Safety

Bulletin

U.S. Chemical Safety and Hazard Investigation Board

HAZARDS OF NITROGEN ASPHYXIATION

Introduction

E very year people are killed by breathing “air” that contains too little

 oxygen. Because 78 percent of the air we breathe is nitrogen gas,

many people assume that nitrogen is not harmful. However, nitrogen is

safe to breathe only when mixed with the appropriate amount of oxygen.

These two gases cannot be detected by the sense of smell. A nitrogenenriched environment, which depletes oxygen, can be detected only with

special instruments. If the concentration of nitrogen is too high (and

oxygen too low), the body becomes oxygen deprived and asphyxiation

occurs.

1 In 1998, the U.S. Chemical Safety Board

(CSB) investigated a nitrogen

asphyxiation incident that occurred in

Hahnville, Louisiana. As part of that

investigation, CSB reviewed the

prevalence of asphyxiation incidents.

No. 2003-10-B | June 2003

This Safety Bulletin is published to bring additional

attention to the continuing

hazards of nitrogen asphyxiation.1

 Nitrogen is widely used commercially. It is often used to

keep material free of contaminants (such as oxygen) that

may corrode equipment,

present a fire hazard, or be

toxic.

 Nitrogen asphyxiation hazards

in industry resulted in 80 deaths

from 1992 to 2002. These

incidents occurred in a variety

of facilities, including industrial

plants, laboratories, and

medical facilities; almost half

involved contractors.

 Good practices and awareness

of hazards minimize the risk

of nitrogen asphyxiation

(Figure 1).

Many incidents reviewed by CSB

were caused by inadequate

knowledge of the hazard or

Commercial

Uses of Nitrogen

One of the most important

commercial uses of nitrogen is as

an inerting agent to improve

safety. Nitrogen is inert under

most conditions (i.e., it does not

react with or affect other material).

It is often used to keep material

free of contaminants, including

oxygen—which can corrode

equipment or present a fire and

explosion hazard when in contact

with flammable liquids or

combustible solids. In such cases,

a flow of nitrogen is maintained in

a vessel to keep oxygen out.

Nitrogen is also used to purge air

from equipment prior to

introducing material, or to purge

flammable or toxic material prior

to opening equipment for

maintenance.

In industrial and commercial

settings where a nitrogen-enriched

environment may present a

hazard, such as when using

supplied air or working in or

around spaces that are confined,

N Figure 1. Sign warning of

nitrogen hazard.

inadvertent use of nitrogen rather

than breathing-air delivery

systems.

This bulletin focuses only on the

hazard of asphyxiation, though

nitrogen also presents cryogenic

and high-pressure hazards.
2

precautions must be taken to

ensure that sufficient oxygen is

provided to personnel.

CSB Safety Bulletins offer advisory

information on good practices for

managing chemical process hazards.

Case studies provide supporting

information. Safety Bulletins differ

from CSB Investigation Reports in

that they do not comprehensively

review all the causes of an incident.

U.S. Chemical Safety and Hazard

Investigation Board

Office of Investigations and Safety

Programs

2175 K Street NW, Suite 400

Washington, DC 20037-1848

202-261-7600

www.chemsafety.gov

serious and immediate effects,

including unconsciousness after

only one or two breaths. The

exposed person has no warning

and cannot sense that the oxygen

level is too low.

The Occupational Safety and

Health Administration (OSHA)

requires employers to maintain

workplace oxygen at levels

between 19.5 and 23.5 percent. As

shown in the table on page 3, the

human body is adversely affected

by lower concentrations.

As the oxygen concentration falls

below 16 percent, the brain sends

commands to the breathing control

center, causing the victim to

resuscitated, he or she risks

cardiac arrest.

N Nitrogen . . . presents a

hazard when it displaces

oxygen.

