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Kleen Energy Natural Gas Explosion

Overview

On February 7, 2010, Kleen Energy, a combined-cycle natural gas-fueled power plant under construction in Middletown, Connecticut, experienced a catastrophic natural gas explosion during planned cleaning of fuel gas piping using a "gas blow." Six workers were fatally injured and at least 50 others were injured. The CSB concluded that releasing large volumes of natural gas in the vicinity of workers or ignition sources is inherently unsafe and identified safer alternatives to natural gas blows.

Incident Snapshot

Field Value
Facility / Company Kleen Energy
Location Middletown, CT
Incident Date 02/07/2010
Investigation Status CSB final report approved at a public meeting in Portland, CT, on June 28, 2010.
Accident Type Flammable Vapor Investigation
Final Report Release Date 06/28/2010

What Happened

  • Workers were conducting a "gas blow" to clean fuel gas piping by forcing natural gas through the piping at high pressure and volume to remove debris.
  • A total of 15 natural gas blows were completed intermittently over approximately 4 hours through a number of open-ended pipes located less than 20 feet off the ground.
  • At the time of the explosion, natural gas was being blown from an open-ended pipe between two large structures, known as heat recovery steam generators (HRSGs), in an area immediately south of the power generation building.
  • Approximately 480,000 standard cubic feet of natural gas were released outdoors near the building in the final 10 minutes before the blast.
  • Just over 2 million standard cubic feet of natural gas were released in total over the course of the morning.
  • At approximately 11:15 a.m., the released natural gas found an ignition source and exploded.

Facility and Process Context

  • Kleen Energy was a combined-cycle natural gas-fueled power plant under construction in Middletown, Connecticut.
  • The incident occurred during the commissioning and startup phase of the Kleen Energy project.
  • The planned work activity was cleaning fuel gas piping during plant startup.
  • The vent pipes were adjacent to the south wall of the main power generation building at the site.
  • The location was outdoors but congested by the surrounding power generation equipment.
  • The vent pipe itself was installed in a relatively horizontal orientation.
  • More than 50 people were working inside the power generation building at the time of the explosion; only about 15 of the 50 were actually involved in the natural gas blow activities.

Consequences

  • Fatalities: 6
  • Injuries: at least 50
  • Environmental release: Approximately 2 million standard cubic feet of natural gas were released over the course of the morning; approximately 480,000 standard cubic feet were released outdoors near the building in the final 10 minutes before the blast.
  • Facility damage: Catastrophic natural gas explosion at the plant; the incident occurred in a congested area near the power generation building.
  • Operational impact: The explosion occurred during commissioning and startup activities and killed six workers and injured at least 50 others.

Key Findings

Immediate Causes

  • At approximately 11:15 a.m., the released natural gas found an ignition source and exploded.

Contributing Factors

  • The pipe cleaning crew did not have a safety meeting that specifically discussed the hazards of natural gas blows.
  • The pipe cleaning crew did not receive and review the natural gas blow procedure.
  • Efforts were made to eliminate or control potential ignition sources outside of the power generation building, but ignition sources remained outside and inside.
  • The gas blows themselves could have been self-igniting due to expelled debris creating a spark or through static accumulation from the flow of the gas.
  • Electrical power to the building was on, welders were actively working, and diesel-fueled heaters were running.
  • The congested area and the orientation of the vent pipe likely adversely affected the dispersion of the natural gas.
  • Some workers were informed that natural gas blows would be occurring on February 7, while others did not learn about the planned natural gas blows until they reported to work that morning.
  • Some contractors were instructed to continue working inside the power generation building during the natural gas blow activities, while other groups were directed to leave while the work was being completed.
  • A few individuals made the personal decision to vacate the building because they were alarmed by the smell of the natural gas odorant.
  • The CFR target for the fuel gas piping at the Kleen Energy site was greatly exceeded, and significantly more natural gas was released than was actually needed to remove debris from the piping.

