Disclaimer: These guidelines were developed under contract using generally accepted secondary sources. The protocol used by the contractor for surveying these data sources was developed by the National Institute for Occupational Safety and Health (NIOSH), the Occupational Safety and Health Administration (OSHA), and the Department of Energy (DOE). The information contained in these guidelines is intended for reference purposes only. None of the agencies have conducted a comprehensive check of the information and data contained in these sources. It provides a summary of information about chemicals that workers may be exposed to in their workplaces. The secondary sources used for supplements 111 and 1V were published before 1992 and 1993, respectively, and for the remainder of the guidelines the secondary sources used were published before September 1996. This information may be superseded by new developments in the field of industrial hygiene. Therefore readers are advised to determine whether new information is available.
OCCUPATIONAL SAFETY AND HEALTH GUIDELINE FOR NITROUS OXIDE
INTRODUCTION
This guideline summarizes pertinent information about nitrous oxide for
workers and employers as well as for physicians, industrial hygienists, and
other occupational safety and health professionals who may need such
information to conduct effective occupational safety and health programs.
Recommendations may be superseded by new developments in these fields;
readers are therefore advised to regard these recommendations as general
guidelines and to determine whether new information is available.
SUBSTANCE IDENTIFICATION
* Formula
N(2)O
* Structure
(For Structure, see paper copy)
* Synonyms
Dinitrogen monoxide, factitious air, hyponitrous acid anhydride,
laughing gas, nitrogen oxide
* Identifiers
1. CAS No.: 10024-97-2
2. RTECS No.: QX1350000
3. DOT UN: 1070 14 (compressed); 2201 23 (refrigerated liquid)
4. DOT label: Nonflammable gas, oxidizer (nitrous oxide, compressed);
nonflammable gas (nitrous oxide, refrigerated liquid)
* Appearance and odor
Nitrous oxide is a colorless gas at room temperature with a slightly
sweet odor and taste.
CHEMICAL AND PHYSICAL PROPERTIES
* Physical data
1. Molecular weight: 44.02
2. Boiling point (at 760 mm Hg): -88.5 degrees C (-127.3 degrees F)
3. Specific gravity (air = 1): 1.97 at 25 degrees C (77 degrees F)
4. Vapor density: 1.53
5. Melting point: -91 degrees C (-132 degrees F)
6. Vapor pressure: 760 mm Hg at 88.5 degrees C (191.3 degrees F)
7. Solubility: Slightly soluble in water; soluble in alcohol, ether,
oils, and sulfuric acid .
8. Evaporation rate: Data not available.
* Reactivity
1. Conditions contributing to instability: Nitrous oxide can form an
explosive mixture with air.
2. Incompatibilities: Contact of nitrous oxide with aluminum, boron,
hydrazine, lithium hydride, phenyllithium, phosphine, sodium, tungsten
carbide, hydrogen, hydrogen sulfide, organic peroxides, ammonia, or carbon
monoxide may cause violent reactions to occur.
3. Hazardous decomposition products: Toxic gases (such as carbon monoxide
and oxides of nitrogen) may be released in a fire involving nitrous oxide.
4. Special precautions: None reported.
* Flammability
Nitrous oxide is a non-flammable gas at room temperature.
The National Fire Protection Association has not assigned a flammability
rating to nitrous oxide.
1. Flash point: Not applicable.
2. Autoignition temperature: Not applicable.
3. Flammable limits in air: Not applicable.
4. Extinguishant: For small fires use dry chemical or carbon dioxide. Use
water spray, fog, or standard foam to fight large fires involving nitrous
oxide.
Fires involving nitrous oxide should be fought upwind from the
maximum distance possible. Keep unnecessary people away; isolate the hazard
area and deny entry. Isolate the area for 1/2 mile in all directions if a
tank, rail car, or tank truck is involved in the fire. For a massive fire in
a cargo area, use unmanned hose holders or monitor nozzles; if this is
impossible, withdraw from the area and let the fire burn. Emergency
personnel should stay out of low areas and ventilate closed spaces before
entering. Vapors are an explosion hazard indoors, outdoors, or in sewers.
Containers of nitrous oxide may explode in the heat of the fire and should be
moved from the fire area if it is possible to do so safely. If this is not
possible, cool fire-exposed containers from the sides with water until well
after the fire is out. Stay away from the ends of containers. Firefighters
should wear a full set of protective clothing and self-contained breathing
apparatus when fighting fires involving nitrous oxide.