2 Data sources for the CSB review include

regulatory agencies, media reports,

technical publications, and contacts with

safety personnel; however, only those

incidents that were reported and accessible

are represented. Although the summary

data reported above are not all-inclusive,

the numbers clearly indicate that nitrogen

asphyxiation presents a serious hazard in

the workplace. Statistical analysis is based

on available, limited information.

N Nitrogen is safe to

breathe only when mixed

with the appropriate

amount of oxygen.

Effects of

OxygenDeficient

Atmosphere

Nitrogen is not a “poison” in the

traditional sense. It presents a

hazard when it displaces oxygen,

making the atmosphere hazardous

to humans. Breathing an oxygendeficient atmosphere can have

N In industrial and

commercial settings

where a nitrogenenriched environment

may present a hazard,

. . . precautions must be

taken to ensure that

there is sufficient oxygen

in the atmosphere.

breathe faster and deeper. As the

oxygen level continues to

decrease, full recovery is less

certain. An atmosphere of only 4

to 6 percent oxygen causes the

victim to fall into a coma in less

than 40 seconds. Oxygen must be

administered within minutes to

offer a chance of survival. Even

when a victim is rescued and

Statistics on

Nitrogen

Asphyxiation

From reported data for the United

States, CSB identified 85 nitrogen

asphyxiation incidents that

occurred in the workplace

between 1992 and 2002. In these

incidents, 80 people were killed

and 50 were injured. 2

Profile of Affected

Industries and Activities

Of the 85 incidents reported, 62

percent occurred in chemical

plants and refineries, food

processing and storage facilities,

metal and manufacturing

operations, and other industrial,

maritime, and manufacturing

sites, including nuclear plants.

Approximately 13 percent of the

incidents involved maintenance
3

identified as being in manufacturing facilities—account for

about 14 percent of the incidents.

The remainder of the incidents

occurred in laboratories and

miscellaneous industries, such as

medical and transportation.

The data show that employees and

contractors alike are victims of

asphyxiation. Of the 85 incidents

reviewed, 42 involved contractors,

including construction workers;

N CSB identified 85

nitrogen asphyxiation

incidents that occurred in

the workplace between

1992 and 2002 . . . 80

people were killed and 50

were injured.

N . . . 130 workplace

fatalities and injuries

occurred from breathing

nitrogen-enriched air.

Over 60 percent of these

victims were working in

or next to a confined

space.

3

 “Next to a confined space” means that a

person’s breathing zone is affected by the

atmosphere emanating from the space.

The person may be standing in the

immediate area but not actually in the

space.

4

According to OSHA, a confined space can

be entered to perform work, has limited

means of egress, and is not designed for

continuous employee occupancy. A

“permit-required confined space” includes

a space that contains or has the potential to

contain a serious safety or health hazard,

such as a hazardous atmosphere.

activities, such as railcar and tank

truck cleaning, painting,

maintenance, and repair. These

incidents are categorized as

“maintenance” because incident

reports do not include enough

information on the type of

industrial setting; they could have

occurred at manufacturing sites,

which would increase the 62

percent estimate above.

Likewise, trenches and

manholes—not specifically

these 42 incidents account for over

60 percent of the fatalities.

Causal Information

From the CSB data, a combined

total of 130 workplace fatalities

and injuries occurred from

breathing nitrogen-enriched air.

Over 60 percent of these victims

were working in or next to a

confined space.3,4

One characteristic of a confined

space is its capability to contain an

atmosphere that may be totally

different from outside air.

Confined spaces in manufacturing

sites typically include equipment

such as reactors, vessels, tanks,

and boilers. Other such spaces are

railcars, trenches, and areas

accessible by manholes.

N Of the 85 incidents

reviewed, 42 involved

contractors, including

construction workers;

these 42 incidents

account for over 60

percent of the fatalities.

