Skip to content

Hazards of Nitrogen Asphyxiation

Overview

CSB safety bulletin on nitrogen asphyxiation hazards. The bulletin states that nitrogen is safe to breathe only when mixed with the appropriate amount of oxygen, that a nitrogen-enriched environment can be detected only with special instruments, and that oxygen deficiency can be fatal. The bulletin reviews 85 workplace nitrogen asphyxiation incidents from 1992 to 2002, resulting in 80 deaths and 50 injuries, with many incidents occurring in or around confined spaces and involving contractors.

Incident Snapshot

Field Value
Facility / Company Not provided
Location Not provided
Incident Date 06/25/2003
Investigation Status The CSB issued this safety bulletin on June 25, 2003.
Accident Type Confined Space / Asphyxiation
Final Report Release Date 06/25/2003

What Happened

CSB reviewed 85 nitrogen asphyxiation incidents in the workplace between 1992 and 2002.

Many incidents occurred in and around confined spaces, and some involved mistaken use of nitrogen instead of breathing air.

Selected case studies included a worker found unconscious after leaning over a manway opening in a nitrogen-purged tank, an operator overcome after nitrogen inadvertently entered a flare line, a worker asphyxiated when nitrogen remained in a tank car, contractors overcome while using supplied-air respirators, a contractor asphyxiated after a tank had been ventilated with nitrogen instead of compressed air, an employee asphyxiated when an air line actually contained pure nitrogen, and a nursing home incident in which a nitrogen cylinder was mistakenly connected to an oxygen system.

In the nursing home case, a supplier mistakenly delivered a cylinder of nitrogen during a delivery of oxygen cylinders, the nitrogen tank was accepted, and a maintenance employee used fittings from an empty oxygen cylinder to connect the nitrogen tank to the oxygen system, resulting in four patient deaths and six injuries.

Facility and Process Context

  • Manufacturing and industrial settings
  • Confined spaces and areas around confined spaces
  • Laboratories
  • Medical facilities and nursing homes
  • Hydrogen purifying tank
  • Flare line / low-pressure flare gas header
  • Refinery tank car
  • Boiler
  • Coated tank
  • Aluminum foundry furnace
  • Oxygen system in a nursing home

Consequences

  • Fatalities:
  • 80 deaths in the CSB review.
  • Additional case-study fatalities include one worker, three workers, and four patients.
  • Injuries:
  • 50 injuries in the CSB review.
  • Four patients were injured in the medical facility case.
  • Environmental release:
  • Not reported.
  • Facility damage:
  • Not reported.
  • Operational impact:
  • Not reported.

Key Findings

Immediate Causes

  • Failure to detect an oxygen-deficient atmosphere in and around confined spaces.
  • Mistakenly using nitrogen instead of breathing air.
  • Inadequately preparing for rescue.

Contributing Factors

  • Nitrogen cannot be detected by the sense of smell.
  • The atmosphere can change over time.
  • Nitrogen-enriched atmospheres deplete oxygen.
  • The tank had mistakenly been ventilated with nitrogen instead of compressed air.
  • The "air" line actually contained pure nitrogen.
  • The air supply contained less than 5% oxygen.
  • The cylinder was labeled with a nitrogen label partially covering an oxygen label.
  • A maintenance employee removed the fittings from an empty oxygen cylinder and used it as an adapter to connect the nitrogen tank to the oxygen system.
  • Interchangeable couplings on lines and poor or nonexistent labeling contributed to mix-ups between nitrogen and breathing air.
  • Inadequate monitoring of atmosphere and failure to test the atmosphere prior to beginning work contributed to incidents.

Organizational and Systemic Factors

  • Data sources for the CSB review were limited to reported and accessible incidents, so the summary is not all-inclusive.
  • Training programs should cover new and revised procedures for confined space entry.
  • Contractors as well as employees should be trained.
  • Facility management systems must protect against interruption of airflow and provide alternate sources of power for compressors.
  • Systems must be in place to properly design, evaluate, and maintain ventilation systems.

Failed Safeguards or Barrier Breakdowns

  • Failure to detect an oxygen-deficient atmosphere in and around confined spaces.
  • Inadequately preparing for rescue.
  • Special instruments were not used to detect a nitrogen-enriched environment.
  • Continuous monitoring of a confined space was not performed.
  • The entire confined space was not monitored, not just the entry portal.
  • Warning and protection systems were not properly installed and maintained.
  • A reliable retrieval system was not in place.
  • Proper personal protective equipment was not used.
  • Dependable breathing air was not available.
  • Continuous forced draft fresh-air ventilation was not maintained before the job began through to completion.
  • Areas with the potential to contain elevated levels of nitrogen gas were not continuously ventilated prior to and during the course of the job.
  • Specific fittings were not used for each cylinder.
  • Cylinders were cross-connected.
  • Cylinders were not clearly labeled.
  • Air supply was interrupted.
  • The compressed air 12-pack contained less than 5 percent oxygen.

Recommendations

  1. Recommendation ID: Not provided. Recipient: Not provided. Status: Not provided. Implement warning systems and continuous atmospheric monitoring of enclosures.
  2. Recommendation ID: Not provided. Recipient: Not provided. Status: Not provided. Ensure ventilation with fresh air in confined and enclosed areas.
  3. Recommendation ID: Not provided. Recipient: Not provided. Status: Not provided. Implement a system for the safe retrieval and rescue of workers.
  4. Recommendation ID: Not provided. Recipient: Not provided. Status: Not provided. Ensure the uninterrupted flow and integrity of breathing air.
  5. Recommendation ID: Not provided. Recipient: Not provided. Status: Not provided. Prevent inadvertent mix-up of nitrogen and breathing air.
  6. Recommendation ID: Not provided. Recipient: Not provided. Status: Not provided. Develop and implement training programs for employees and contract personnel, including information on proper use of ventilation, retrieval, air monitoring, and air supply systems; safe practices for confined space entry and rescue; precautions to take when working around confined areas; dangers of nitrogen enriched atmosphere and preventing mix-ups between breathing air and nitrogen; and implementing good hazard communication.

Key Engineering Lessons

  • A nitrogen-enriched environment can be detected only with special instruments; smell is not a reliable warning method.
  • Atmospheres in and around confined spaces must be continuously monitored because conditions can change over time.
  • Fresh-air ventilation must be maintained before work begins and through completion where nitrogen accumulation is possible.
  • Breathing-air systems must be protected from interruption and verified for correct oxygen content.
  • Unique fittings, clear labels, and color coding are needed to prevent cross-connection of nitrogen and breathing air systems.
  • Safe rescue provisions, including retrieval equipment and trained standby personnel, are necessary because rescue attempts can also become fatalities.

Source Notes

  • Consolidated from CSB final report and safety bulletin extracts with source_priority 1 taking precedence over supporting document text.
  • The incident dataset reflects a bulletin summarizing multiple nitrogen asphyxiation cases and statistics rather than a single event at a named facility.
  • No facility/company name or specific location was provided in the source extracts.
  • Where multiple case studies were described, event_sequence and consequences were summarized without adding external facts.

Similar Incidents

Incidents sharing the same equipment, root causes, or hazard types.

Same Equipment

Same Root Cause

← View in Knowledge Graph