NATURAL GAS EXPLOSION — INDOOR PURGING OF GAS PIPING INTO BUILDING
ConAgra Slim Jim Plant Natural Gas Explosion
ConAgra Foods, Inc.
📍 Garner, NC
Incident: June 9, 2009  •  CSB Report: February 4, 2010
4
Fatalities
Natural Gas (Purged into Occupied Building from Gas Distribution Piping)
Chemical Involved
4
CSB Recommendations
📋 Incident Summary

On June 9, 2009, four workers were fatally injured and dozens of others were injured when a natural gas explosion occurred at the ConAgra Foods Slim Jim manufacturing facility in Garner, North Carolina. The explosion occurred during maintenance on a natural gas distribution line inside the building -- specifically, during the process of purging the gas piping to remove air before returning it to service.

CSB investigation found that gas piping was being purged by releasing natural gas into the interior of the building, rather than venting it safely outdoors. The purged gas accumulated to an explosive concentration inside the occupied facility and ignited. The applicable natural gas code at the time (NFPA 54/National Fuel Gas Code) did not explicitly prohibit indoor purging of gas piping -- an omission the CSB found to be a critical regulatory gap.

The CSB issued 4 urgent recommendations to the National Fire Protection Association (NFPA), American Gas Association (AGA), and International Code Council (ICC) to immediately prohibit indoor purging of fuel gas piping and require outdoor venting in revised editions of the National Fuel Gas Code and International Fuel Gas Code. All four recommendations were implemented. The case remains one of the clearest examples of a fatal incident resulting from a gap in a national gas code.

