US Chemical Safety and Hazard Investigation Board

The Hazards of Nitrogen Asphyxiation

Introduction

• Nitrogen makes up 78% of the air we Nitrogen makes up 78% of the air we breath; because of this it is often breath; because of this it is often assumed that nitrogen is not hazardous.assumed that nitrogen is not hazardous.

• However, However, nitrogen is safe to breathnitrogen is safe to breath onlyonly if it is mixed with an appropriate amount if it is mixed with an appropriate amount of oxygen. of oxygen.

• Additional nitrogen (lower oxygen) Additional nitrogen (lower oxygen) cannot be detected by the sense of smell.cannot be detected by the sense of smell.

Introduction

• Nitrogen is used commercially as an Nitrogen is used commercially as an inerting agent to keep material free of inerting agent to keep material free of contaminants (including oxygen) that may contaminants (including oxygen) that may corrode equipment, present a fire hazard, corrode equipment, present a fire hazard, or be toxic.or be toxic.

• A lower oxygen concentration (e.g., A lower oxygen concentration (e.g., caused by an increased amount of caused by an increased amount of nitrogen) can have a range of effects on nitrogen) can have a range of effects on the human body and can be fatal if if falls the human body and can be fatal if if falls below 10% below 10%

Effects of Oxygen Deficiency on the Human Body

AAtmospheric tmospheric Oxygen Oxygen

Concentration (%)Concentration (%)Possible ResultsPossible Results

20.920.9 NormalNormal

19.019.0 Some unnoticeable adverse physiological Some unnoticeable adverse physiological effectseffects

16.016.0 Increased pulse and breathing rate, impaired Increased pulse and breathing rate, impaired thinking and attention, reduced coordinationthinking and attention, reduced coordination

14.014.0 Abnormal fatigue upon exertion, emotional Abnormal fatigue upon exertion, emotional upset, faulty coordination, poor judgmentupset, faulty coordination, poor judgment

12.512.5 Very poor judgment and coordination, Very poor judgment and coordination, impaired respiration that may cause impaired respiration that may cause permanent heart damage, nausea, and permanent heart damage, nausea, and vomitingvomiting

<10<10 Inability to move, loss of consciousness, Inability to move, loss of consciousness, convulsions, deathconvulsions, death

Source: Compressed Gas Association, 2001

Statistics on Incidents

CSB reviewed cases of nitrogen asphyxiation CSB reviewed cases of nitrogen asphyxiation that occurred in the US between 1992 and that occurred in the US between 1992 and 2002 and determined the following:2002 and determined the following:

• 85 incidents of nitrogen asphyxiation 85 incidents of nitrogen asphyxiation resulted in 80 deaths and 50 injuries.resulted in 80 deaths and 50 injuries.

• The majority of incidents occurred in The majority of incidents occurred in manufacturing and industrial settings, but manufacturing and industrial settings, but several incidents occurred in other several incidents occurred in other settings including laboratories and medical settings including laboratories and medical facilities.facilities.

Facilities and Areas Where Incidents

Occurred

14%

13%

5%6%

62%

Manufacturing/industry

Trenches, manhole covers (notidentified)

Maintenance activities (notnecessarily at manufacturing sites)

Laboratories

Miscellaneous (including medicalfacilities and transportation)

Statistics on Incidents (cont’d)

• The majority of incidents The majority of incidents occurred in and around occurred in and around confined spaces, though confined spaces, though several incidents occurred several incidents occurred in “open” areas, including in “open” areas, including inside buildings and inside buildings and outdoors near equipment.outdoors near equipment.

• Almost half the incidents Almost half the incidents involved contractors, involved contractors, including construction including construction workers. Contractors workers. Contractors account for over 60% of the account for over 60% of the fatalities.fatalities.

Statistics on Incidents (cont’d)

Causes of the incidents Causes of the incidents included:included:

• Failure to detect an oxygen-Failure to detect an oxygen-deficient atmosphere in and deficient atmosphere in and around confined spaces.around confined spaces.

• Mistakenly using nitrogen instead Mistakenly using nitrogen instead of breathing air. of breathing air.

• Inadequately preparing for rescue. Inadequately preparing for rescue.

Data Sources for Statistics

• Data sources for the CSB review Data sources for the CSB review included regulatory agencies, media included regulatory agencies, media reports, technical publications, and reports, technical publications, and contacts with safety personnel; contacts with safety personnel; however, only those incidents that however, only those incidents that were reported and accessible are were reported and accessible are evaluated. Statistical analysis is based evaluated. Statistical analysis is based on the available, limited information.on the available, limited information.

