The U.S. Chemical Safety Board (CSB) released a factual update into the May 3, 2019, explosion and fire at AB Specialty Silicones in Waukegan, Ill. The factual update provides a comprehensive incident timeline, detailing the events that led up to the massive explosion and fire that fatally injured four workers and seriously injured another. 

While the CSB’s investigation is ongoing, the 22-page factual update provides details of the incident collected through witness interviews and examination of physical evidence. 

• At the time of the incident, the facility was manufacturing a product referred to as EM 652. EM 652 is AB Specialty Silicones’ 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.
• On the day of the incident, AB Specialty Silicones’ operators were making back-to-back batches of EM 652. AB Specialty Silicones had started the first batch earlier in the week. During the second shift on May 3, the first batch was packaged into storage containers and an operator began production of the second batch. 
• Around 9:30 p.m., a few minutes before the incident, workers told the CSB that the operator making EM 652 began yelling, apparently concerned and frustrated by a problem developing in the EM 652 process. 
• This unusual activity captured the attention of a second operator and the shift supervisor, who ran over to where the EM 652 was being produced. By the time the second operator and the shift supervisor made it to the area, a tank making EM 652 was overflowing with foam. The operator told them that he had just added the first two raw materials of the process into the tank, including XL 10. 
• While the operators and the shift supervisor 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.
• 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. Before an operator was able to turn on the fans, 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. 

Currently, these are the events that the CSB has determined led up to the incident. The investigation team has also documented the scene, finding a number of details that 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. 
• It was determined that there were no flammable gas detectors or hydrogen gas detectors with alarms to warn workers of the significant hazard.

In addition, the CSB noted that the generation of gas in the tank could produce foaming. Foaming does not normally occur during this portion of the EM 652 manufacturing process, however. In addition, 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 continues its investigation.