The two workers died late in the evening of Nov. 6 after they were overcome by nitrogen upon entering a vessel in the hydrocracker complex of the refinery, according to San Antonio-based Valero, the nation's largest refiner.
Company officials still are trying to determine why the two workers, who were contractors from Matrix Services Inc., entered the vessel, which was under a nitrogen atmosphere. The two workers were scheduled to perform work on the hydrocracker complex but were not authorized to enter the vessel, according to the company.
"We are both saddened and dismayed by this incident because we have strict controls that govern entry into confined spaces, especially for vessels with an inert atmosphere," Valero spokesperson MaryRose Brown in a statement. "And, we are conducting a full investigation into this incident so that we can take steps to prevent a recurrence in the future. Our hearts and prayers go out to the family and friends of these two individuals."
CSB investigators Stephen Wallace, P.E., and Francisco Altamirano will gather preliminary information to assess whether the incident warrants further investigation by the agency.
In August 2002, CSB completed a yearlong investigation of a fatal storage tank explosion at the same refinery, then owned by Motiva Enterprises LLC. (For more on that incident, see "Refinery Agrees to a Reduced Fine" and $23.7 Million Motiva Settlement Brings 'Tragic Chapter' to Close.")
In June 2003, CSB issued a Safety Bulletin on the hazards of nitrogen asphyxiation, which identified 85 incidents in the United States between 1992 and 2002 that resulted in a total of 80 deaths and 50 injuries. The bulletin was prompted in part by CSB's investigation of a nitrogen asphyxiation incident at a Union Carbide chemical plant in March 1998; one worker was killed and another severely injured when they entered a large process pipe that was being flushed with nitrogen.