Effects of Oxygen Deficiency on the Human Body

20.9 Normal

19.0 Some unnoticeable adverse physiological effects

16.0 Increased pulse and breathing rate, impaired

thinking and attention, reduced coordination

14.0 Abnormal fatigue upon exertion, emotional upset,

faulty coordination, poor judgment

12.5 Very poor judgment and coordination, impaired

respiration that may cause permanent heart

damage, nausea, and vomiting

<10 Inability to move, loss of consciousness,

convulsions, death

Atmospheric

Oxygen

Concentration (%) Possible Results

SOURCE: Compressed Gas Association, 2001.
4

flush equipment prior to entry. In

either situation, inadequate

knowledge of the hazard and

failure to detect additional

nitrogen resulted in a fatal

concentration of gas.

N When fatalities and injuries

occurred in “open areas”

. . . the hazard of

asphyxiation was not

expected and personnel

were typically caught off

guard.

N In one incident, a worker

mistakenly used nitrogen

instead of air to purge a

confined space . . . In

another case, workers

inadvertently connected

the hose for their

breathing-air respirator

to a pure nitrogen line.

The data provide examples of

workers inadvertently using

nitrogen instead of air because of

interchangeable couplings on lines

and poor or nonexistent labeling.

In one incident, a worker

mistakenly used nitrogen instead

of air to purge a confined space.

An inert atmosphere was

unexpected and undetected. One

worker was killed, and a colleague

also died while attempting rescue.

In another case, workers

inadvertently connected the hose

for their breathing-air respirator to

a pure nitrogen line.

Failure to Detect OxygenDeficient Atmosphere

Failure to detect an oxygendeficient (nitrogen-enriched)

atmosphere was a significant

factor in several incidents.

In the data evaluated for this

study, 67 of the 85 incidents

involved circumstances where

personnel were in or around a

confined area—such as a railcar,

room, process vessel, or tank

(Figure 2)—and nitrogen was

initially present in high levels or

later collected in the area. These

incidents accounted for 62

fatalities and 33 injuries. In each

of the 67 incidents, personnel

failed to detect elevated levels of

nitrogen and take appropriate

precautions.

When fatalities and injuries

occurred in “open areas”

(including areas with ventilation,

laboratories, buildings, and

outside in the vicinity of

equipment), the

hazard of

asphyxiation

was not

expected and

personnel were

typically caught

off guard. In

some cases,

personnel

unknowingly

created a

nitrogenenriched

atmosphere by

mistakenly

using nitrogen

instead of air to

Mix-Up of Nitrogen and

Breathing Air

Confusing nitrogen gas with air

and problems with breathing-air

delivery systems accounted for 12

of the 85 incidents, and approximately 20 percent of fatalities.

Fatalities and Injuries

During Attempted Rescue

One of the most difficult issues

concerning hazardous atmosphere

emergencies is the human instinct

to aid someone in distress.

Approximately 10 percent of

fatalities from the CSB data were

due to attempts to rescue injured

persons in confined spaces.

N Figure 2. Confined area.
5

Asphyxiation Hazards

Outside Industry and

Effect on General Public

Asphyxiation hazards may also be

present outside industry,

especially among people who use

breathing air, such as firefighters,

divers, and medical patients.

Statistics on these types of

incidents are difficult to collect

and are not included in this

bulletin, though one such case is

summarized below.

The victim used a lift to access the

external area of the upper tank,

which was fitted with a manway.

As he leaned into the tank

opening, his coworkers noticed

that he was not responding to

their communication. They found

the victim unconscious, and he

later died as a result of oxygen

deficiency.

Employee Overcome While

Testing Atmosphere

An operator was conducting a

flammable gas test on a tower

feedline that discharged into a

low-pressure flare gas header.

The test was required for a hot

work permit to take flash photos.

The chief operator issued a work

permit that required a suppliedair respirator. Two contractor

pipefitters wore respirators and

removed the safety valve. The

operator, however, wore no

respiratory protection. After

climbing the scaffold, he was

overcome by nitrogen gas from

the open flare line before he could

complete atmospheric sampling.

