygen deprivation rapidly overcomes victims;
- There is no warning before being overcome;
- Oxygen-deficient atmospheres might exist outside confined space openings; and
- Rescuers must strictly follow safe rescue procedures.
CSB issued a safety bulletin on the hazards of nitrogen asphyxiation in 2003, which cited 80 deaths and 50 injuries from asphyxiation over a period of 10 years ending in 2002.