EXPOSURE LIMITS
* OSHA PEL
The Occupational Safety and Health Administration (OSHA) does not
currently regulate nitrous oxide.
* NIOSH REL
The National Institute for Occupational Safety and Health (NIOSH)
has established a recommended exposure limit (REL) for nitrous oxide of 25
parts per million (ppm) parts of air (45 milligrams per cubic meter
(mg/m(3))) as a time-weighted average (TWA) for the duration of the exposure
[NIOSH 1992].
* ACGIH TLV
The American Conference of Governmental Industrial Hygienists
(ACGIH) has assigned nitrous oxide a threshold limit value (TLV) of 50 ppm
(90 mg/m(3)) as a TWA for a normal 8-hour workday and a 40-hour workweek
[ACGIH 1994, p. 28].
* Rationale for Limits
The NIOSH limit is based on the risk of reproductive system effects
and decreases in audiovisual performance [NIOSH 1992].
The ACGIH limit is based on the risk of reproductive, hematological,
and nervous system effects [ACGIH 1991, p. 1137].
HEALTH HAZARD INFORMATION
* Routes of Exposure
Exposure to nitrous oxide occurs through inhalation.
* Summary of toxicology
1. Effects on Animals: Nitrous oxide has central nervous system,
teratogenic, bone marrow, and liver effects in animals [ACGIH 1991]. Rats
exposed to an 80 percent concentration for 2 or more days showed signs of
bone marrow toxicity [ACGIH 1991]. However, rats exposed to a 1 percent
concentration of nitrous oxide for periods ranging from 7 days to 6 months
showed no bone marrow effects [ACGIH 1991]. Exposure to nitrous oxide also
causes neurotoxic (spinal cord lesions, demyelination, peripheral neuropathy)
and hepatotoxic (focal inflammatory lesions) effects in experimental animals
[ACGIH 1991]. In one study, pregnant rats were exposed to 50 percent nitrous
oxide for 24 hours/day starting on day 8 of gestation and continuing for 1,
2, 4, or 6 days; dose-related embryolethal and teratogenic effects occurred
among the offspring. The most common effects were embryonic death,
resorption, and abnormalities of the ribs and vertebrae [Rom 1992]. Nitrous
oxide was negative in three carcinogenicity assays in mice and rats exposed
to concentrations as high as 400,000 ppm for 4 hours/day, 5 days/week for 78
weeks [ACGIH 1991]. The results of mutagenicity assays involving nitrous
oxide were negative [ACGIH 1991].
2. Effects on Humans: Nitrous oxide is an asphyxiant at high
concentrations. At lower concentrations, exposure causes central nervous
system, cardiovascular, hepatic, hematopoietic, and reproductive effects in
humans [Hathaway et al. 1991]. At a concentration of 50 to 67 percent
(500,000 to 670,000 ppm) nitrous oxide is used to induce anesthesia in humans
[Rom 1992]. Patients exposed to a 50:50 mixture of nitrous oxide:oxygen for
prolonged periods to induce continuous sedation developed bone marrow
depression and granulocytopenia [Hathaway et al. 1991; ACGIH 1991]. Although
most patients recover, several deaths from aplastic anemia have been reported
[Hathaway et al. 1991]. Neurotoxic effects occur after acute exposure to
concentrations of 80,000 to 200,000 ppm and above; effects include slowed
reaction times and performance decrements [Hathaway et al. 1991]. Long-term
occupational exposure (dentists, dental assistants) has been associated with
numbness, difficulty in concentrating, paresthesias, and impairment of
equilibrium [Hathaway et al. 1991; ACGIH 1991]. In one study, exposure to 50
ppm nitrous oxide was associated with a decrement in audiovisual performance,
but this result has not been duplicated in other studies [ACGIH 1991].
Epidemiological studies, primarily of operating room personnel, have shown
increased risks of spontaneous abortion, premature delivery, and involuntary
infertility among these occupationally exposed populations [ACGIH 1991;
Hathaway et al. 1991].
* Signs and symptoms of exposure
1. Acute exposure: The signs and symptoms of acute exposure to nitrous
oxide include dizziness, difficult breathing, headache, nausea, fatigue, and
irritability. Acute exposure to nitrous oxide concentrations of 400,000 to
800,000 ppm may cause loss of consciousness [Sittig 1991].
2. Chronic exposure: The signs or symptoms of chronic overexposure to
nitrous oxide may include tingling, numbness, difficulty in concentrating,
interference with gait, and reproductive effects.
