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Hydrogen sulfide, variously known as sulferetted hydrogen and hydrogen sulfuric acid, is a colorless,
flammable gas having a sweetish taste and an odor of rotten eggs. It forms naturally when sulfur-
containing organic matter decays and hence may be found in sewers, landfill areas, gypsum mines,
coal mines, railroad tunnels, oil fields, oil refineries and natural gas. It is present in certain
petroleums as high as 10-12% by volume and in refinery gases as high as 50-75%. It can also be
found following blasting with black powder and in chemical laboratories.

Hydrogen sulfide is highly flammable and burns in oxygen emitting sulfur dioxide and water. In a
low oxygen atmosphere, water and elemental sulfur is produced. It forms an explosive mixture with
oxygen between 4% and 45% by volume.

Hydrogen sulfide is a hazardous compound not only because of its toxicological properties, but
more so because of its peculiar warning properties. The odor threshold, the minimum
concentration producing a faint odor, is in the parts per billion range in air. However, continued
exposure results in a loss of sensitivity of smell and exposure continues without apparent discomfort
until acute poisoning occurs. At concentrations greater than 150-200 ppm, olfactory nerve paralysis
occurs and the warning odor disappears.


10 parts per million parts of air.


15 parts per million parts of air.


When inhaled, hydrogen sulfide is absorbed through the lungs and is mainly eliminated via the same
route. A small amount is excreted through the urine. Absorption through the skin is possible, but
at too slow a rate to produce poisoning. Hydrogen sulfide poisoning may be acute or subacute.

Subacute Poisoning: H2S poisoning is primarily manifested by swollen eyelids, itchiness, smarting,
pain, blurring of vision and possible irritation of the eyes and respiratory tract.
Acute Poisoning: H2S acts on the nervous system. In low concentrations, it has depressant effects.
In higher concentrations, it has a stimulating action and in very high concentrations (400-700 ppm),
it paralyzes the respiratory center causing cessation of respiration. Unconsciousness may occur
suddenly without warning or pain and the heart may continue to beat 5-10 minutes after breathing
has stopped. The victim dies of asphyxiation.

First Aid: A physician should be called immediately. If a person is overcome, remove to fresh air at
once. If breathing stops, apply artificial respiration while keeping victim warm. After recovery,
victim should be kept at rest.


General: Hydrogen sulfide is both a highly toxic and hazardous gas. If a worker detects the odor of
hydrogen sulfide from an uncontrolled source, the area should be evacuated until the source and
concentration are determined. The use of respirators in dangerous atmospheres (Rule 3302) applies.
 This rule requires written procedures and training, communications, stand-by personnel, and
appropriate rescue equipment.

Confined Spaces: All confined space entries must be done in accordance with the permit-required
confined spaces rules
               A POTENTIAL KILLER"
The primary and essential difference between regular crude oil and "sour" crude oil is the presence of a gas
known as hydrogen sulfide (H2S).

In very low concentrations, less than 1 part of gas in a million parts of air
(<1 ppm), it has a characteristic odor like that of rotten eggs. In high concentrations, it has other important

1.   Hydrogen sulfide is extremely toxic.               A major factor in its toxicity is its ability to fatigue
     the sense of smell. H2S loses the typical rotten eggs odor when the concentration rises, and exposed
     workers may not be aware of increased gas concentrations. Exposure to concentrations above 600
     ppm can be rapidly fatal.

2.   It causes extreme corrosion.           Corrosion of pipes, valves and fittings can cause a breakdown
     of gas and oil gathering systems and be a serious threat to employees and the public.

3.   The gas is flammable and forms explosive mixtures in a range of 4.3% to 45.5% by
     volume in air.

The following information deals primarily with the toxicity of H2S. Dismayed by a number of deaths
resulting from hydrogen sulfide, the seriousness of the hazard can be explained in the following way:

1.   "The toxicity and rapidity     of death from exposure to hydrogen sulfide approaches that of
     hydrogen cyanide.

     Cyanides have had better 'press' coverages than the sulfides. If states had exacted the death penalty
     by the use of hydrogen sulfide rather than hydrogen cyanide, we might have greater respect for the
     hydrogen sulfide hazard."

2.   "Exposure to hydrogen sulfide rapidly produces olfactory         fatigue!
     Stated more simply, it puts your nose 'out of business'. From then on, odor is no longer an indicator
     of the hazard and gas concentrations may increase to a hazardous level with no detectable change.
     The exposed individual loses the ability to gauge exposure.

     In one plant where hydrogen sulfide was released from a chemical operation, the operator was asked
     about the gas and his response was: 'Oh, do you smell hydrogen sulfide? I noticed it when I started
this morning but thought it had stopped because I haven't smelled it for some time.'"

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