EH-0395, Hydrogen Sulfide

                       ENVIRONMENT, SAFETY & HEALTH
                           HEALTH HAZARDS ALERT

           Assistant Secretary for Environment, Safety & Health
U.S. Department of Energy                             Washington, D.C.  20585
DOE/EH-0395                    Issue No. 94-1                       July 1994
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                              Hydrogen Sulfide
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EXPOSURE TO HYDROGEN SULFIDE

Hydrogen sulfide is a colorless, poisonous gas with the characteristic odor of
rotten eggs.  It is generated as a common by-product of many industrial and
manufacturing processes and during the decomposition of sulfur-containing
compounds.  Hydrogen sulfide is found in natural gas, volcanic gas, and
certain natural spring waters.  It may be encountered in the manufacture of
dyes and pigments, synthetic petroleum products, and mining processes.
Exposures may occur during hydrocarbon research and development activities, in
certain utility confined spaces, and at sewage and various waste treatment
plants.

The Occupational Safety and Health Administration (OSHA) permissible exposure
limit (PEL) for hydrogen sulfide of 10 ppm is set 30 times lower than the
"immediately dangerous to life and health" level of 300 ppm set by the
National Institute for Occupational Safety and Health (NIOSH).  Despite a low
human odor threshold for the gas in air (<< 1 ppm), hydrogen sulfide is
considered to be an insidious poison because our sense of smell rapidly
fatigues, and therefore, fails to provide a good warning of gas concentration.

The principal route of exposure to hydrogen sulfide is inhalation.  Like
carbon monoxide and the cyanides, hydrogen sulfide is classified as a chemical
asphyxiant.  Exposures to this gas can interfere with cellular respiration and
cause death if an individual's cells are deprived of oxygen (biochemical
suffocation).  At low concentrations (i.e., < 10 ppm), hydrogen sulfide causes
irritation of the eyes, mucous membranes, and upper respiratory system.  When
exposed to higher concentrations (10-50 ppm), persons tend to experience mild
eye and upper respiratory irritation, headaches, and dizziness.
Concentrations from about 50-200 ppm can cause severe eye and respiratory
tract irritation, acute conjunctivitis, lacrimation, and difficulty breathing,
as well as a sudden loss of consciousness.  Prolonged exposures at these
levels may lead to bronchitis, pneumonitis, and migraine headaches.  At higher
levels, hydrogen sulfide can cause a severe loss of motor coordination, coma,
pulmonary edema, respiratory paralysis, and ultimately death.

PROTECTION REQUIRED

The best protection from overexposure to hydrogen sulfide is regular
monitoring to identify areas and operations likely to exceed OSHA's PEL.  Work
procedures should include the use of direct reading instruments when entering
confined spaces such as man-holes, tanks, pits, and large reaction vessels
that may contain or accumulate hydrogen sulfide gas.  Areas that routinely
pose overexposure hazards should be equipped with continuous monitoring
instruments.  Where exposures cannot be otherwise reduced with engineering
equipment and ventilation systems, it may be necessary to use supplied air
respirators (i.e., airline type or self-contained breathing apparatus).

If you have any questions about your workplace procedures, potential
exposures, or the use of personal protective equipment, contact your local
safety and health officer or Carlos Coffman, Industrial Hygiene Program
Division, EH-412, at (301) 903-5493.

This Safety & Health Hazards Alert is one in a series of publications issued
by EH to share occupational safety and health information throughout the DOE
complex. To be added to the Distribution List or to obtain copies of the
publication, call (301) 916-4444. For additional information regarding the
publications, call Barbara Bowers, (301) 903-3016.