Incompatible Chemical Reaction — Hydrogen Gas Generation and Ignition
AB Specialty Silicones Explosion and Fire
AB Specialty Silicones, LLC
📍 Waukegan, IL
Incident: May 3, 2019  •  CSB Report: September 24, 2021
4
Fatalities
Hydrogen Gas (from Incompatible Chemical Reaction)
Chemical Involved
3
CSB Recommendations
📋 Incident Summary

On May 3, 2019, an explosion and fire at the AB Specialty Silicones chemical manufacturing facility in Waukegan, Illinois, killed four workers and destroyed the production building. An operator inadvertently added an incompatible chemical to a batch reaction tank from a visually identical drum differentiated only by a small label. The addition triggered an uncontrolled reaction generating hydrogen gas inside the building, which accumulated to flammable concentration and ignited.

The CSB found that AB Specialty Silicones was not regulated under OSHA PSM because the chemicals used were below threshold quantities — a regulatory gap allowing the facility to operate without hazard analysis, procedure requirements, and safeguards that might have prevented the incident. The facility had no formal reactive hazard management program, no PHA, and no engineering controls to prevent incompatible chemical mixing or detect accumulated hydrogen.

The September 2021 CSB report issued 3 recommendations, all to AB Specialty Silicones, all closed, focused on reactive hazard identification, chemical storage and labeling, and engineering controls to prevent hydrogen accumulation.

🔎 Key Findings
Finding 01
Operator Added Wrong Chemical from Visually Identical Drum
Two chemicals — one the intended reagent, one incompatible — were stored in visually identical drums with only small label differences as the sole means of differentiation, providing inadequate protection against mis-identification.
Finding 02
Incompatible Reaction Generated Hydrogen Gas Inside Building
The unintended addition triggered a reaction generating hydrogen gas directly inside the enclosed production building — hydrogen accumulated to flammable concentration throughout the space without detection or ventilation.
Finding 03
No Reactive Hazard Management Program or PHA
AB Specialty Silicones had not performed a formal PHA or reactive hazard assessment for batch production processes — the incompatible chemical reaction hazard had never been formally identified.
Finding 04
Facility Below PSM Threshold — Regulatory Gap
The facility was not subject to OSHA PSM because chemicals were below threshold quantities — demonstrating that reactive chemical hazards can be catastrophic at facilities outside PSM regulatory coverage.
Finding 05
No H2 Detection or Ventilation Interlock
No hydrogen gas detection, automated ventilation, or chemical addition interlocks were in place to detect hydrogen accumulation or prevent ignition of the flammable atmosphere.
🔍 Root Causes
1
Incompatible Chemical Hazard Never Identified
The facility had never performed a systematic reactive hazard assessment — the incompatible chemical combination and resulting hydrogen generation hazard were entirely unknown to management and operators.
2
Inadequate Chemical Differentiation Controls
Relying solely on small drum labels to differentiate incompatible chemicals provided no redundant safeguard against mis-identification during production — a single point of failure with catastrophic consequence.
3
No Engineering Controls for Hydrogen Gas Accumulation
No engineering controls (H2 detection, building ventilation interlocks, emergency procedures) existed to prevent ignition of accumulated hydrogen even if the incompatible addition had been recognized after the fact.
☑ CSB Recommendations
→ AB Specialty Silicones (all 3 closed)
Conduct a comprehensive reactive hazard assessment for all batch chemical processes, identifying all chemicals that could react to produce flammable, toxic, or energetic products, and document incompatible combinations in PSI.
→ AB Specialty Silicones
Implement engineering and administrative controls to prevent incompatible chemical additions to batch tanks — including physical separation, distinctive color coding, positive identification verification, and dual-confirmation procedures.
→ AB Specialty Silicones
Install hydrogen gas detection, automatic ventilation, and emergency isolation controls in all production areas where chemical reactions could generate flammable gases — with documented testing and calibration.
💡 Lessons Learned
PSM threshold-based regulation creates gaps for hazardous reactive chemical operations that use individually below-threshold quantities. Any facility handling chemicals that can react to generate flammable or toxic gases needs reactive hazard analysis regardless of regulatory coverage.
Drum labels are the weakest possible differentiation method for incompatible chemicals. Color-coded containers, dedicated storage areas, physical separation, and positive identification requirements are essential controls for preventing incompatible additions.
An uncontrolled hydrogen generation event inside an enclosed building is a building-destroying explosion waiting for an ignition source. Reactive hazard assessment must identify secondary hazards — gas accumulation, confinement effects — not just the immediate reaction.
Process hazard analysis is the tool that allows facilities to discover hazards they did not know existed. A facility that has never done a PHA has unknown hazards that may be fatal.
Chemical addition operations where a wrong chemical can trigger a catastrophe require engineering controls — not administrative controls alone. If the only thing preventing a catastrophe is operator label-reading, the safeguard is inadequate.
PSI: Process Safety InformationPHA: Process Hazard AnalysisSOP: Operating Procedures
🔨 Safety Meeting Toolbox Talk
►Has your facility performed a reactive hazard assessment identifying all chemicals that could react to generate flammable or toxic gases? When was it last updated?
►How are incompatible chemicals stored and differentiated at your facility? If a drum label were missing or misread, what would prevent an operator from adding the wrong chemical?
►Do you have hydrogen detection or flammable gas detection in areas where reactive chemicals are handled? When was this equipment last tested and calibrated?
►If an uncontrolled reaction began generating gas in your production area, what would your operators do? Is there an emergency procedure for this scenario?
►Is your facility subject to OSHA PSM? If not, have you voluntarily applied PHA and reactive hazard assessment to your most hazardous processes?
Immediate Action Items
✓Compile a chemical compatibility matrix for all chemicals used in batch production and identify any incompatible combinations that could generate flammable or toxic gases.
✓Walk your chemical storage areas and verify that incompatible chemicals are physically separated, color-coded, and stored in dedicated areas that prevent cross-contamination.
✓Test your flammable gas detection system in all production areas where chemical reactions occur — verify alarm setpoints, response times, and connection to ventilation and shutdown systems.
✓Brief your operations team on the AB Specialty Silicones incident and ask them to identify any batch addition steps where a wrong chemical could trigger a hazardous reaction.
✓If your facility is not PSM-covered, evaluate whether voluntary application of PHA and reactive hazard assessment for your most hazardous batch processes would identify previously unknown risks.
🔗 PSM Failures Behind This Incident

This incident traced to breakdowns across 3 PSM elements (PSI · PHA · SOP). 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.
Supporting documents in our library →
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 →
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