On May 3, 2019, at a chemical manufacturing facility in Waukegan, Illinois, the operator of a tank in which a silicon hydride emulsion was being made suddenly yelled a warning. Alerted by the “unusual activity,” another operator and the Shift Supervisor – fellow employees of AB Specialty Silicones – ran over to the emulsions area. By the time they got there, the tank was overflowing with foam.

With those terse details, the factual update released yesterday by the U.S. Chemical Safety Board (CSB) sets the scene for the workplace tragedy which was to follow – a massive explosion that fatally injured four workers and injured another.

The update provides a timeline of the events leading up to the deadly explosion, but not yet a cause. The agency’s investigation is ongoing, and includes interviewing witnesses and examining physical evidence. “Ultimately, we will find the root cause and issue safety recommendations to prevent a similar incident,” said CSB Interim Executive Dr. Kristen Kulinowski.

Under certain conditions...

The blast involved a product named EM 652 – AB Specialty Silicone’s trade name for a silicon hydride emulsion that is used as a water repellent. Under certain conditions, both EM 652 and one of the raw materials used to make EM 652, a compound called XL10, have the capability to produce hydrogen gas. Under certain conditions, hydrogen gas is flammable.

At the time of the incident, company operators were making back-to-back batches of EM 652. A batch made earlier in the week had been packaged into storage containers and production of a second batch had begun.

The tank made a "very strange sound"

When the second operator and Shift Supervisor ran to the tank making EM652 in response to the first operator’s yelling and found foam flowing out of the tank, the first operator told them that he had just added the first two raw materials of the process into the tank, including XL 10.

While the three people were talking, the tank made a “very strange sound” and “erupted.”  Witnesses described a hot and smoky scene as material overflowed from the tank and spilled onto the floor.

According to CSB investigators, the Shift Supervisor directed workers to take actions to ventilate the hazy vapor from the building by turning on exhaust fans and opening the garage doors. But before that could happen, the building exploded, fatally injuring four people. The force from the explosion was felt up to 20 miles away in neighboring communities and damaged surrounding businesses.

Key details

The CSB has identified a number of details which it says are key to the ongoing analysis:

• The instructions to make EM 652 warn of the dangers of the production of hydrogen gas when XL 10 is in contact with acids or bases.
• The EM 652 was made in a set of two atmospheric tanks that were loosely sealed. Workers would open the top of these tanks during the production process to, among other things, perform visual observations. These tanks had no engineered system to direct flammable gas, including hydrogen, to a safe location. 
• The building ventilation system likely caused the flammable gas cloud to mix with air and disperse throughout the building. 
• Finally, the CSB determined that there were no flammable gas detectors or hydrogen gas detectors with alarms to warn workers of the significant hazard. The generation of gas in the emulsions tank could produce foaming; however, foaming does not normally occur during this portion of the EM 652 process. The placement of the main air mover near the EM 652 process further increased the potential explosion danger from flammable gases generated in the emulsions area.

The CSB is an independent, non-regulatory federal agency whose mission is to drive chemical safety change through independent investigations to protect people and the environment. The agency’s board members are appointed by the president and confirmed by the Senate.