🔎 Key Findings
Finding 01
Gas Piping Purged Indoors -- Flammable Gas Released Into Occupied Building
Workers purging a natural gas distribution line to remove air before returning it to service released the purged natural gas directly into the interior of the ConAgra Slim Jim plant -- an occupied building with workers present and ignition sources throughout.
Finding 02
Natural Gas Accumulated to Explosive Concentration and Ignited
The natural gas released during indoor purging accumulated to a flammable concentration inside the building. When the accumulated gas encountered an ignition source, it exploded, causing 4 fatalities and dozens of injuries.
Finding 03
National Fuel Gas Code Did Not Prohibit Indoor Purging
The applicable national standard (NFPA 54 / National Fuel Gas Code) did not explicitly require that purged fuel gas be vented outdoors. This regulatory gap permitted a practice that could release explosive quantities of gas into occupied buildings.
Finding 04
CSB Issued Urgent Recommendations -- Code Changes Implemented
The CSB issued urgent recommendations to NFPA, AGA, and ICC to prohibit indoor purging and require outdoor venting. All four recommendations were implemented in revised editions of the National Fuel Gas Code and International Fuel Gas Code -- directly preventing this scenario from recurring at facilities nationwide.
Finding 05
Indoor Gas Purging Is an Industry-Wide Hazard Practice
Investigation revealed that the practice of purging fuel gas piping into occupied buildings was not limited to ConAgra -- it was a common field practice reflecting the absence of a code prohibition. The code change addressed a nationwide hazard, not just a site-specific deficiency.
🔍 Root Causes
1
Absence of Code Prohibition on Indoor Gas Purging Allowed Dangerous Practice to Persist
The National Fuel Gas Code did not explicitly prohibit the release of purged gas inside occupied buildings, leaving a regulatory gap that allowed a practice with catastrophic explosion potential to be performed routinely by maintenance workers across the country who were following standard industry practice.
2
Gas Maintenance Procedures Did Not Require Outdoor Venting of Purged Gas
The maintenance procedure used at ConAgra for gas piping purging did not require -- and may have implicitly permitted -- indoor release of purged gas. Without a clear procedure requiring outdoor venting, workers followed common field practice, which proved fatal.
3
Workers Were Not Aware That Indoor Gas Purging Creates an Explosion Hazard
The workers performing the gas piping purge were not aware that accumulation of natural gas inside an occupied building could rapidly reach explosive concentrations and result in a catastrophic explosion with an ordinary ignition source.
☑ CSB Recommendations
→ National Fire Protection Association and American Gas Association
Immediately amend the National Fuel Gas Code (NFPA 54/ANSI Z223.1) to require that purged fuel gases be directly vented to a safe location outdoors, away from personnel and ignition sources; if outdoor venting is not possible, require documented risk evaluation and hazard control plan with combustible gas monitoring.
→ ICC International Fuel Gas Code Committee and International Code Council
Incorporate the revised gas purging provisions of the National Fuel Gas Code into the International Fuel Gas Code, prohibiting the release of purged fuel gas into occupied buildings and requiring outdoor venting.
→ National Fire Protection Association and American Gas Association
Train personnel on the problems of odor fade and odor fatigue and warn against relying on odor alone for detecting fuel gas releases during maintenance.
→ ICC International Fuel Gas Code Committee and International Code Council
Ensure that the revised purging provisions address all commercial, institutional, and industrial applications where gas piping maintenance may require purging to atmosphere.
💡 Lessons Learned
Natural gas is not safe to release inside a building, even briefly, during maintenance. Gas released for purging accumulates in low areas, follows air currents, and can reach explosive concentration before workers can smell it (due to odor fade or odor fatigue of the odorant). Outdoor venting of purged gas is the only acceptable practice.
The absence of a code prohibition is not the same as permission. Before the ConAgra explosion, the National Fuel Gas Code did not explicitly prohibit indoor purging. Workers followed standard field practice -- a practice that the code's silence had implicitly sanctioned. Facilities must evaluate the safety of common maintenance practices even when no code prohibition exists.
Odor fatigue and odor fade mean you cannot rely on smell to detect dangerous concentrations of natural gas during maintenance. Workers may be exposed to enough odorant early in a task that their sense of smell is fatigued before the gas concentration reaches explosive levels. Continuous combustible gas monitoring is required when purging gas in enclosed spaces.
The ConAgra case demonstrates the value of CSB urgent recommendations. The CSB's four recommendations resulted in code changes that prohibit indoor gas purging nationwide -- preventing this specific scenario from recurring at the thousands of facilities that maintain gas piping. One fatal incident, properly investigated, changed a national code.
Workers performing fuel gas system maintenance should receive specific training on the explosive hazard of natural gas and the code requirement to vent purged gas outdoors. The fact that indoor purging was a common field practice before 2009 means many workers may have received training that reflects outdated and now-prohibited practices.
SOP: Operating ProceduresTRN: TrainingHOW: Hot Work / Safe Work
🔨 Safety Meeting Toolbox Talk
►When gas piping at your facility is purged before or after maintenance, where does the purged gas go? Is it specifically required to be vented outdoors, away from building openings and ignition sources?
►Do your gas piping maintenance procedures reflect the current National Fuel Gas Code and International Fuel Gas Code requirement to prohibit indoor purging? Have procedures been updated since 2010?
►Do workers performing gas system maintenance use continuous combustible gas monitoring equipment? Do they understand that odor alone is not a reliable indicator of gas concentration?
►What ignition sources are present in the areas where gas piping maintenance is performed? Have those sources been identified, and is a plan in place to control them during gas work?
►Has your facility reviewed gas maintenance practices against post-2009 code requirements? If workers were trained before 2010, they may have received training that reflects practices now prohibited by the updated codes.
Immediate Action Items
✓Pull your current gas piping maintenance procedures and verify they explicitly require that purged fuel gas be vented outdoors, away from building openings and ignition sources, consistent with current NFPA 54 and International Fuel Gas Code requirements.
✓Require combustible gas monitoring during all gas piping maintenance activities in enclosed spaces -- do not permit reliance on odor detection as the primary means of detecting gas accumulation.
✓Identify and control all ignition sources in areas where gas piping maintenance will be performed before maintenance begins -- including electrical equipment, pilot lights, and mechanical sparks.
✓Confirm that all workers and contractors who perform gas piping maintenance have received training specifically covering the prohibition on indoor purging and the outdoor venting requirements of current codes.
✓Review the training records for gas system maintenance personnel and update training materials to reflect post-2009 code requirements if the materials predate the ConAgra code changes.
🔗 PSM Failures Behind This Incident

This incident traced to breakdowns across 3 PSM elements (SOP · TRN · HOW). 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.
Supporting documents in our library →
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 →
Hot Work Permits
Unauthorized or poorly controlled ignition sources near flammable atmospheres are entirely preventable. A rigorous hot work permit system with pre-job atmospheric testing closes this pathway.
Supporting documents in our library →
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