The operator backed away,

turned, and slumped to his knees.

He was disoriented and briefly

lost consciousness. An investigation concluded that the incident

was due to elevated levels of

nitrogen gas that had

inadvertently entered the flare

system.

Inadequate Monitoring of

Atmosphere

Contractor Asphyxiated Inside

Tank Car

White mineral oil in a tank car at

an oil refinery was offloaded by

injecting nitrogen gas into the car.

An employee of a railcar cleaning

company was asphyxiated while

cleaning the nitrogen-filled tank

car.

Corrupt Breathing Air

Supply

Two Laborers/Painting

Contractors Asphyxiated

Two painting contractors were

abrasive-blasting tubes inside a

boiler at a chemical plant. They

each wore supplied-air respirators

connected to a 12-pack cluster of

compressed air cylinders. Another

subcontractor monitored the work

outside the confined space.

Work proceeded normally

throughout the night shift;

however, at 3:00 am, the attendant

got no response after repeatedly

sounding the air horn. When

another contractor employee was

sent into the boiler to assess the

situation, he found the two men

lying on opposite ends of the

scaffolding.

When the plant health, safety, and

environmental department tested

the compressed air 12-pack, they

found that it contained less than 5

percent oxygen. The “air” had

been manufactured with too low a

N Approximately 10

percent of fatalities from

the CSB data were due

to attempts to rescue

injured persons in

confined spaces.

Selected Case

Studies

Failure to Recognize

Asphyxiation Hazards

Near Confined Spaces

Employee Dies After Partially

Entering a Nitrogen-Purged

Tank

Two coworkers and the victim

were cleaning filters in a hydrogen

purifying tank. The tank was

partly purged with nitrogen to

remove internal dust particles.
6

concentration of oxygen. (Note:

This fatal incident prompted

OSHA to issue a safety alert on the

batch of breathing air.)

Mix-Ups Between

Nitrogen and Air

Three Employees Asphyxiated in

Coating Tank

The atmosphere inside a coating

tank was tested and ventilated the

day before work was to be

performed. On the following day,

a contractor entered the tank to

clean it and collapsed. Two plant

employees entered to attempt

rescue, but they were also

overcome.

The tank had been ventilated with

what was thought to be compressed air but was actually

nitrogen. The atmosphere was not

tested prior to beginning work.

All three men were asphyxiated.

Employee Killed by

Overexposure to Pure Nitrogen

A contractor planned to use an airpowered hammer to chip residue

from a furnace in an aluminum

foundry. He wore an airline

respirator. Of two compressed gas

lines with fittings, one was labeled

“natural gas” and the other had an

old paper tag attached with “air”

handwritten on it. However, this

line actually contained pure

nitrogen.

A splitter diverted one part of the

gas stream to the air hammer and

the other part to the airline respirator. Once the respirator was

in place, the worker breathed

pure nitrogen and was

asphyxiated.

Four Killed and Six Injured in

Nursing Home

A nursing home routinely

ordered large pure oxygen

compressed gas cylinders for

residents with respiratory system

diseases. The supplier mistakenly

delivered one cylinder of pure

nitrogen with three cylinders of

oxygen; a nursing home

maintenance employee

mistakenly accepted the nitrogen

tank.

Another maintenance employee

took this cylinder, which had a

nitrogen label partially covering

an oxygen label, to connect it to

the oxygen supply system. The

tank was fitted with nitrogencompatible couplings. The

employee removed a fitting from

an empty oxygen cylinder and

used it as an adapter to connect

the nitrogen tank to the oxygen

system. Four deaths and six

injuries occurred as a result of

pure nitrogen being delivered to

the patients.