EMERGENCY MEDICAL PROCEDURES
* Emergency medical procedures: [NIOSH to supply]
3. Rescue: Remove an incapacitated worker from further exposure and
implement appropriate emergency procedures (e.g., those listed on the
Material Safety Data Sheet required by OSHA's Hazard Communication Standard
[29 CFR 1910.1200]). All workers should be familiar with emergency
procedures, the location and proper use of emergency equipment, and methods
of protecting themselves during rescue operations.
EXPOSURE SOURCES AND CONTROL METHODS
The following operations may involve nitrous oxide and lead to worker
exposures to this substance:
* The manufacture and transportation of nitrous oxide * Use as an
anesthetic gas * Use as a propellant (foaming agent) in whipped creams *
Use as a leak detecting agent on natural gas pipelines * Use as an
oxidant for the production of organic compounds
* Use in rocket fuel formulations * Use in the manufacture of nitrates
from alkali metals
Methods that are effective in controlling worker exposures to nitrous oxide,
depending on the feasibility of implementation, are as follows:
* Process enclosure * Local exhaust ventilation * General dilution
ventilation * Personal protective equipment
Workers responding to a release or potential release of a hazardous
substance must be protected as required by paragraph (q) of OSHA's Hazardous
Waste Operations and Emergency Response Standard [29 CFR 1910.120].
Good sources of information about control methods are as follows:
1. ACGIH [1992]. Industrial ventilation--a manual of recommended
practice. 21st ed. Cincinnati, OH: American Conference of Governmental
Industrial Hygienists.
2. Burton DJ [1986]. Industrial ventilation--a self study companion.
Cincinnati, OH: American Conference of Governmental Industrial Hygienists.
3. Alden JL, Kane JM [1982]. Design of industrial ventilation systems.
New York, NY: Industrial Press, Inc.
4. Wadden RA, Scheff PA [1987]. Engineering design for control of
workplace hazards. New York, NY: McGraw-Hill.
5. Plog BA [1988]. Fundamentals of industrial hygiene. Chicago, IL:
National Safety Council.
MEDICAL SURVEILLANCE
OSHA is currently developing requirements for medical surveillance. When
these requirements are promulgated, readers should refer to them for
additional information and to determine whether employers whose employees are
exposed to nitrous oxide are required to implement medical surveillance
procedures.
Medical Screening:
Workers who may be exposed to chemical hazards should be monitored in a
systematic program of medical surveillance that is intended to prevent
occupational injury and disease. The program should include education of
employers and workers about work-related hazards, early detection of adverse
health effects, and referral of workers for diagnosis and treatment. The
occurrence of disease or other work-related adverse health effects should
prompt immediate evaluation of primary preventive measures (e.g., industrial
hygiene monitoring, engineering controls, and personal protective equipment).
A medical surveillance program is intended to supplement, not replace, such
measures. To detect and control work-related health effects, medical
evaluations should be performed (1) before job placement, (2) periodically
during the term of employment, and (3) at the time of job transfer or
termination.
* Preplacement medical evaluation
Before a worker is placed in a job with a potential for exposure to
nitrous oxide, a licensed health care professional should evaluate and
document the worker's baseline health status with thorough medical,
environmental, and occupational histories, a physical examination, and
physiologic and laboratory tests appropriate for the anticipated occupational
risks. These should concentrate on the function and integrity of the
respiratory, reproductive, central nervous, and hematological systems.
Medical surveillance for respiratory disease should be conducted using the
principles and methods recommended by the American Thoracic
Society.
A preplacement medical evaluation is recommended to assess medical
conditions that may be aggravated or may result in increased risk when a
worker is exposed to nitrous oxide at or below the prescribed exposure limit.
The health care professional should consider the probable frequency,
intensity, and duration of exposure as well as the nature and degree of any
applicable medical condition. Such conditions (which should not be regarded
as absolute contraindications to job placement) include a history and other
findings consistent with diseases of the respiratory, reproductive, central
nervous, or hematological systems.
* Periodic medical evaluations
Occupational health interviews and physical examinations should be
performed at regular intervals during the employment period, as mandated by
any applicable Federal, State, or local standard. Where no standard exists
and the hazard is minimal, evaluations should be conducted every 3 to 5 years
or as frequently as recommended by an experienced occupational health
physician. Additional examinations may be necessary if a worker develops
symptoms attributable to nitrous oxide exposure. The interviews,
examinations, and medical screening tests should focus on identifying the
adverse effects of nitrous oxide on the respiratory, reproductive, central
nervous, or hematological systems. Current health status should be compared
with the baseline health status of the individual worker or with expected
values for a suitable reference population.
