GAS BLOWDOWN EXPLOSION — CONSTRUCTION PHASE — 6 FATALITIES — NO APPLICABLE REGULATION
Kleen Energy Systems Natural Gas Blowdown Explosion
Kleen Energy Systems, LLC
📍 Middletown, CT
Incident: February 7, 2010  •  CSB Report: May 2012
6
Fatalities
Natural Gas (Methane — Pipeline Purging Operation)
Chemical Involved
12
CSB Recommendations
📋 Incident Summary

On February 7, 2010, six workers were killed and more than 50 others were injured when natural gas vented during a piping cleaning procedure ignited and exploded at the Kleen Energy power plant under construction in Middletown, Connecticut. The procedure — known as a 'gas blow' — involved forcing large volumes of high-pressure natural gas through newly installed piping to clean debris, venting the gas directly to the atmosphere in the vicinity of the occupied construction site.

The CSB investigation found that the gas blow procedure was widely used in the power generation industry but was not governed by any federal or state law, regulation, standard, or code. There was no regulation requiring the area around a gas blow operation to be evacuated or cleared of ignition sources. Gas blown from the piping accumulated near ground level, reached an ignition source, and detonated.

The CSB issued 12 recommendations, including urgent calls for OSHA, state agencies, and standards organizations to regulate gas blowdown procedures and mandate safer alternatives. The Kleen Energy explosion accelerated the development of safer piping cleaning practices in the natural gas power generation industry.