Good Practices

for Safe

Handling of

Nitrogen

Implement Warning

Systems and Continuous

Atmospheric Monitoring

of Enclosures

The atmosphere in a confined

space or small enclosed area may

be unfit for breathing prior to

entry, or it may change over time,

depending on the type of

equipment or work being

performed. Recognizing this

hazard, good practice calls for

continuous monitoring of a

confined space to detect oxygendeficient, toxic, or explosive

atmospheres. The entire confined

space should be monitored—not

just the entry portal.

Warning and protection systems

include flashing lights, audible

alarms, and auto-locking

entryways to prevent access. Such

devices, if properly installed and

N The atmosphere in a

confined space or small

enclosed area may be

unfit for breathing prior

to entry, or it may

change over time . . .
7

Personnel should be trained on

how to properly respond and

evacuate in the event of failure of

the system.

Implement System for

Safe Rescue of Workers

Rescue may be necessary in the

event of continuous monitoring,

ventilation failure, or another

emergency condition. The ability

to immediately retrieve

immobilized workers is a critical

component of confined space entry

preplanning.

or legs. The attendant and rescue

personnel should be available at

all times. Rescuers must have an

effective system to communicate

with personnel inside enclosures.

No one should enter a dangerous

atmosphere without proper

personal protective equipment.

The last measure of defense

requires personnel to actually

enter the confined area to retrieve

the victim. This approach should

be used only when personnel are

appropriately trained, have

donned rescue equipment, and

have dependable breathing air.

Approximately 10 percent of

fatalities from the survey data

occurred to personnel attempting

rescue. These deaths could have

been prevented if a reliable

retrieval system was in place.

Such a system would also prevent

many entry worker fatalities

because it provides for quickly

removing the worker from a

dangerous atmosphere to a safe

one.

Ensure Uninterrupted

Flow and Integrity of

Breathing Air

Breathing air must be supplied

when workers enter environments

where oxygen is or may become

deficient. Workers may use either

a self-contained breathing

apparatus (SCBA) or an airline

respirator, which consists of a long

hose connecting a breathing air

supply to the respirator or hood.

Because a worker using an airline

respirator does not control the

maintained, warn workers of

hazardous atmospheres. Personal

monitors can measure oxygen

concentration and give an audible

or vibration alarm for low oxygen

concentrations.

N It is essential to maintain

continuous forced draft

fresh-air ventilation

before the job begins

through to completion.

N Good practice calls for

continuous monitoring

of a confined space to

detect oxygendeficient, toxic, or

explosive atmospheres.

One method is to attach a body

harness and lifeline to personnel

entering confined areas. This

procedure also benefits potential

rescuers because they do not have

to enter the confined area to

retrieve the victim. However,

when a worker enters a pipeline,

some furnaces, ducts, or other

narrow-diameter confined spaces,

pulling on a line attached to a

body harness may cause the

person to bunch up and become

stuck inside.

Depending on the situation,

wristlets or anklets attached to a

lifeline and a retrieval mechanism

allow the confined space attendant

to pull the person out by the arms

Ensure Ventilation With

Fresh Air

Because the atmosphere of a

confined space or small/enclosed

area often changes during the

course of work, it is essential to

maintain continuous forced draft

fresh-air ventilation before the job

begins through to completion.

Areas with the potential to contain

elevated levels of nitrogen gas

should be continuously ventilated

prior to and during the course of

the job.

Ventilation is also required in

rooms and chambers into which

nitrogen may leak or vent. In a

few of the study cases, people who

were simply working close to the

nitrogen-containing confined

space, room, or enclosure were

asphyxiated.

Systems must be in place to

properly design, evaluate, and

maintain ventilation systems. A

warning system will alert workers

of a dangerous atmosphere.
8

N Breathing air must be

supplied when workers

enter environments

where oxygen is or may

become deficient.

and dedicated to breathing-air

systems. The compressor should

have a moisture trap, an oil trap,

and a carbon monoxide sensor and

alarm. When breathing air is

manufactured by mixing nitrogen

and oxygen, the pressure of the

cylinders during filling must be

known to ensure that the correct

amounts are mixed. The final

product must be tested to ensure

its integrity.