Organizational and Systemic Factors

  • The CSB determined that no specific federal workplace safety standards prohibit intentional releases of natural gas into workplaces.
  • The electric power generation sector and related industry associations do not currently operate a safety standards development program or publish industry-recognized safety standards.
  • No recognized good practice safety standards or technical guidelines address the conduct of cleaning power plant fuel gas piping.
  • There are no OSHA regulatory requirements for workers to participate in developing procedures or training related to fuel gas safety.
  • The Connecticut Governor’s Commission found that no agency regulated the process used, or any process that might be used such as gas purging, to clean the natural gas pipeline that was the source of the explosion.
  • The National Fuel Gas Code, NFPA 54/ANSI Z223.1, did not apply to fuel gas piping systems like the one at Kleen because its scope exempted power plants and piping systems with operating pressures greater than 125 pounds per square inch gauge (psig).
  • NFPA 37 and NFPA 850 did not address safe practices for cleaning fuel gas piping.
  • ASME B31.1 did not prohibit natural gas blows and did not provide guidance about the technical or safety aspects of pipe cleaning procedures or operations.

Failed Safeguards or Barrier Breakdowns

  • The pipe cleaning crew did not have a safety meeting that specifically discussed the hazards of natural gas blows.
  • The pipe cleaning crew did not receive and review the natural gas blow procedure.
  • Efforts to eliminate or control potential ignition sources were incomplete because ignition sources remained outside and inside.
  • The vent piping lacked adequate technical evaluation to ensure adequate air mixing and that the release was directed to a safe location.
  • Instructions to control or eliminate potential ignition sources were ill-defined.
  • No OSHA standard addressed the safe handling of natural gas or the hazards of methane.
  • OSHA regulations did not expressly prohibit the planned release of flammable gas in the vicinity of workers.
  • The codes do not address safe practices for cleaning fuel gas piping.
  • NFPA 37 provided no guidance about how to effectively clean new gas piping to gas turbines without creating a fire and explosion hazard and endangering workers.
  • NFPA 850 does not address safe practices for cleaning power plant fuel gas piping.