🔎 Key Findings
Finding 01
Gas Blow Procedure Vented Natural Gas Directly to Atmosphere Near Occupied Work Areas
The gas blow procedure used at Kleen Energy involved venting large quantities of high-pressure natural gas directly to the atmosphere in an area surrounded by workers, construction equipment, and ignition sources. No procedure required clearing the area of workers or eliminating ignition sources during the gas blow.
Finding 02
No Federal or State Regulation Governed Gas Blow Procedures
The CSB found that at the time of the explosion, no federal or state law, regulation, standard, or code specifically regulated the gas blow procedure for natural gas power plants. The absence of regulatory requirements allowed an inherently hazardous practice to continue without mandated safeguards.
Finding 03
Large Volume of Natural Gas Reached an Ignition Source and Exploded
The volume of natural gas released during the gas blow accumulated near the ground surface — natural gas, when at sufficient concentration, will form a flammable cloud near grade level before rising. The accumulated cloud reached an ignition source, triggering a deflagration that killed six workers and injured more than 50.
Finding 04
Safer Alternatives to Nitrogen Blowdown Were Available but Not Used
Safer alternatives to gas blowing — including nitrogen purging of piping, which eliminates the flammable atmosphere risk entirely — were available and used in other industries. The power generation industry had not adopted nitrogen purging as a standard practice at the time of the Kleen Energy explosion.
Finding 05
Construction-Phase Process Safety — Risk Not Recognized in Pre-Startup Hazard Review
The gas blow procedure was conducted during the construction and startup phase of the Kleen Energy facility — a period that falls outside OSHA PSM standard coverage but involves significant process safety risk. The hazard of the gas blow was not subjected to a formal hazard review before execution.
🔍 Root Causes
1
Inherently Hazardous Gas Blow Procedure Conducted Without Mandatory Safeguards
The gas blow procedure — which involved releasing large quantities of flammable natural gas to the atmosphere in an occupied area — was conducted without required isolation of ignition sources, worker evacuation, or monitoring for gas accumulation. The procedure was inherently hazardous and no regulation required it to be conducted safely.
2
No Regulation or Industry Standard Required Safer Alternatives or Minimum Safety Measures
The complete absence of applicable regulations or mandatory industry standards for gas blow procedures allowed facilities to conduct this inherently hazardous practice without any mandatory safety measures. The regulatory gap was the enabling condition for the Kleen Energy explosion.
3
No Pre-Procedure Hazard Review Evaluated Gas Blow Risk
The gas blow procedure at Kleen Energy was not subjected to a formal hazard review — such as a job safety analysis or pre-task hazard assessment — that would have identified the risk of gas accumulation and ignition and required mitigating controls.
☑ CSB Recommendations
→ OSHA
Issue a formal guidance document or regulation requiring that natural gas piping purging (gas blow) operations at power plants be conducted only with mandatory safety measures, including area clearance, ignition source elimination, gas monitoring, and use of safer alternatives such as nitrogen purging where practicable.
→ National Fire Protection Association (NFPA)
Develop and publish a code or standard governing gas purging procedures for natural gas piping in power plants, including requirements for area clearance, ignition source control, monitoring, and safer alternative methods.
→ Power Generation Industry / Contractors
Replace gas blow procedures with nitrogen purging or other inert gas purging alternatives for new piping installations; prohibit direct atmospheric venting of natural gas during piping cleaning operations at occupied construction or operating sites.
→ Construction Industry / Engineering Firms
Include formal hazard review — job safety analysis or equivalent — as a required step before any construction-phase gas purging or high-pressure system pressurization procedure at power generation facilities.
💡 Lessons Learned
A procedure that releases large volumes of flammable gas into the atmosphere near an occupied work site is inherently hazardous — and the absence of a regulation prohibiting or controlling that procedure is not evidence that it is safe. The gas blow procedure at Kleen Energy had been used widely in the industry for years without a major incident — until it produced one. The absence of prior incidents is not proof of safety; it is only proof that the consequence had not yet been realized.
Regulatory gaps are process safety gaps. The Kleen Energy explosion occurred, in large part, because no applicable regulation required the area to be cleared, ignition sources to be eliminated, or gas concentrations to be monitored during the gas blow. When a hazardous practice is not regulated, the only protection workers have is the voluntary safety management of the employer. Voluntary safety management is not a reliable substitute for regulatory requirements that establish minimum, enforceable standards.
Safer alternatives — nitrogen purging — were available at the time of the Kleen Energy explosion. Nitrogen purging eliminates the flammable gas hazard entirely. When a safer alternative exists for a hazardous procedure and is not used, the question is not 'why didn't the regulation require it?' but 'why didn't the hazard analysis identify it?' Inherently safer design applies to construction-phase operations as much as to operating processes.
Construction-phase process safety is frequently under-managed. OSHA PSM applies to operating processes — the construction and commissioning period, when facilities are being built and started up, falls largely outside the PSM framework. But the risk during construction and startup is real. Gas blow procedures, pressure testing, and first-fill operations all carry process safety risks that require formal hazard review before execution.
The Kleen Energy explosion accelerated regulatory and industry changes that made the gas blow procedure substantially safer or eliminated it. Six workers died in the process. Process safety lessons extracted from catastrophic events are valuable — but the moral obligation is to anticipate and control hazards before the event, not to regulate them afterward.
SOP: Operating ProceduresPHA: Process Hazard AnalysisEP: Emergency PlanningTRN: TrainingPSSR: Pre-Startup Safety Review
🔨 Safety Meeting Toolbox Talk
►Does your facility have any procedures during startup, commissioning, or maintenance that involve venting large quantities of flammable gas to the atmosphere near occupied work areas? Have those procedures been subject to a formal hazard review?
►When was the last time your facility evaluated whether any routine maintenance or construction procedures could be replaced with an inherently safer alternative — such as substituting nitrogen for natural gas in piping purging operations?
►Do your pre-task hazard assessment and job safety analysis requirements apply to construction-phase operations and commissioning activities at your facility, or only to normal operating procedures?
►Are there any procedures at your facility that are not regulated by OSHA PSM but carry equivalent process safety risk? How does your facility ensure those procedures receive appropriate hazard review?
Immediate Action Items
✓Audit all startup, commissioning, and maintenance procedures that involve venting flammable gases to the atmosphere; identify any cases where gas is vented near occupied areas and require either area clearance protocols or substitution with nitrogen or other inert gas alternatives.
✓Require formal pre-task hazard review — job safety analysis, HAZOP, or equivalent — for all procedures involving high-pressure gas purging, first-fill operations, and pressure testing during construction and commissioning phases.
✓Establish an 'inherently safer alternatives' evaluation requirement in your management of change and pre-startup safety review processes — ensuring that when a procedure involves direct atmospheric release of a flammable material, a safer alternative is formally evaluated.
✓Review your facility's pre-startup safety review (PSSR) requirements to ensure they cover construction-phase hazardous operations including gas purging, pressurization, and first-fill procedures, not only equipment modifications.
🔗 PSM Failures Behind This Incident

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

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.
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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.
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Employee Participation
OSHA PSM requires workers to be meaningfully involved in hazard analyses and procedure development — not just trained on the finished product. Active participation catches gaps that management alone misses.
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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.
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Pre-Startup Safety Review (PSSR)
PSSR is the final checkpoint before hazardous chemicals are introduced into a new or modified system. When PSSR fails or is bypassed, unresolved hazards go live with the process.
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