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Union Carbide Corp. Nitrogen Asphyxiation Incident

Overview

On March 27, 1998, two workers at Union Carbide Corporation’s Taft/Star Manufacturing Plant in Hahnville, Louisiana, were overcome by nitrogen gas while performing a black light inspection at an open end of a 48-inch-wide horizontal pipe. One Union Carbide worker was killed and an independent contractor was seriously injured due to nitrogen asphyxiation. The incident occurred during a turnaround in the plant’s Taft Oxide I Unit, where nitrogen was being used to purge process equipment.

Incident Snapshot

Field Value
Facility / Company Union Carbide Corporation
Location Hahnville, LA
Incident Date 03/27/1998
Investigation Status The final summary report on this investigation was approved on February 23, 1999.
Accident Type Confined Space / Asphyxiation
Final Report Release Date 02/23/1999

What Happened

  • The 48-inch pipe was open because chemical-processing equipment had been shut down and opened for major maintenance.
  • Nitrogen was being injected into the process equipment primarily to protect new catalyst in reactors from exposure to moisture.
  • The nitrogen was also flowing through some of the piping systems connected to the reactors.
  • The nitrogen was venting from one side of the open pipe where it had formerly been connected to an oxygen feed mixer.
  • No warning sign was posted on the pipe opening identifying it as a confined space or warning that the pipe contained potentially hazardous nitrogen.
  • The two workers had placed a sheet of black plastic over the end of the pipe to provide shade to make it easier to conduct the black light test during daylight.
  • While working just outside the pipe opening and inside of the black plastic sheet, the two workers were overcome by nitrogen.
  • The evening before the incident, Worker A directed Operations Technicians to add the nitrogen to the piping because the catalyst had been changed.
  • Because nitrogen would retard rust formation in the piping connected to the reactors, two valves were opened to allow the flow of nitrogen into the process piping.
  • On the day of the incident, Workers A and B performed a black light inspection and cleaning of the two flange surfaces on the open 48-inch pipe, beginning with the south flange.
  • The black plastic sheet was fastened over the pipe flange because there was a strong breeze that day.
  • The inspection and cleaning of the south pipe flange began at approximately 10:45 am and was completed at about 11:35 am.
  • There was no incident because the nitrogen was not venting through the south pipe opening.
  • Next, the workers and the contractors placed a plastic sheet in the same fashion on the north pipe flange while Workers A and B conducted an inspection and cleaning.
  • Because this part of the pipe was being purged with nitrogen, it contained a high level of nitrogen.
  • The temporary plastic enclosure trapped a high concentration of the nitrogen, which continued to vent out of the north pipe.
  • Contractors, who were on the other side of the black plastic sheet, reported talking with Workers A and B.
  • The last communication with Workers A and B took place just after noon.
  • At approximately 12:20 pm, a contractor noticed blood on one of the worker’s hands when he looked through a gap in the plastic sheet.
  • He alerted his foreman.
  • The foreman called to the two workers behind the sheet and, getting no reply, removed the sheet.
  • Worker B was found in front of the pipe, unconscious and slumped over with his head lying inside the open pipe.
  • Worker A was found seated beside the pipe opening, dazed and leaning against the side of the pipe.
  • The plant emergency response team arrived and removed the two men from the Unit while administering cardiopulmonary resuscitation to Worker B.
  • The two workers were transported by ambulance to St. Charles Parish Hospital.
  • Worker B was dead on arrival.
  • Worker A was admitted to the hospital in critical condition and given oxygen therapy over the next several days.
  • He was released after five days in the hospital.

