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Removal of Hazardous Material from Piping Systems

Overview

In January 2004, the U.S. Chemical Safety and Hazard Investigation Board (CSB) investigated an explosion and fire at a Huntsman Petrochemical Corporation facility in Port Neches, Texas. During a steam purge for a piping modification that required line opening and hot work, a peroxide/alcohol mixture trapped in a low point along a 900-foot-long, 6-inch process pipe was heated above its thermal decomposition temperature. Plant personnel incorrectly believed a preceding nitrogen gas purge had removed all liquid from the pipe. The trapped mixture decomposed, overpressurized the pipe, and ruptured it. The venting flammable vapor ignited, causing a flash fire that injured two employees and damaged nearby equipment.

Incident Snapshot

Field Value
Facility / Company Huntsman Petrochemical Corporation
Location Port Neches, Texas
Incident Date 01/13/2004
Investigation Status The CSB issued this safety bulletin on July 15, 2004. This Safety Bulletin identifies specific tasks that facilities should include in all work activities involving piping or equipment opening to ensure the complete removal of hazardous material. In addition, guidance is provided on implementing generic (plant-wide) procedures for nonroutine work activities.
Accident Type Explosion and fire
Final Report Release Date 07/15/2004

What Happened

  • In January 2004, the U.S. Chemical Safety and Hazard Investigation Board (CSB) investigated an explosion and fire at a Huntsman Petrochemical Corporation facility in Port Neches, Texas.
  • During a steam purge for a piping modification that required line opening and hot work, a peroxide/alcohol mixture was heated above its thermal decomposition temperature.
  • The mixture was trapped in a low point along a 900-foot-long, 6-inch process pipe.
  • Plant personnel incorrectly believed that a nitrogen gas purge preceding the steam purge had removed all liquid from the pipe.
  • An unknown quantity of a thermally reactive peroxide/alcohol mixture remained in an unidentified low-point trap in the pipe.
  • As the steam heated the trapped peroxide, it exothermically decomposed and overpressurized the pipe, causing it to rupture.
  • The venting flammable vapor then ignited, resulting in a flash fire that burned two employees and significantly damaged nearby equipment.
  • The automatic deluge system and the fire brigade suppressed the fire.

Facility and Process Context

  • Chemical and refinery facility personnel open piping and equipment to perform routine maintenance, add/replace components, or modify pipe routing.
  • The pipe routing contained a low-point segment almost 300 feet long, with a volume in excess of 350 gallons.
  • The pipe was routed more than 20 feet above-ground in an overhead pipe rack that obscured the long, shallow low-point section.
  • This was the first time hot work had been specified for this line.
  • As in most large chemical manufacturing facilities, many miles of piping were routed throughout overhead pipe racks.

Consequences

  • Fatalities: None reported.
  • Injuries: Two employees were seriously injured; two employees were burned.
  • Environmental Release: None reported.
  • Facility Damage: Significantly damaged nearby equipment; pipe/valve rupture; floor stanchion and piping tangled in damaged overhead electrical conduits; additional damage to equipment in the area.
  • Operational Impact: The fire was suppressed by the automatic deluge system and the fire brigade.

Key Findings

Immediate Causes

  • Incomplete Removal of Hazardous Mixture
  • Unsafe Heating of Thermally Sensitive Chemicals

Contributing Factors

  • The procedural steps for the nitrogen gas purge were ineffective in removing all of the hazardous mixture from the pipe.
  • The modification work order for the infrequently used startup line required hot work on the pipe; it included a nitrogen purge before opening the line, similar to the normal line clearing procedure.
  • Operators were unaware that the nitrogen gas purging, required by the operating procedure, was ineffective in removing all of the peroxide/alcohol mixture in the low point.
  • The pipe routing contained a low-point segment almost 300 feet long, with a volume in excess of 350 gallons.
  • The pipe was routed more than 20 feet above-ground in an overhead pipe rack that obscured the long, shallow low-point section.
  • The low-point piping segment and two available drains were shown on the as-built piping isometrics, but the low point was split onto separate sheets, making it difficult to recognize the liquid trap.
  • The piping modification involved only one of the isometric drawings.
  • Using the generic steam purging procedure on the peroxide/alcohol pipe created an unanticipated hazard.
  • The steam temperature exceeded 380ºF, which is significantly above the decomposition temperature of the peroxide.
  • The high-temperature steam flowed through the piping system for nearly 1.5 hours, and the trapped peroxide began to decompose.
  • Pressure buildup ultimately caused a valve gasket to fail and release flammable vapor.
  • The pipe upstream of the leaking valve burst, releasing additional flammable liquid and vapor, further spreading the fire.
  • Complex pipe routing and equipment configurations often contain low points that trap hazardous material.
  • Purging with inert gas or steam does not necessarily remove trapped liquid.
  • The revised procedure failed to address the importance of identifying low points in the piping.
  • The revised procedure failed to require the use of low-point drains to remove trapped hazardous liquids.
  • The revised inert gas purging procedure was applied to process pipes containing thermally unstable liquids without adequately considering the hazards if these liquids remained in the pipe during the steam purge.

Organizational and Systemic Factors

  • Huntsman operating and maintenance procedures highlighted the hazards of incomplete removal of toxic, flammable, or reactive chemicals from pipes and equipment.
  • To reduce waste volume, Huntsman revised the procedures to substitute inert gas purging for water flushing.
  • A comprehensive review of the as-built drawings, combined with a walkdown of the entire peroxide/alcohol transfer pipe—if required in the management of change (MOC) process—would have likely identified the low-point trap.
  • After the incident, Huntsman conducted a comprehensive walkdown of all peroxide piping and identified additional low-point traps.
  • An MOC work order was implemented to eliminate each trap.

Failed Safeguards or Barrier Breakdowns

  • Plant personnel incorrectly believed that a nitrogen gas purge preceding the steam purge had removed all liquid from the pipe.
  • The procedural steps for the nitrogen gas purge were ineffective in removing all of the hazardous mixture from the pipe.
  • The revised procedure failed to address the importance of identifying low points in the piping.
  • The revised procedure failed to require the use of low-point drains to remove trapped hazardous liquids.
  • The as-built piping isometrics did not make the low-point trap easy to recognize because the low point was split onto separate sheets.
  • The generic steam purging procedure did not account for thermally unstable liquids remaining in the pipe during the steam purge.

Recommendations

  • No formal CSB recommendations with IDs, recipients, or statuses were included in the provided Safety Bulletin text.

Key Engineering Lessons

  • Safe work practices dictate the removal or mechanical isolation of hazardous material from piping and equipment (e.g., using valves or blind flanges) before commencing work.
  • Opening chemical process piping and equipment can be extremely hazardous and should never be considered routine work.
  • Perform a complete walkdown of all piping and components between the isolation devices and update as-built drawings as necessary.
  • Use as-built drawings of the affected piping to identify all branch connections, isolation valves, low-point drains, and high-point vents.
  • Prepare a specific written procedure for removing, flushing, and purging hazardous material from the system, and consider the consequences if flushing liquid remains in the system after the work is complete.
  • Review planned steps against unit-specific hazards.
  • Update unit-specific procedures as necessary to address unique characteristics of the activity, especially when modifications are involved.
  • If a modification activity includes the use of generic safety procedures, clearly identify applicable constraints, including additional inspection steps to verify removal of all energy sources, including thermally reactive chemicals.

Source Notes

  • All fields contain only information explicitly stated in the provided document text.
  • The document is a Safety Bulletin and does not include formal CSB recommendations with IDs, recipients, or statuses in the provided text.

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