• Although the summary data reported Although the summary data reported above are not all-inclusive, the above are not all-inclusive, the numbers clearly indicate that nitrogen numbers clearly indicate that nitrogen asphyxiation presents a serious asphyxiation presents a serious hazard in the workplace. hazard in the workplace.

Case Study: Failure to Recognize Asphyxiation Hazards Near Confined

Spaces Three workers were cleaning Three workers were cleaning

filters in a hydrogen purifying filters in a hydrogen purifying tank. tank.

• Tank was purged with nitrogen Tank was purged with nitrogen during cleaning.during cleaning.

• One worker leaned over a One worker leaned over a manway opening in the upper manway opening in the upper portion of the tank.portion of the tank.

• He was found unconscious and He was found unconscious and later died. later died.

Case Study: Failure to Recognize Asphyxiation Hazards Near Confined

Spaces An operator was conducting a flammable An operator was conducting a flammable

gas test on a line connected to a flare gas test on a line connected to a flare in order to issue a hot work permit. in order to issue a hot work permit.

• The operator issued a permit that The operator issued a permit that required an air-supplied respirator.required an air-supplied respirator.

• Two contractors wore respirators to Two contractors wore respirators to remove a valve, but the operator did remove a valve, but the operator did not.not.

• Nitrogen inadvertently entered the Nitrogen inadvertently entered the flare and the operator lost flare and the operator lost consciousness.consciousness.

Case Study: Inadequate Monitoring of Atmosphere

A tank car at a refinery contained A tank car at a refinery contained white mineral oil, and an white mineral oil, and an employee started cleaning it. employee started cleaning it.

• The mineral oil was offloaded by The mineral oil was offloaded by injecting nitrogen gas into the injecting nitrogen gas into the car.car.

• The nitrogen was still present The nitrogen was still present when the employee started to when the employee started to clean the car and he was clean the car and he was asphyxiated.asphyxiated.

Case Study: Corrupt Breathing Air Supply

Two contractors were abrasive blasting Two contractors were abrasive blasting tubes inside a boiler.tubes inside a boiler.

• They wore supplied-air respirators They wore supplied-air respirators connected to compressed air cylinders.connected to compressed air cylinders.

• After the workers failed to respond to After the workers failed to respond to an air horn, they were found an air horn, they were found unconscious. unconscious.

• Follow-up testing of the air supply – Follow-up testing of the air supply – which had been manufactured by which had been manufactured by mixing oxygen and nitrogen - found mixing oxygen and nitrogen - found that it contained less than 5% oxygen.that it contained less than 5% oxygen.

Case Study: Mix-Up Nitrogen and Air, and Improper Rescue

The atmosphere inside a coated tank The atmosphere inside a coated tank was tested and ventilated the day was tested and ventilated the day before work was to be performed before work was to be performed inside.inside.

• A contractor entered the tank to clean it A contractor entered the tank to clean it the next day and collapsed.the next day and collapsed.

• Two plant employees attempted rescue Two plant employees attempted rescue and were overcome. All three workers and were overcome. All three workers died.died.

• The tank had mistakenly been ventilated The tank had mistakenly been ventilated with nitrogen instead of compressed air. with nitrogen instead of compressed air.

Case Study: Mix-up Nitrogen and Air

A contract employee planned to A contract employee planned to use a hammer powered by air to use a hammer powered by air to chip residue from a furnace in chip residue from a furnace in an aluminum foundry.an aluminum foundry.

• He wore an airline respirator. He wore an airline respirator. • Two compressed gas lines were Two compressed gas lines were

available, one was labeled “natural available, one was labeled “natural gas” and one was labeled “air”.gas” and one was labeled “air”.

• Once the respirator was in place, the Once the respirator was in place, the employee was asphyxiated. The “air” employee was asphyxiated. The “air” line actually contained pure line actually contained pure nitrogen.nitrogen.

Case Study: Mix-up Breathing Air Supply in a Medical Facility

A supplier mistakenly delivered A supplier mistakenly delivered a cylinder of nitrogen during a a cylinder of nitrogen during a delivery of oxygen cylinders.delivery of oxygen cylinders.

• The nursing home employee The nursing home employee mistakenly accepted the nitrogen mistakenly accepted the nitrogen tank.tank.

• The cylinder was labeled with a The cylinder was labeled with a nitrogen label partially covering nitrogen label partially covering an oxygen label.an oxygen label.

Case Study: Mix-Up Breathing Air Supply in a Medical Facility

(cont’d)• The tank had nitrogen-The tank had nitrogen-

compatible fittings.compatible fittings.• A maintenance employee A maintenance employee

removed the fittings from an removed the fittings from an empty oxygen cylinder and empty oxygen cylinder and used it as an adapter to used it as an adapter to connect the nitrogen tank to connect the nitrogen tank to the oxygen system.the oxygen system.

