Loose pipe fittings blamed for sulfuric acid spill at Tesoro refinery in California

The US Chemical Safety Board (CSB) released a technical evaluation report on tubing samples taken from the Tesoro refinery in Martinez, California, concluding that a sulfuric acid spill on February 12, 2014, resulted from insufficient tightening between a tube and a compression joint at a sulfuric acid sampling station.

The spill burned two workers in the refinery’s alkylation unit, who were transported to the nearest hospital burn unit by helicopter.

The spill continued for 2.5 hours, by which time an estimated 84,000 pounds of sulfuric acid was released from equipment onto the refinery grounds and into a process sewer system. Cal/OSHA ordered the process unit to remain shutdown from February 18 until February 28 based on worker testimony that the unit was unsafe.

The Cal/OSHA PSM Unit is also conducting a comprehensive inspection at the Tesoro Refinery with an emphasis on mechanical integrity and operating procedures.

The California Division of Occupational Safety and Health, or Cal/OSHA, participated in this technical evaluation as part of its regulatory investigation.

The incident occurred when the operators opened a block valve to return an acid sampling system back to service. Very shortly after this block valve had been fully opened, the tubing directly downstream of the valve came apart, spraying two operators with acid.

The report, prepared by Anamet -- a California-based materials engineering and laboratory testing firm-- details findings from laboratory examination of the stainless steel tube assembly recovered by Cal/OSHA following the incident. The report concludes that the sulfuric acid spill immediately followed the failure of a 0.75-inch diameter stainless steel tubing connector that came apart due to insufficient tightening of the tube during installation. 

The tube was being pressurized at the time of the incident, and was part of a sulfuric acid sampling station in the refinery’s alkylation unit. The insufficient tightening between the tube and a compression joint allowed the tube to be forced from the joint, most likely by internal pressure. 

Chemical analysis conducted on the tube assembly found that all of its components, including the tube itself, are constructed of Type 316 stainless steel. Type 316 stainless steel is common in industrial processes that require a high level of resistance to corrosion. 

On March 10, 2014, in the same sulfuric acid alkylation unit, two contract workers were sprayed with sulfuric acid while conducting planned maintenance work to remove piping in the alkylation unit. The sulfuric acid sprayed the two workers when they cut into the piping using a portable band saw.

The piping was not drained of process chemicals and was still under pressure, despite the refinery’s issuance of a “hot work” permit for the activity, according to the CSB. Although the contractors were wearing protective suits while performing the work, they were still burned by the acid. 

One worker was exposed when his acid suit got caught on scaffolding as he evacuated from the immediate area. The second worker was burned when acid that remained on his acid suit drained onto his neck during decontamination in the safety shower.

Both workers were taken to a local hospital by ambulance for evaluation and treatment for their chemical burn injuries.

“This incident highlights the need for strong process safety management at facilities that ensures mechanical integrity is verified prior to the introduction of hazardous chemicals into equipment," said CSB chairperson Rafael Moure-Eraso. "However, on March 10, there was another incident that also burned two workers with acid in the same production unit. Four workers burned by sulfuric acid in less than a month clearly demonstrates there are significant opportunities within the refinery for improvement in safety performance.”

In the course of its investigation, the CSB said it identified multiple incidents at the Martinez refinery over the past several years involving the uncontrolled release of sulfuric acid. These include chemical burns to a contract worker in June 2010, an August 2012 incident where two Tesoro workers were sprayed with acid when a temporary hose ruptured and a January 2012 acid release from a failed pump which injured another worker.

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