Recommendations

  1. 2010-01-I-CT-UR1 — Recipient: Occupational Safety and Health Administration (OSHA) — Status: Not specified — Summary: Promulgate regulations that address fuel gas safety for both construction and general industry. At a minimum: prohibit the release of flammable gas to the atmosphere for the purpose of cleaning fuel gas piping; prohibit flammable gas venting or purging indoors; prohibit venting or purging outdoors where fuel gas may form a flammable atmosphere in the vicinity of workers and/or ignition sources; prohibit any work activity in areas where the concentration of flammable gas exceeds a fixed low percentage of the lower explosive limit (LEL) determined by appropriate combustible gas monitoring; require that companies develop flammable gas safety procedures and training that involves contractors, workers, and their representatives in decision-making.
  2. 2010-01-I-CT-UR2 — Recipient: National Fire Protection Association (NFPA) — Status: Not specified — Summary: Enact a Tentative Interim Amendment and permanent changes to the National Fuel Gas Code (NFPA 54/ANSI Z223.1) that address the safe conduct of fuel gas piping cleaning operations. At a minimum: remove the existing NFPA 54 fuel gas piping exemptions for power plants and systems with an operating pressure of 125 pounds per square inch gauge (psig) or more; for cleaning methodology, require the use of inherently safer alternatives such as air blows or pigging with air in lieu of flammable gas.
  3. 2010-01-I-CT-UR3 — Recipient: American Society of Mechanical Engineers (ASME) — Status: Not specified — Summary: Make appropriate changes to the 2012 version of Power Piping, ASME B31.1, to require the use of inherently safer fuel gas piping cleaning methodologies rather than natural gas blows. At a minimum, for the cleaning or flushing methods discussed in B31.1 paragraph 122.10, require the use of inherently safer alternatives such as air blows and pigging with air as the motive force in lieu of flammable gas.
  4. 2010-01-I-CT-UR4 — Recipient: Major Gas Turbine Manufactures - General Electric — Status: Not specified — Summary: Provide to your customers comprehensive technical guidance on inherently safer methods for cleaning fuel gas piping, such as the use of air or pigging with air; comprehensive Cleaning Force Ratio (CFR) guidelines, specifying both the upper and lower limits required to obtain satisfactory cleaning for the fuel gas piping for purposes of the warranties of the turbines; warnings against the use of fuel gas to clean pipes.
  5. 2010-01-I-CT-UR5 — Recipient: Major Gas Turbine Manufactures - Siemens — Status: Not specified — Summary: Provide to your customers comprehensive technical guidance on inherently safer methods for cleaning fuel gas piping, such as the use of air or pigging with air; comprehensive Cleaning Force Ratio (CFR) guidelines, specifying both the upper and lower limits required to obtain satisfactory cleaning for the fuel gas piping for purposes of the warranties of the turbines; warnings against the use of fuel gas to clean pipes.
  6. 2010-01-I-CT-UR6 — Recipient: Major Gas Turbine Manufactures - Solar — Status: Not specified — Summary: Provide to your customers comprehensive technical guidance on inherently safer methods for cleaning fuel gas piping, such as the use of air or pigging with air; comprehensive Cleaning Force Ratio (CFR) guidelines, specifying both the upper and lower limits required to obtain satisfactory cleaning for the fuel gas piping for purposes of the warranties of the turbines; warnings against the use of fuel gas to clean pipes.
  7. 2010-01-I-CT-UR7 — Recipient: Major Gas Turbine Manufactures - Mitsubishi Power Systems — Status: Not specified — Summary: Provide to your customers comprehensive technical guidance on inherently safer methods for cleaning fuel gas piping, such as the use of air or pigging with air; comprehensive Cleaning Force Ratio (CFR) guidelines, specifying both the upper and lower limits required to obtain satisfactory cleaning for the fuel gas piping for purposes of the warranties of the turbines; warnings against the use of fuel gas to clean pipes.
  8. 2010-01-I-CT-UR8 — Recipient: Major Gas Turbine Manufactures - Pratt & Whitney — Status: Not specified — Summary: Provide to your customers comprehensive technical guidance on inherently safer methods for cleaning fuel gas piping, such as the use of air or pigging with air; comprehensive Cleaning Force Ratio (CFR) guidelines, specifying both the upper and lower limits required to obtain satisfactory cleaning for the fuel gas piping for purposes of the warranties of the turbines; warnings against the use of fuel gas to clean pipes.
  9. 2010-01-I-CT-UR9 — Recipient: Major Gas Turbine Manufactures - Rolls-Royce — Status: Not specified — Summary: Provide to your customers comprehensive technical guidance on inherently safer methods for cleaning fuel gas piping, such as the use of air or pigging with air; comprehensive Cleaning Force Ratio (CFR) guidelines, specifying both the upper and lower limits required to obtain satisfactory cleaning for the fuel gas piping for purposes of the warranties of the turbines; warnings against the use of fuel gas to clean pipes.