* Termination medical evaluations
The medical, environmental, and occupational history interviews, the
physical examination, and selected physiologic or laboratory tests that were
conducted at the time of placement should be repeated at the time of job
transfer or termination to determine the worker's medical status at the end
of his or her employment. Any changes in the worker's health status should
be compared with those expected for a suitable reference
population.
* Biological monitoring
Biological monitoring involves sampling and analyzing body tissues
or fluids to provide an index of exposure to a toxic substance or metabolite.
No biological monitoring test acceptable for routine use has yet been
developed for nitrous oxide.
WORKPLACE MONITORING AND MEASUREMENT
Determination of a worker's exposure to airborne nitrous oxide can be made
using one of the following techniques: 1) a Landauer Passive Dosimeter badge,
which can be used for a minimum sampling duration of 1 hour (maximum duration
40 hours). Analysis is performed by the manufacturer of the badge as
described in the OSHA Computerized Information System [OSHA 1994], or 2) an
ambient air or bag sample with a minimum collection volume of two
spectrophotometer cell volumes. Analysis is conducted using a
long-pathlength portable infrared spectrophotometer as described in NIOSH
Method No. 6600 [NIOSH 1994b].
PERSONAL HYGIENE PROCEDURES
If liquid nitrous oxide contacts the skin, workers should flush the affected
areas immediately with tepid water to reduce the likelihood of frostbite.
STORAGE
Nitrous oxide should be stored in a cool, dry, well-ventilated area in
tightly sealed containers that are labeled in accordance with OSHA's Hazard
Communication Standard [29 CFR 1910.1200]. Containers of nitrous oxide
should be protected from physical damage and should be stored separately from
cylinders containing oxygen. Nitrous oxide should also be stored separately
from aluminum, boron, hydrazine, lithium hydride, phenyllithium, phosphine,
sodium, tungsten carbide, hydrogen, hydrogen sulfide, organic peroxides,
ammonia, and carbon monoxide.
SPILLS AND LEAKS
In the event of a spill or leak involving nitrous oxide (liquid or gas),
persons not wearing protective equipment and clothing should be restricted
from contaminated areas until cleanup has been completed. The following
steps should be undertaken following a spill or leak:
1. Do not touch the spilled material; stop the leak if it is possible to
do so without risk.
2. Use water spray to protect persons attempting to stop the leak.
3. Notify safety personnel of large spills or leaks.
4. Minimize all sources of ignition because a fire may cause nitrous oxide
to accelerate the burning of other combustibles; keep combustible materials
(wood, paper, oil, etc.) away from the spilled material.
5. Isolate the area until the gas has dispersed.
SPECIAL REQUIREMENTS
U.S. Environmental Protection Agency (EPA) requirements for emergency
planning, reportable quantities of hazardous releases, community
right-to-know, and hazardous waste management may change over time. Users
are therefore advised to determine periodically whether new information is
available.
* Emergency planning requirements
Nitrous oxide is not subject to EPA emergency planning requirements
under the Superfund Amendments and Reauthorization Act (SARA) (Title III) in
42 USC 11022.
* Reportable quantity requirements for hazardous releases
Employers are not required by the emergency release notification
provisions in 40 CFR Part 355.40 to notify the National Response Center of an
accidental release of nitrous oxide; there is no reportable quantity for this
substance.
* Community right-to-know requirements
Employers are not required by EPA in 40 CFR Part 372.30 to submit a
Toxic Chemical Release Inventory form (Form R) to EPA reporting the amount of
nitrous oxide emitted or released from their facility annually.
* Hazardous waste management requirements
EPA considers a waste to be hazardous if it exhibits any of the
following characteristics: ignitability, corrosivity, reactivity, or
toxicity as defined in 40 CFR 261.21-261.24. Under the Resource Conservation
and Recovery Act (RCRA) [40 USC 6901 et seq.], EPA has specifically listed
many chemical wastes as hazardous. Although nitrous oxide is not
specifically listed as a hazardous waste under RCRA, EPA requires employers
to treat waste as hazardous if it exhibits any of the characteristics
discussed above.
Providing detailed information about the removal and disposal of
specific chemicals is beyond the scope of this guideline. The U.S.
