HYDROGEN EXPLOSION — CHEMICAL INCOMPATIBILITY — 4 FATALITIES — FACILITY DESTROYED
AB Specialty Silicones Hydrogen Explosion and Fire
AB Specialty Silicones, LLC
📍 Waukegan, IL
Incident: May 3, 2019  •  CSB Report: April 2022
4
Fatalities
Hydrogen (Generated by Incompatible Chemical Reaction)
Chemical Involved
9
CSB Recommendations
📋 Incident Summary

On May 3, 2019, four workers were killed and one was injured when an explosion destroyed the production facility of AB Specialty Silicones, LLC in Waukegan, Illinois. The explosion occurred after an operator pumped an incorrect chemical into a manufacturing tank — a chemical that was incompatible with another substance already in the tank. The incompatible chemicals reacted, producing hydrogen gas that accumulated in the production building and ignited.

The CSB found that the incorrect chemical was stored in a drum nearly identical in appearance to the correct chemical — the only distinguishing feature being small labels and bung caps. The production building had no hydrogen gas detectors, no flammable gas detection system, and no engineered pathway to direct hydrogen gas produced in the process to a safe location.

The explosion destroyed the AB Specialty Silicones facility entirely and caused extensive damage to adjacent businesses. The incident illustrates the deadly combination of chemical incompatibility hazards, inadequate detection systems, and reliance on visual label inspection as the sole barrier against wrong-chemical addition.

