On May 11, 2022, a significant deflagration occurred at a pilot plant in North Chicago, resulting in extensive damage to the building’s first floor. The explosion originated in a room connected to the chemical drain system, after 100 liters of a hexane-acetone mixture followed by 100 liters of acetone were sent into the facility's chemical drain.
Vapors from these solvents migrated into the subject room through a dry floor drain and formed a flammable vapor cloud, which was subsequently ignited by an unidentified ignition source. The explosion caused substantial mechanical damage but fortunately resulted in no sustained fire. The organization engaged Engineering Systems Inc. (ESi) to investigate the incident, determine the root causes, and provide actionable recommendations to prevent recurrence.
Our Approach
ESi conducted a comprehensive investigation. Using computational fluid dynamics (CFD) modeling, site inspections, and explosion effect analyses, ESi examined circumstances leading to the incident, focusing on how flammable vapors accumulated in the room, identifying contributing factors, and assessing potential ignition sources.
The team identified several factors. The dry p-trap in the floor drain of the room allowed vapors to migrate into the room. Negative pressure created by a wall-mounted exhaust fan enhanced this migration, drawing flammable vapors from the chemical drain system. CFD modeling revealed that the room’s ventilation system failed to mix air thoroughly, leading to the accumulation of a vapor-air layer near the floor. This flammable mixture likely persisted long enough for an ignition source to trigger the explosion.
ESi’s analysis also identified systemic issues that contributed to the incident. Key findings included an inadequate process hazard analysis (PHA) for the chemical drain system, lapses in maintaining the p-trap as a safety barrier, and the non-operational state of the ventilation fan in the chemical lift station. These factors were compounded by a lack of robust management of change (MOC) policies when room function and classification were altered without reassessment of safety features.
Services Utilized
Expertise Utilized
The Outcome
ESi’s investigation provided a comprehensive understanding of the root causes of the incident and delivered actionable insights to mitigate future risks. One of the immediate outcomes was the implementation of corrective measures, including disconnecting chemical drains in non-essential areas and ensuring regular maintenance of critical safety elements such as p-traps and ventilation systems. These steps addressed the immediate vulnerabilities that led to the deflagration.
The operating company also benefited from the enhancement of operational safety through improved management systems. ESi's recommendations prompted the organization to adopt more robust process hazard analysis (PHA) and management of change (MOC) procedures. These improvements aimed to prevent similar incidents by ensuring that potential risks were identified and mitigated during operational or structural changes.
Further attention was given to areas where flammable vapor migration was possible, ensuring that such vulnerabilities were addressed comprehensively. ESi’s insights also supported the operating company in its internal safety reviews and external reporting, helping the company demonstrate a commitment to addressing safety gaps.
By addressing both technical failures and procedural shortcomings, ESi not only helped this operating company improve its safety infrastructure but also ensured the long-term protection of personnel, assets, and operations.