Department of Transportation, EPA, and State and local regulations should be
followed to ensure that removal, transport, and disposal of this substance
are conducted in accordance with existing regulations. To be certain that
chemical waste disposal meets EPA regulatory requirements, employers should
address any questions to the RCRA hotline at (703) 412-9810 (in the
Washington, D.C. area) or toll-free at (800) 424-9346 (outside Washington,
D.C.). In addition, relevant State and local authorities should be contacted
for information on any requirements they may have for the waste removal and
disposal of this substance.
RESPIRATORY PROTECTION
* Conditions for respirator use
Good industrial hygiene practice requires that engineering controls
be used where feasible to reduce workplace concentrations of hazardous
materials to the prescribed exposure limit. However, some situations may
require the use of respirators to control exposure. Respirators must be worn
if the ambient concentration of nitrous oxide exceeds prescribed exposure
limits. Respirators may be used (1) before engineering controls have been
installed, (2) during work operations such as maintenance or repair
activities that involve unknown exposures, (3) during operations that require
entry into tanks or closed vessels, and (4) during emergencies. Workers
should only use respirators that have been approved by NIOSH and the Mine
Safety and Health Administration (MSHA).
* Respiratory protection program
Employers should institute a complete respiratory protection program
that, at a minimum, complies with the requirements of OSHA's Respiratory
Protection Standard [29 CFR 1910.134]. Such a program must include
respirator selection, an evaluation of the worker's ability to perform the
work while wearing a respirator, the regular training of personnel,
respirator fit testing, periodic workplace monitoring, and regular respirator
maintenance, inspection, and cleaning. The implementation of an adequate
respiratory protection program (including selection of the correct
respirator) requires that a knowledgeable person be in charge of the program
and that the program be evaluated regularly. For additional information on
the selection and use of respirators and on the medical screening of
respirator users, consult the latest edition of the NIOSH Respirator Decision
Logic [NIOSH 1987b] and the NIOSH Guide to Industrial Respiratory Protection
[NIOSH 1987a].
PERSONAL PROTECTIVE EQUIPMENT
Workers should use appropriate personal protective clothing and equipment
that must be carefully selected, used, and maintained to be effective in
preventing skin contact with liquid nitrous oxide. The selection of the
appropriate personal protective equipment (PPE) (e.g., gloves, sleeves,
encapsulating suits) should be based on the extent of the worker's potential
exposure to liquid nitrous oxide and the PPE material's ability to protect
workers from frostbite. There are no published reports on the resistance of
various materials to permeation by liquid nitrous oxide.
To evaluate the use of PPE materials with liquid nitrous oxide, users should
consult the best available performance data and manufacturers'
recommendations. Significant differences have been demonstrated in the
chemical resistance of generically similar PPE materials (e.g., butyl)
produced by different manufacturers. In addition, the chemical resistance of
a mixture may be significantly different from that of any of its neat
components.
Any chemical-resistant clothing that is used should be periodically
evaluated to determine its effectiveness in preventing dermal contact. Safety
showers and eye wash stations should be located close to operations that
involve nitrous oxide.
Splash-proof chemical safety goggles or face shields (20 to 30 cm long,
minimum) should be worn during any operation in which a solvent, caustic, or
other toxic substance may be splashed into the eyes.
In addition to the possible need for wearing protective outer apparel (e.g.,
aprons, encapsulating suits), workers should wear work uniforms, coveralls,
or similar full-body coverings that are laundered each day. Employers should
provide lockers or other closed areas to store work and street clothing
separately. Employers should collect work clothing at the end of each work
shift and provide for its laundering. Laundry personnel should be informed
about the potential hazards of handling contaminated clothing and instructed
about measures to minimize their health risk.
Protective clothing should be kept free of oil and grease and should be
inspected and maintained regularly to preserve its effectiveness.
Protective clothing may interfere with the body's heat dissipation,
especially during hot weather or during work in hot or poorly ventilated work
environments.
REFERENCES
ACGIH [1994]. 1994-1995 Threshold limit values for chemical substances and
physical agents and biological exposure indices. Cincinnati, OH: American
Conference of Governmental Industrial Hygienists.
ACGIH [1991]. Documentation of the threshold limit values and biological
exposure indices. 6th ed. Cincinnati, OH: American Conference of
Governmental Industrial Hygienists.