🔎 Key Findings
Finding 01
Operator Added Wrong Chemical to Tank — Identical Drum Appearance Was the Root Cause
The operator pumped an incorrect chemical into the manufacturing tank because it was stored in a drum that was nearly identical in appearance to the correct chemical — the only difference being small labels and bung caps. No engineered safeguard prevented addition of the wrong chemical.
Finding 02
Incompatible Chemicals Reacted to Produce Hydrogen Gas in an Enclosed Building
The incompatible chemicals reacted in the open-top manufacturing tank, producing hydrogen gas. The building's ventilation system dispersed the hydrogen throughout the enclosed production building rather than exhausting it safely — creating a flammable atmosphere throughout the occupied space.
Finding 03
No Hydrogen or Flammable Gas Detectors in the Facility
AB Specialty Silicones had no hydrogen gas detectors or flammable gas detection system with alarms in the production building. Workers had no warning that a flammable atmosphere was developing — providing no opportunity to evacuate before the hydrogen reached an ignition source.
Finding 04
Open-Top Tanks Had No Engineered System to Direct Flammable Gas to Safe Location
The manufacturing tanks were open-top vessels with loose covers. There was no engineered system — such as a vent to a safe outdoor location or a scrubber — to direct hydrogen gas generated during the process away from the occupied production building.
Finding 05
Chemical Hazard Information Warned of Hydrogen Generation — Not Acted Upon in Design
Product formulation instructions for the EM 652 product being manufactured explicitly warned that mixing XL-10 catalyst with acids or bases would produce hydrogen gas. This known hazard was not translated into engineering safeguards, gas detection requirements, or adequate chemical identification controls.
🔍 Root Causes
1
Wrong Chemical Added Due to Inadequate Chemical Identification Controls
The fundamental cause of the chemical incompatibility event was the addition of the wrong chemical — enabled by storing incompatible chemicals in near-identical drums with only small label differentiation. No engineered control, procedure, or physical safeguard prevented wrong-chemical addition.
2
No Detection or Ventilation Safeguards for Hydrogen Gas in the Production Building
After the incompatible chemicals were mixed, there was no gas detection system to warn workers of the accumulating hydrogen, and no engineered ventilation or venting system to direct hydrogen out of the occupied building. The absence of these safeguards made evacuation impossible — workers had no warning before ignition.
3
Known Chemical Incompatibility Hazard Not Incorporated Into Facility Design or Procedures
Product documentation warned of hydrogen generation when XL-10 contacted acids or bases. This known hazard was not incorporated into facility design (vent systems, gas detection, physical separation of incompatible chemicals) or into written procedures that would have prevented the wrong-chemical addition.
☑ CSB Recommendations
→ AB Specialty Silicones / Industry
Implement physical differentiation controls for drums containing incompatible chemicals — including color coding, unique container shapes, locked storage with access controls, or other safeguards that make wrong-chemical addition physically difficult rather than relying solely on label reading.
→ AB Specialty Silicones / Industry
Install hydrogen gas detectors with audible and visual alarms in all production areas where hydrogen-generating chemical reactions can occur; establish alarm setpoints that provide adequate warning time for evacuation before the lower flammable limit is reached.
→ AB Specialty Silicones / Industry
Install engineered venting systems on tanks where hydrogen-generating reactions can occur; vent hydrogen to a safe outdoor location or through an appropriate treatment system rather than allowing generated gas to accumulate in the occupied building.
→ OSHA / Industry
Require that chemical incompatibility hazards identified in Safety Data Sheets and product formulation documentation be systematically evaluated during process hazard analysis — including identification of engineering controls needed to prevent incompatible chemical mixing and to manage generated hazardous gases.
💡 Lessons Learned
Relying on label reading as the only barrier against adding the wrong chemical to a hazardous process is not a reliable safeguard. Labels can be misread, overlooked, or — as at AB Specialty Silicones — be nearly identical for incompatible chemicals. Engineered physical differentiation — different container colors, shapes, connection types, or locked-access storage — is required when wrong-chemical addition would produce a hazardous consequence.
Hydrogen is a colorless, odorless, and extremely flammable gas with a wide flammability range (4%–75% in air). When hydrogen is produced inside an occupied building, the time between accumulation above the LFL and an ignition event can be very short. Gas detection with alarms is not optional in spaces where hydrogen can accumulate — it is the primary warning that allows workers to evacuate before a source of ignition is reached.
Open-top vessels in a production building that can generate flammable or toxic gases are a fundamental containment failure. The generation of hydrogen inside a loose-covered tank in an occupied building — without any engineered pathway to direct the gas to a safe location — meant that the production building became the accumulation vessel. Any process that can generate a hazardous gas must have an engineered system to manage that gas away from occupied areas.
Known chemical hazards documented in Safety Data Sheets and product formulation instructions must be translated into facility design and operating procedures. The fact that the formulation for EM 652 explicitly warned of hydrogen generation when XL-10 contacted acids or bases — and that this warning had not been incorporated into engineering controls, gas detection, or chemical separation requirements — represents a systematic failure to apply available hazard information.
The complete destruction of the AB Specialty Silicones facility and the damage to adjacent businesses demonstrate that an explosion in a production building does not respect property boundaries. Small specialty chemical facilities are not exempt from the principle that chemical incompatibility hazards must be engineered out or controlled — the consequence of ignoring them is the same regardless of the facility's size.
PSI: Process Safety InformationPHA: Process Hazard AnalysisSOP: Operating ProceduresMI: Mechanical IntegrityTRN: Training
🔨 Safety Meeting Toolbox Talk
►Does your facility use chemicals that are incompatible with each other? Are those chemicals stored and handled in a way that makes wrong-chemical addition physically difficult — through physical differentiation, segregated storage, or engineered controls beyond label reading?
►If any reaction in your process can generate hydrogen or other flammable gases, do you have gas detectors with alarms in the production area? Are alarm setpoints set to warn workers before the lower flammable limit is reached?
►Are your process tanks equipped with engineered systems to manage gas generated during production — including venting to a safe outdoor location or treatment system — rather than allowing generated gases to accumulate in the occupied building?
►How does your facility translate chemical incompatibility hazards documented in Safety Data Sheets into engineering controls and operating procedures? Is there a systematic process to ensure hazard information reaches facility design and PHA review?
Immediate Action Items
✓Audit storage and handling of all chemicals that are incompatible with other chemicals used at your facility; identify cases where incompatible chemicals are stored in similar containers or could be confused; implement physical differentiation controls before the next operation involving those chemicals.
✓If any process at your facility can generate hydrogen, methane, or other flammable gases inside an occupied building, conduct an immediate assessment of gas detection coverage; install detectors with audible and visual alarms where gaps exist.
✓Review all process vessels and tanks that are open-top or loosely covered and can generate flammable or toxic gases; evaluate whether engineered venting to a safe location is needed and implement where required.
✓Incorporate chemical incompatibility hazard review into your next PHA or pre-startup safety review; confirm that known incompatibilities documented in SDSs are mapped to engineering controls, procedural safeguards, and detection systems.
🔗 PSM Failures Behind This Incident

This incident traced to breakdowns across 5 PSM elements (PSI · PHA · SOP · MI · TRN). Each represents a documented gap that process safety documentation and consulting can close before a similar event occurs at your facility.

Process Safety Information (PSI)
Accurate, complete Process Safety Information is the foundation every other PSM element depends on. When PSI is missing or wrong — chemistry data, equipment specs, P&IDs — the entire hazard analysis is built on a flawed base.
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Process Hazard Analysis (PHA)
A structured PHA or HAZOP study exists to identify exactly these scenarios before they occur. When PHA is absent, superficial, or overdue for revalidation, hazards operate unseen until they kill someone.
Supporting documents in our library →
Operating Procedures (SOPs)
Operators cannot reliably hold safe operating limits without clear, current, enforced procedures. Deviation from acceptable operating conditions — a root cause here — is a direct consequence of SOP failure.
Supporting documents in our library →
Mechanical Integrity (MI)
Equipment must be designed, inspected, and maintained to operate safely in its intended service. Mechanical integrity failures — degraded equipment, missed inspections, deferred repairs — contributed to loss of containment here.
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Training & Operator Competency
Workers must understand process hazards — not just the steps on the page. Training records, refresher frequency, and verified competency are all OSHA PSM requirements that gaps here violated.
Supporting documents in our library →
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