Facility and Process Context

  • The plant, which produces chemicals for industry, is located about 30 miles west of New Orleans and employs approximately 1,130 people.
  • The incident occurred in the plant’s Taft Oxide I Unit.
  • The Unit primarily produces ethylene oxide, ethylene glycol, and glycol ethers.
  • The Unit uses ethylene and methane as feed gases to produce ethylene oxide.
  • Ethylene and methane are mixed with oxygen and then put in contact with a catalyst located in the reactors.
  • A scrubber removes the product while carbon dioxide gas is also removed.
  • The incident occurred at the fifth level of the structure, approximately 60 feet above the ground.
  • At the time of the incident, the Unit had been in a turnaround status for about six weeks.
  • Worker A was retained as an independent contractor and was in charge of daily operations in the reaction area during the turnaround.
  • Worker A had retired from Union Carbide after 32 years of service, primarily at the plant.
  • Worker B was a Union Carbide employee who had 23 years of service at the plant.
  • Worker B was a Maintenance Skilled Operations Team Technician in the Unit.
  • Worker B was under the general direction of Worker A at the time of the incident.

Consequences

  • Fatalities: 1
  • Injuries: 1
  • Environmental Release: Not specified
  • Facility Damage: Not specified
  • Operational Impact: The Unit had been in a turnaround status for about six weeks.

Key Findings

Immediate Causes

  • Nitrogen and confined space hazard warnings were inadequate.
  • Personnel were unable to detect hazardous levels of nitrogen because this gas cannot be detected by human senses.
  • The men were asphyxiated by nitrogen.
  • The plastic sheet created a dangerous enclosure where nitrogen gas could accumulate, displacing oxygen and causing asphyxiation.

Contributing Factors

  • The temporary plastic enclosure trapped a high concentration of the nitrogen.
  • The open pipe was an unrecognized secondary hazard in the oxygen feed mixer cleaning activity.
  • There was no evaluation of the impact of the catalyst change activity and nitrogen purge on the seemingly unrelated oxygen feed mixer cleaning activity.
  • The plant’s safety program did not adequately address the control of hazards associated with the creation of temporary enclosures around chemical plant equipment.
  • Temporary enclosures that had an easy means of exit were generally not covered by the safety requirements of the plant’s confined space entry policy.
  • No signs were posted at the pipe opening to warn workers and contractors that it was a confined space or that it contained nitrogen.
  • Worker A probably did not realize that nitrogen was venting from the pipe even though the evening before he had directed that nitrogen be injected into the piping system.
  • He may have not remembered that nitrogen was in the pipe because the nitrogen was injected at a distant location, 150 feet and several stories in elevation away from the site of the incident.
  • The workers were not aware that they were being exposed to dangerous levels of nitrogen.
  • High concentrations of nitrogen are dangerous because personnel may not recognize physical or mental symptoms resulting from over-exposure.
  • The two workers involved in the incident were unable to recognize that they were in trouble.
  • They did not try to leave the hazardous work area even though there was an easy means of escape.
  • Contractors were located nearby, but the two workers did not ask for help.
  • Inadequate confined-space warnings and entry procedures.
  • Temporary enclosures like the one in this case were not generally covered by the plant’s confined space procedures.
  • No permit was issued prior to the workers’ entry into the enclosure.
  • No precautions were taken to protect the men from the risk of asphyxiation.
  • Operators did not evaluate the risks caused by the nitrogen purge to the workers downstream.
  • Hazards at the open pipe end were not recognized.
  • The open pipe end itself presented a hazard.
  • Humans cannot detect excess levels of nitrogen because the gas is invisible, odorless, and tasteless.

Organizational and Systemic Factors

  • Prior to the incident, the plant’s safety program did not adequately address the control of hazards associated with the creation of temporary enclosures around chemical plant equipment.
  • Management should have performed this type of evaluation when it planned to inject nitrogen into the 48-inch pipe and out of the north end of the pipe.
  • Management personnel said it was unnecessary to clean the flanges because the oxygen feed mixer had been cleaned and an enriched oxygen atmosphere would not contact the flanges.
  • Management did not expect the specific job of a black light inspection to be performed.
  • There were other workers in the area who needed to be protected from the potential nitrogen hazard.
  • The plant had a confined space entry program and a chemical safety-training program. Nonetheless, one very experienced worker died and another was seriously injured because these workers were not aware that they were being exposed to dangerous levels of nitrogen.
  • Although the Union Carbide plant did have procedures for entering confined spaces, CSB found that these procedures did not generally cover temporary enclosures like the one in this case.
  • After the accident, managers said they did not know that the workers were going to perform a black light inspection of the pipe, which led to the creation of a temporary enclosure.

