Accidental production of hydrogen and fire in a silicone manufacturing plant

The event occurred in a silicon hydride (SiH) emulsion production process inside an enclosed production building. The reaction was ongoing when one of the tank started overflowing with foam.
The process generated a flammable gas cloud gas ignited, which later ignited causing an explosion and fire. The shift supervisor ordered to open the garage doors and to turn on forced ventilation to remove the hazy vapour which had started to form.
Before these two actions could take place, the explosion took place.

At the time of the incident there were nine employees onsite. . The explosion caused four fatalities and one injured worker, heavily damaged the production building and its force was felt up to 20 miles away.

According to the CSB preliminary report, various investigations are still ongoing to understand in details the sequence of events of this accident. The most plausible explanation is that the flammable mixture (hydrogen) has been generated by the run-away of a chemical reaction when producing the SiH emulsion. Short before the start of the accidents, the reactor tanks were seen producing a large quantities of foam, typically induced by bulk production of hydrogen in viscous liquids.

The INITIATING cause of the event was the production of a flammable mixture (very probably hydrogen) and its delayed ignition during a chemical reaction process.

Contributing cause were the absence of flammable gas detectors or hydrogen gas detectors able to warn workers. Also the position of the main air mover near the process location and the decision to open the door of the building to remove smoke increased the potential of explosion from flammable gases.

The root cause is very probably to be found in the absence of preventive and mitigating measures tailored to that specific chemical process. This implies an inadequate risk assessment.

silicon-hydrogen reaction tanks

DESCRIPTION OF THE PROCESS
The emulsion in the reactor was made of silane (SiH4) and siloxane polymers. One of the raw materials used to make was emulsion is a methyl-hydrogen polysiloxane copolymer, which is a SiH compound. All these chemicals have the capability of producing large amounts of hydrogen gas under certain conditions (pH, temperature, chemical bonds, total mass, catalysts presents).

The production process had a highly manual was character. It used two atmospheric tanks equipped with agitators. These vessels did not have automatic feeds, requiring operators to add raw materials into the tanks manually. Also the assessment of the quality of the reaction required visual operation.

The explosion heavily damaged the production building. The force from the explosion
was felt up to 20 miles away in the surrounding communities, and some nearby businesses sustained damage from the blast. Post-incident, the plant owner has resumed some of its operations at another location.

The OSHA (see OHSA news release in References) had issued 12 willful regulations violations and proposed a penalty of approximately $1.6 million, due to alleged multiple incidences of electrical violations, including the incorrect electrical classification of the area where the explosion likely originated.
The plant operator contested the allegations.

The CSB report (see references) says that the root cause investigation is still ongoing (checked October 2020).

Nevertheless, from the absence of flammable gas (hydrogen) detection, it can be already concluded that the risk assessment of this process was not foreseeing the possibility of hydrogen evolution, suggesting an inadequate risk inventory and/or the failing of setting the related preventive measures. One of these measure (compliance of electrical equipment and installations in the production approved for hazardous locations) is the reason of the OHSA legal penalty request..