ATS [1987]. Standardization of spirometry -- 1987 update. American
Thoracic Society. Am Rev Respir Dis 136:1285-1296.
Braker W, Mossman AL [1980]. Matheson gas data book. 6th ed. Secaucus,
NJ: Matheson Gas Products, Inc.
CFR. Code of Federal regulations. Washington, DC: U.S. Government
Printing Office, Office of the Federal Register.
DOT [1993]. 1993 Emergency response guidebook, guides 14, 23. Washington,
DC: U.S. Department of Transportation, Office of Hazardous Materials
Transportation, Research and Special Programs Administration.
Genium [1988]. Material safety data sheet No. 109. Schenectady, NY: Genium
Publishing Corporation.
Grant WM [1986]. Toxicology of the eye. 3rd ed. Springfield, IL: Charles
C Thomas.
Hathaway GJ, Proctor NH, Hughes JP, and Fischman ML [1991]. Proctor and
Hughes' chemical hazards of the workplace. 3rd ed. New York, NY: Van
Nostrand Reinhold.
Lewis RJ, ed. [1993]. Hawley's condensed chemical dictionary. 12th ed. New
York, NY: Van Nostrand Reinhold Company.
Mickelsen RL, Hall RC [1987]. A breakthrough time comparison of nitrile and
neoprene glove materials produced by different glove manufacturers. Am Ind
Hyg Assoc J 48(11): 941-947.
Mickelsen RL, Hall RC, Chern RT, Myers JR [1991]. Evaluation of a simple
weight-loss method for determining the permeation of organic liquids through
rubber films. Am Ind Hyg Assoc J 52(10): 445-447.
NFPA [1986]. Fire protection guide on hazardous materials. 9th ed. Quincy,
MA: National Fire Protection Association.
NIOSH [1987a]. NIOSH guide to industrial respiratory protection.
Cincinnati, OH: U.S. Department of Health and Human Services, Public Health
Service, Centers for Disease Control, National Institute for Occupational
Safety and Health, DHHS (NIOSH) Publication No. 87-116.
NIOSH [1987b]. NIOSH respirator decision logic. Cincinnati, OH: U.S.
Department of Health and Human Services, Public Health Service, Centers for
Disease Control, National Institute for Occupational Safety and Health, DHHS
(NIOSH) Publication No. 87-108.
NIOSH [1992]. Recommendations for occupational safety and health:
Compendium of policy documents and statements. Cincinnati, OH: U.S.
Department of Health and Human Services, Public Health Service, Centers for
Disease Control, National Institute for Occupational Safety and Health, DHHS
(NIOSH) Publication No. 92-100.
NIOSH [1994a]. Registry of toxic effects of chemical substances: Nitrous
oxide. Cincinnati, OH: U.S. Department of Health and Human Services, Public
Health Service, Centers for Disease Control, National Institute for
Occupational Safety and Health, Division of Standards Development and
Technology Transfer, Technical Information Branch.
NIOSH [1994b]. NIOSH manual of analytical methods. 4th ed. Cincinnati, OH:
U.S. Department of Health and Human Services, Public Health Service, Centers
for Disease Control, National Institute for Occupational Safety and Health,
DHHS (NIOSH) Publication No. 94-113.
NIOSH [1994c]. NIOSH pocket guide to chemical hazards. Cincinnati, OH:
U.S. Department of Health and Human Services, Public Health Service, Centers
for Disease Control, National Institute for Occupational Safety and Health,
DHHS (NIOSH) Publication No. 94-116.
NLM [1993]. Hazardous substances data bank: Nitrous oxide. Bethesda, MD:
National Library of Medicine.
OSHA [1994]. Computerized information system. Washington, DC: U.S.
Department of Labor, Occupational Safety and Health Administration.
Parmeggiani L [1983]. Encyclopedia of occupational health and safety. 3rd
rev. ed. Geneva, Switzerland: International Labour Organisation.
Rom WN [1992]. Environmental and occupational medicine. 2nd ed. Boston,
MA: Little, Brown and Company.
Sax NI, Lewis RJ [1989]. Dangerous properties of industrial materials. 7th
ed. New York, NY: Van Nostrand Reinhold Company.
Sittig M [1991]. Handbook of toxic and hazardous chemicals. 3rd ed. Park
Ridge, NJ: Noyes Publications.
USC. United States code. Washington. DC: U.S. Government Printing Office.
Windholz M, ed. [1983]. Merck Index 10th ed. Rahway, NJ: Merck & Company.
|