Leaking and uncontained hydrogen led to an explosion that killed four workers and seriously injured a fifth last May at AB Specialty Silicones in Waukegan, Illinois, according to a preliminary investigation report released by the US Chemical Safety and Hazard Investigation Board on Dec. 18.
The plant made custom silicone products that are used in a wide variety of industries, including personal care, chemical manufacturing, adhesives, sealants, and coatings. It ran 24 hours a day and employed 88 people who worked in three shifts.
However, despite the output, the quantities of material the facility used and stored fell below threshold levels triggering oversight by the US Environmental Protection Agency’s Risk Management Program or the Occupational Safety and Health Administration’s process safety management standard, the CSB says.
The hydrogen explosion took place in an area where the company made a silicon hydride emulsion. The blast was felt 30 km from the facility.
One of the products that the company was making in the emulsions area at the time of the incident was an SiH emulsion called EM 652, according to the CSB. EM 652 is an emulsion of silane and siloxane polymers and was held in a tank that was neither sealed nor vented to a safe location. One of the raw materials used was a methylhydrogen polysiloxane copolymer called XL10.
XL10 and EM 652 can produce explosive amounts of hydrogen gas under certain conditions, the CSB says.
The building was not equipped with functioning detectors for hydrogen or other flammable gases. While the building filled with flammable vapors, the workers attempted to open the emulsion area to outside air and turn on fans. They were unable to complete these efforts before the building exploded.
At a press briefing, CSB Interim Executive Authority Kristen Kulinowski emphasized that the update report was only preliminary. The CSB expects to release the full report late next year. Kulinowski said it was likely the final report would closely examine the regulatory system affecting manufacturing efforts involving silicon.
In a recent statement, AB Specialty Silicones says it commissioned a private independent study that determined the root cause to be “human error that resulted in the mistaken addition of an erroneous ingredient.” It has provided this study to the CSB, the company says.
This story was revised on Dec. 23, 2019, to add a statement from AB Specialty Silicones.