Torrance, CA– An ongoing investigation by the U.S. Chemical Safety Board (CSB) of the February 18, 2015, explosion at the ExxonMobil Refinery in Torrance, California, has uncovered multiple process safety management deficiencies that led to the accident and a serious near miss.
Investigators found that the explosion could have been prevented if managers had taken into account aging safety equipment and shut down a key, spark-generating part of the refinery before attempting repairs elsewhere, federal investigators said.
The unit being repaired had operated for five years without a maintenance overhaul and, as a result, a key valve failed and leaked volatile hydrocarbons into an electrostatic chamber where the material combusted, the U.S. Chemical Safety and Hazard Investigation Board said.
The resulting fireball injured four contractors, destroyed a large part of the refinery and sent a fine white ash raining down on nearby homes and cars.
The blast also shook nearby homes and tossed an 80,000-pound piece of equipment within feet of another unit where tens of thousands of pounds of a highly volatile and toxic substance called modified hydrofluoric acid, or HF, are stored in tanks.
The blast knocked over a column that contained a laser sensor dedicated to detecting a leak of the acid, investigators said.
The CSB also found that large pieces of debris from the explosion were thrown into other units of the refinery directly surrounding the ESP. One of these pieces of debris hit scaffolding in the refinery’s alkylation unit, narrowly missing a tank containing tens of thousands of pounds of modified hydrofluoric acid, or HF. The CSB determined that had the debris struck the tank, a rupture could have been possible, resulting in a potentially catastrophic release of extremely toxic modified HF into the neighboring community.
CSB Chairperson Vanessa Allen Sutherland said, “Hydrofluoric acid can pose a severe hazard to the population and environment if a release occurs. After HF acid vaporizes it condenses into small droplets that form a dense low-lying cloud that will travel along the ground for several miles and can cause severe damage to the respiratory system, skin, and bones of those who are exposed, potentially resulting in death.”
Torrance, California is a mixed-use city with industrial areas directly adjacent to residential communities. Within a three-mile radius of the ExxonMobil refinery are 333,000 residents, 71 schools, and eight hospitals. In an area as heavily populated as Torrance, a significant release of modified HF stored at ExxonMobil has the potential to cause serious injury or death to many community members.
CSB investigators have faced a lack of cooperation from ExxonMobil to comply with their requests for information about the near miss incident involving the alkylation unit and modified HF even after repeated voluntary requests and subpoenas. To date, the CSB has no or incomplete responses to 49% of its subpoena requests. Chairperson Sutherland said, “Despite these challenges, the team is making strides to complete their investigation, including analysis of the near miss incident.”
With the FCC unit shut down, steam was forced into a reactor to prevent hydrocarbons from flowing back from the main distillation column. On the morning of the accident, this steam was escaping through an open flange on the expander, preventing operators from continuing their maintenance work. It had traveled through a leaking slide valve connected to the reactor.
An outside supervisor then reduced the amount of steam being forced into the reactor so that work could continue. However, at the time, workers were unaware that hydrocarbons were leaking into the main distillation column from interconnected equipment. As the pressure of the steam dropped, the hydrocarbons flowed back into the reactor, out through the leaking slide valve and eventually into the ESP. There the hydrocarbons found an ignition source – and exploded.
Also, ExxonMobil performed inadequate process hazard analyses, which could have identified more effective safeguards against the flow of hydrocarbons, such a blind or de-inventorying the main distillation column. Investigator-in-charge Mark Wingard said, “Although our investigation found two different process hazard analyses that considered a combustible mixture igniting in the electrostatic precipitator, no effective safeguards were implemented at the refinery to mitigate this threat.”
The failure to conduct a management of change review or perform a hazards analysis for this non-routine work is similar to the circumstance surrounding other CSB refinery investigations, including the August 6, 2012, fire at the Chevron Refinery in Richmond, California. That fire endangered 19 workers and sent more than 15,000 residents to the hospital for medical attention. In a final report on that accident, the CSB proposed recommendations for substantial changes to the way refineries are regulated in California.
The agency also added process safety management reform to its list of most wanted safety improvements.