  10. 2010-01-I-CT-UR10 — Recipient: General Electric — Status: Open- Acceptable Response — Summary: Work with the Electric Power Research Institute to publish technical guidance addressing the safe cleaning of fuel gas piping supplying gas turbines. At minimum: for cleaning methodology, require the use of inherently safer alternatives such as air blows and pigging with air in lieu of flammable gas; provide technical guidance for the safe and effective use of alternative methods for cleaning such as air and pigging with air.
  11. 2010-01-I-CT-UR11 — Recipient: Solar — Status: Closed- Acceptable Action — Summary: Work with the Electric Power Research Institute to publish technical guidance addressing the safe cleaning of fuel gas piping supplying gas turbines. At minimum: for cleaning methodology, require the use of inherently safer alternatives such as air blows and pigging with air in lieu of flammable gas; provide technical guidance for the safe and effective use of alternative methods for cleaning such as air and pigging with air.
  12. 2010-01-I-CT-UR12 — Recipient: Siemens Energy, Inc. — Status: Closed- Acceptable Action — Summary: Work with the Electric Power Research Institute to publish technical guidance addressing the safe cleaning of fuel gas piping supplying gas turbines. At minimum: for cleaning methodology, require the use of inherently safer alternatives such as air blows and pigging with air in lieu of flammable gas; provide technical guidance for the safe and effective use of alternative methods for cleaning such as air and pigging with air.
  13. 2010-01-I-CT-UR13 — Recipient: Mitsubishi Power Systems, Inc. (MPSA) — Status: Closed- Acceptable Action — Summary: Work with the Electric Power Research Institute to publish technical guidance addressing the safe cleaning of fuel gas piping supplying gas turbines. At minimum: for cleaning methodology, require the use of inherently safer alternatives such as air blows and pigging with air in lieu of flammable gas; provide technical guidance for the safe and effective use of alternative methods for cleaning such as air and pigging with air.
  14. 2010-01-I-CT-UR14 — Recipient: Pratt & Whitney Power Systems, Inc. (PWPS) — Status: Closed-Acceptable Action — Summary: Work with the Electric Power Research Institute to publish technical guidance addressing the safe cleaning of fuel gas piping supplying gas turbines. At minimum: for cleaning methodology, require the use of inherently safer alternatives such as air blows and pigging with air in lieu of flammable gas; provide technical guidance for the safe and effective use of alternative methods for cleaning such as air and pigging with air.
  15. 2010-01-I-CT-UR15 — Recipient: Rolls-Royce — Status: Closed – Acceptable Action — Summary: Work with the Electric Power Research Institute to publish technical guidance addressing the safe cleaning of fuel gas piping supplying gas turbines. At minimum: for cleaning methodology, require the use of inherently safer alternatives such as air blows and pigging with air in lieu of flammable gas; provide technical guidance for the safe and effective use of alternative methods for cleaning such as air and pigging with air.
  16. 2010-01-I-CT-UR16 — Recipient: The Governor and Legislature of the State of Connecticut — Status: Closed- Acceptable Action — Summary: Enact legislation applicable to power plants in the state that prohibits the use of flammable gas that is released to the atmosphere to clean fuel gas piping.
  17. 2010-01-I-CT-UR17 — Recipient: The Governor and Legislature of the State of Connecticut — Status: Closed- No Longer Applicable — Summary: Adopt the current version of NFPA 54 as amended pursuant to 2010-01-I-CT-R2.
  18. 2010-01-I-CT-UR18 — Recipient: Electric Power Research Institute (EPRI) — Status: Not specified — Summary: Work with the six turbine manufacturers identified in this document to publish technical guidance addressing the safe cleaning of fuel gas piping supplying gas turbines. At minimum: for cleaning methodology, require the use of inherently safer alternatives such as air blows and pigging with air in lieu of flammable gas; provide comprehensive technical guidance on inherently safer methods for cleaning fuel gas piping, such as the use of air or pigging with air.

Key Engineering Lessons

  • Releasing large volumes of natural gas to the atmosphere for pipe cleaning is inherently unsafe because of the intrinsic fire and explosion hazards.
  • Safer alternatives to natural gas blows exist, including air blows and pigging with air.
  • Vent piping location, orientation, and surrounding congestion affect dispersion and must be technically evaluated before any release.
  • Cleaning procedures should be supported by written procedures, worker review, and hazard-specific safety meetings.
  • Ignition source control must address both outside and inside the work area, including electrical power, welding, and heaters.
  • Cleaning force ratio targets alone are not sufficient unless the overall cleaning method avoids flammable gas release.

Source Notes

  • Priority 1 final report facts were used to resolve conflicts over incident sequence, consequences, and findings.
  • Recommendation status change documents were used only for recommendation status updates and corroborating findings where consistent with the final report.
  • Supporting documents were used only where they provided explicit incident details not contradicted by the final report.
  • Some recommendation IDs in supporting documents contain OCR or formatting inconsistencies; the most authoritative form from the final report was preserved where available.

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