Failed Safeguards or Barrier Breakdowns

  • No warning sign was posted on the pipe opening identifying it as a confined space or warning that the pipe contained potentially hazardous nitrogen.
  • The plant’s safety program did not adequately address the control of hazards associated with the creation of temporary enclosures around chemical plant equipment.
  • Temporary enclosures that had an easy means of exit were generally not covered by the safety requirements of the plant’s confined space entry policy.
  • There was no evaluation of the impact of the catalyst change activity and nitrogen purge on the seemingly unrelated oxygen feed mixer cleaning activity.
  • Recognition of the nitrogen hazard could have identified the need to post a nitrogen warning sign at the pipe opening where the incident took place.
  • Personnel were not aware of the hazard of the nitrogen flowing out of the open pipe that they were working on.
  • The workers were not aware that they were being exposed to dangerous levels of nitrogen.
  • Inadequate confined-space warnings.
  • Entry procedures.
  • No permit was issued prior to the workers’ entry into the enclosure.
  • No precautions were taken to protect the men from the risk of asphyxiation.
  • Operators did not evaluate the risks caused by the nitrogen purge to the workers downstream.
  • Hazards at the open pipe end were not recognized.
  • Warning signs at the pipe opening were not posted.
  • The gas was not odorized.

Recommendations

  1. 98-05-I-LA-R1 | Recipient: Union Carbide Taft Plant | Status: Not specified | Post signs containing the warning “Danger, Confined Space: Do Not Enter Without Authorization” or similar wording at potential entryways when tanks, vessels, pipes, or other similar chemical industry equipment are opened. When nitrogen is added to a confined space, post an additional sign that warns personnel of the potential nitrogen hazard.
  2. 98-05-I-LA-R2 | Recipient: Union Carbide Taft Plant | Status: Not specified | Ensure that the plant safety program addresses the control of hazards created by erecting temporary enclosures around equipment that may trap a dangerous atmosphere in the enclosure if the equipment leaks or vents hazardous material.
  3. 98-05-I-LA-R3 | Recipient: National Institute for Occupational Safety and Health | Status: Not specified | Conduct a study concerning the appropriateness and feasibility of odorizing nitrogen in order to warn personnel of the presence of nitrogen when it is used in confined spaces.
  4. 98-05-I-LA-R4 | Recipient: Occupational Safety and Health Administration | Status: Not specified | Issue a safety alert that addresses the hazards and provides safety guidelines for the use of temporary enclosures that are erected around equipment containing hazardous substances.
  5. 98-05-I-LA-R5 | Recipient: Center for Chemical Process Safety | Status: Not specified | Communicate the findings of this report to your membership.
  6. 98-05-I-LA-R6 | Recipient: Compressed Gas Association | Status: Not specified | Communicate the findings of this report to your membership.

Key Engineering Lessons

  • Temporary enclosures around opened process equipment can trap hazardous atmospheres if the equipment leaks or vents hazardous material.
  • A black plastic sheet used for work convenience can create a dangerous enclosure when placed over an opening connected to a nitrogen purge.
  • Open pipe ends and downstream work areas must be evaluated for hazards created by upstream purge or maintenance activities.
  • Warning signs at opened tanks, vessels, pipes, or similar equipment are needed when a confined space or nitrogen hazard may be present.
  • Nitrogen used in confined spaces is especially hazardous because it is invisible, odorless, tasteless, and cannot be detected by human senses.

Source Notes

  • Priority 1 final report used as primary authority; supporting document used only to supplement where consistent.
  • Conflicting or less specific wording from lower-priority source was not used when the final report provided clearer terminology.
  • All facts were taken only from the provided source extracts; no external information was added.

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