Prevent Inadvertent MixUp of Nitrogen and

Breathing Air

To prevent interchanging compressed nitrogen with compressed

industrial grade air or compressed

breathing-quality air, specific

fittings should be used for each

cylinder. Cylinders for nitrogen,

industrial grade air, and

breathing-quality air have distinct,

incompatible fittings that cannot

be cross-connected.

N Personnel should

understand that the

fittings are intended to

be incompatible to

ensure safety.

source of supply, air may

suddenly or inadvertently be

interrupted. For example, a power

failure may stop an air

compressor, the air supply may

simply run out, or the supply hose

may become twisted or obstructed

(e.g., by a vehicle). When supplied

air is used, facility management

systems must protect against

interruption of airflow and

provide alternate sources of power

for the compressors.

A comprehensive management

system includes the following:

 Continuous monitoring of air

supply.

 Routine inspection and

replacement of supplied-air

hoses.

 Restriction of vehicular traffic in

the area of supply hoses.

When using supplied air, a worker

should carry a small backup

cylinder (escape pack)—attached

to a different supplied-air

system—with enough breathing

air to last 5 to 10 minutes.

Breathing air is manufactured

either by purifying and

compressing air or by mixing

nitrogen and oxygen to the

appropriate ratio. A breathing-air

compressor and its hoses should

be specifically manufactured for

fittings are additional reminders of

which gas is contained inside.

Color coding also helps to identify

systems.

Develop and Implement

Comprehensive Training

Programs

The good practices for safe

handling of nitrogen, described

above, are effective only if

personnel are trained on the

importance of the following:

 Use of ventilation systems,

retrieval systems, and

atmospheric monitoring

equipment—both how to use

them and how to determine

when they are not working

properly.

 Dangers of nitrogen-enriched

atmospheres and the systems to

Personnel should understand that

the fittings are intended to be

incompatible to ensure safety.

Cylinders should be clearly

labeled; typical cylinders are

shown in Figure 3. Labels on

piping systems, compressors, and

N Figure 3. Compressed

gas cylinders.
9

References and

Additional

Information

American National Standards

Institute (ANSI)/American

Society of Safety Engineers

(ASSE), 2003. Safety

Requirements for Confined Spaces,

Z117.1-2003.

ANSI/ASSE, 2003. Criteria for

Accepted Practices in Safety,

Health, and Environmental

Training, Z490.1-2001.

ANSI, 2002. Standards on Signage

and Labeling, Z535 Series.

Compressed Gas Association, Inc.,

2002. Standard for Compressed

Gas Cylinder Valve Outlet and

Inlet Connections, V-1, 10th

edition.

Compressed Gas Association, Inc.,

2001. Safety Bulletin, OxygenDeficient Atmospheres, SB-2, 4th

edition.

Compressed Gas Association, Inc.,

1999. Handbook of Compressed

Gases, 4th edition, Kluwer

Academic Publishers.

Federal Aviation Administration

(FAA), 2003. NASA Physiology

Training, www.faa.gov/avr/

cmo/coa/PH-TR.html.

Finkel, Martin H., 2000. Guidelines

for Hot Work in Confined Spaces;

Recommended Practices for

Industrial Hygienists and Safety

Professionals, ASSE.

Harris, Michael K., Lindsay E.

Booher, and Stephanie Carter,

1996. Field Guidelines for

Temporary Ventilation of Confined

Spaces, American Industrial

Hygiene Association (AIHA).

Kletz, Trevor, 1995. What Went

Wrong? Case Histories of Process

Plant Disasters, Gulf Publishing

Company.

Institution of Chemical Engineers

(IChemE), 2003. Accident Data

Base, she@ichme.org.uk.

