A refinery fire that killed two employees at the BP-Husky Toledo complex in Oregon, Ohio, Sept. 20, 2022, started after liquid naphtha made its way through piping intended only for gas before forming a vapor cloud and igniting, says the U.S. Chemical Safety and Hazard Investigation Board (CSB) in an investigation update released June 13.
The naphtha entered the piping after multiple system failures led to unstable operating conditions. Earlier in the day, a drain valve failed and leaked 63,625 pounds of naphtha. Workers stabilized the situation by shutting down and bypassing several operating units. Later in the day, a worker discovered a seal leak on a crude oil pump. The worker shut down the pump, which triggered another pump to increase speed to maintain the feed flow rate for the crude unit.
What followed was a series of events that redirected the flammable naphtha to a storage vessel called a mix drum that typically contains vapor. The drum began overfilling, sending liquid naphtha through what was normally vapor piping to various refinery furnaces and boilers. Four workers began draining the drum to a flare and oily water sewer system. Shortly after, two of the workers left, and the remaining two workers began draining liquid from the drum to the ground while wearing self-contained breathing apparatus.
A worker in a nearby fluid catalytic cracking unit told CSB they saw two workers near the drum along with a visible vapor cloud forming on the ground. An approaching rainstorm shifted the wind, which likely directed the nearby Crude 1 furnace, igniting the vapor cloud.
“Within seconds, the area around the mix drum and nearby Crude 1 Unit equipment was engulfed in a large fire,” CSB states in its report. “The fire fatally burned the two workers who were responding to the level in the mix drum.”
The refinery emergency response team spent three hours containing the fire and closing numerous valves to isolate the naphtha leaking from the drum.
In its report, CSB noted that in 2018 the refinery commissioned a new $115 million coker gas plant to reduce the environmental impact of its operations. The plant removes sulfur and light hydrocarbon compounds from the gas produced in the coker units before it goes to the mix drum. The flammable liquid naphtha from the Crude 1 Unit reached the drum by flowing through piping associated with the new coker gas plant.
CSB is continuing to investigate the incident at the refinery, now owned by Cenovus Energy Inc. after its 2021 merger with Husky Energy and renamed Ohio Refining Company LLC. CSB is looking at several areas of operations, including the hierarchy of controls, human factors for process plant operations, management of abnormal situations and regulations, industry standards and guidance.
“While the CSB’s investigation is still ongoing, we want to provide the public with important factual details surrounding this tragic incident as we know them now,” said CSB chairperson Steve Owens in a news release. “Our investigation will use this and other information that we gather to make findings and recommendations to help prevent a similar tragedy from occurring in the future.”