• Four patients died and six Four patients died and six were injured. were injured.

Good Practices for Safe Handling of Nitrogen

Implement warning systems and Implement warning systems and continuous atmospheric monitoring continuous atmospheric monitoring of enclosuresof enclosures

• Continuously monitor for oxygen-Continuously monitor for oxygen-deficient, toxic, or explosive deficient, toxic, or explosive atmospheres. atmospheres.

• Employ warning systems including Employ warning systems including flashing lights, alarms, and auto-locking flashing lights, alarms, and auto-locking entryways.entryways.

• Use personnel monitors to indicate low Use personnel monitors to indicate low oxygen concentrations.oxygen concentrations.

• Remember that the atmosphere can Remember that the atmosphere can change over time.change over time.

Good Practices for Safe Handling of Nitrogen

Ensure ventilation with fresh-air Ensure ventilation with fresh-air in confined and enclosed areas.in confined and enclosed areas.

• Maintain continuous forced draft Maintain continuous forced draft ventilation with fresh air before job ventilation with fresh air before job begins and through completion.begins and through completion.

• Ensure that ventilation systems are Ensure that ventilation systems are properly designed, evaluated, and properly designed, evaluated, and maintained.maintained.

• Use warning systems to alert Use warning systems to alert personnel if the system fails.personnel if the system fails.

Good Practices for Safe Handling of Nitrogen

Implement a system for the safe Implement a system for the safe retrieval and rescue of workersretrieval and rescue of workers

• Employees in confined spaces should Employees in confined spaces should wear equipment to facilitate wear equipment to facilitate retrieval, such as a body harness, retrieval, such as a body harness, anklets, or wristlets, and a lifeline.anklets, or wristlets, and a lifeline.

• Standby personnel must be present Standby personnel must be present at all times and have constant at all times and have constant communication with personnel inside.communication with personnel inside.

• Personnel should not attempt rescue Personnel should not attempt rescue unless they are properly trained and unless they are properly trained and equipped. equipped.

Good Practices for Safe Handling of Nitrogen

Ensure the uninterrupted flow Ensure the uninterrupted flow and integrity of breathing airand integrity of breathing air

• Take steps to ensure that supplied air is Take steps to ensure that supplied air is not interrupted. Steps include having not interrupted. Steps include having alternate sources of power for air alternate sources of power for air compressors, inspecting and replacing air compressors, inspecting and replacing air hoses, and restricting traffic in areas with hoses, and restricting traffic in areas with supply hoses.supply hoses.

• Carry escape packs.Carry escape packs.• Ensure the composition of supplied Ensure the composition of supplied

breathing air is correct. Continuously breathing air is correct. Continuously monitor the air supply.monitor the air supply.

Good Practices for Safe Handling of Nitrogen

Prevent inadvertent mix-up Prevent inadvertent mix-up of nitrogen and breathing of nitrogen and breathing airair

• Ensure that personnel understand Ensure that personnel understand the reason for specific unique the reason for specific unique fittings on cylinders of different fittings on cylinders of different compressed gases. Do not compressed gases. Do not fabricate “adapters” to defeat fabricate “adapters” to defeat their purpose.their purpose.

• Ensure that cylinders are clearly Ensure that cylinders are clearly labeled.labeled.

• Use color coding to identify Use color coding to identify systems.systems.

Good Practices for Safe Handling of Nitrogen

Develop and implement training Develop and implement training programs for employees and contract programs for employees and contract personnel, including information on:personnel, including information on:

• Proper use of ventilation, retrieval, air Proper use of ventilation, retrieval, air monitoring, and air supply systems.monitoring, and air supply systems.

• Safe practices for confined space entry and Safe practices for confined space entry and rescue. Precautions to take when working rescue. Precautions to take when working around confined areas.around confined areas.

• Dangers of nitrogen enriched atmosphere Dangers of nitrogen enriched atmosphere and preventing mix-ups between breathing and preventing mix-ups between breathing air and nitrogen.air and nitrogen.

• Implementing good hazard communication.Implementing good hazard communication.

More Information

A safety bulletin and 1-page A safety bulletin and 1-page brochure on the hazards of brochure on the hazards of nitrogen asphyxiation, as well as nitrogen asphyxiation, as well as this presentation, are available this presentation, are available from the US Chemical Safety and from the US Chemical Safety and Hazard Investigation Board. Hazard Investigation Board.

www.csb.govwww.csb.gov

(202)261-7600(202)261-7600