Martin, Lawrence, 1997. “Effects

of Gas Pressure at Depth:

Nitrogen Narcosis, CO and CO2

Toxicity, Oxygen Toxicity, and

‘Shallow-Water’ Blackout,”

Scuba Diving Explained,

Physiology and Medical Aspects of

Scuba Diving, Best Publishing

Company.

McManus, Neil, 1999. Safety and

Health in Confined Spaces, Lewis

Publishers/CRC Press.

National Institute for Occupational

Safety and Health (NIOSH),

2002. “State FACE Investigations of Fatal ConfinedSpace Incidents,” Traumatic

Occupational Injury,

www.cdc.gov/niosh/face, OctNov 2002.

Occupational Safety and Health

Administration (OSHA), 2003.

Safety and Health Topics:

Confined Spaces, www.osha.gov/

SLTC/confinedspaces/

index.html.

N Contractors as well as

employees should be

trained.

prevent interchanging breathing

air and nitrogen.

 Implementing good hazard

communication, which includes

safe handling of air and

nitrogen delivery systems.

 Mandatory safety practices and

procedures for entry into

confined spaces, such as

permits, providing an attendant,

monitoring, ventilating, rescue,

and contractor oversight.

 Precautions when working

around equipment that may

contain elevated levels of

nitrogen.

 The reason for special fittings on

compressed gas cylinders.

 Proper use of air supply

equipment.

Training should cover new and

revised procedures for confined

space entry, and establish

measurements for employee

proficiency. Contractors as well as

employees should be trained.
10

The U.S. Chemical Safety and Hazard Investigation Board (CSB) is an independent Federal agency whose mission is to

ensure the safety of workers, the public, and the environment by investigating and preventing chemical incidents. CSB

is a scientific investigative organization; it is not an enforcement or regulatory body. Established by the Clean Air Act

Amendments of 1990, CSB is responsible for determining the root and contributing causes of accidents, issuing safety

recommendations, studying chemical safety issues, and evaluating the effectiveness of other government agencies

involved in chemical safety.

No part of the conclusions, findings, or recommendations of CSB relating to any chemical incident may be admitted as

evidence or used in any action or suit for damages arising out of any matter mentioned in an investigation report (see

42 U.S.C. § 7412(r)(6)(G)). CSB makes public its actions and decisions through investigation reports, summary

reports, safety bulletins, safety recommendations, case studies, incident digests, special technical publications, and

statistical reviews. More information about CSB may be found at www.chemsafety.gov.

Salus Populi Est Lex Suprema

People’s Safety is the Highest Law

CSB investigation reports may be purchased from:

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

(800) 553-NTIS or (703) 487-4600

Email: info@ntis.fedworld.gov

For international orders, see:

www.ntis.gov/support/cooperat.htm.

Information about available publications may be

obtained by contacting:

U.S. Chemical Safety and Hazard Investigation Board

Office of Prevention, Outreach, and Policy

2175 K Street NW, Suite 400

Washington, DC 20037-1848

(202) 261-7600

OSHA, 2002. Accident Investigation

Summary Index Page,

www.osha.gov, Oct-Nov 2002.

OSHA, 1994. “Permit-Required

Confined Spaces,” Federal

Register, 29 CFR 1910.146, May

1994.

Rekus, John F., 1994. Complete

Confined Spaces Handbook, Lewis

Publishers/CRC Press.

Safety Engineering, 2002. Daily

Incident Alert Archives,

www.safteng.net, Oct-Nov 2002.

The Bureau of National Affairs,

Inc. (BNA), 1998. Occupational

Safety and Health Reporter, Vol.

27, No. 46, April 22, 1998.

BNA, 1996. Occupational Safety and

Health Reporter, Vol. 25, No. 47,

May 1, 1996.

U.S. Air Force, 2003. Hypoxia,

www.batnet.com/mfwright/

hypoxia.html.

U.S. Chemical Safety and Hazard

Investigation Board (USCSB),

2002. Incident Data Base,

www.csb.gov, Oct-Nov 2002.