This month our example is Hydrogen
Sulfide, which has a chemical formula of
(H2S). Hydrogen Sulfide is listed under the
UN # (United Nations Number) by the US Department of
Transportation: UN 1053. Hydrogen Sulfide CAS# is:
Persons exposed to hydrogen sulfide
pose no serious risks of secondary contamination to
personnel outside the Hot Zone. However, fatalities have
occurred to rescuers entering the hot zone.
Hydrogen sulfide is a colorless,
highly flammable and explosive gas produced naturally by
decaying organic matter and by certain industrial
processes. Hydrogen sulfide has a characteristic
rotten-egg odor; however, olfactory fatigue may occur
and consequently it may not provide adequate warning of
Hydrogen sulfide is well absorbed
through the lungs; cutaneous absorption is minimal.
Exposure by any route can cause systemic effects.
Hydrogen sulfide is a colorless, flammable, highly
toxic gas. It is shipped as a liquefied, compressed gas.
It has a characteristic rotten-egg odor that is
detectable at concentrations as low as 0.5 ppb.
Hydrogen sulfide is produced naturally by decaying
organic matter and is released from sewage sludge,
liquid manure, sulfur hot springs, and natural gas. It
is a by-product of many industrial processes including
petroleum refining, tanning, mining, wood pulp
processing, rayon manufacturing, sugar-beet processing,
and hot-asphalt paving. Hydrogen sulfide is used to
produce elemental sulfur, sulfuric acid, and heavy water
for nuclear reactors.
Colorless gas with odor of rotten eggs
properties: Not dependable; characteristic
rotten-egg odor detectable at about 0.5 ppb, but
olfactory nerve fatigue occurs in 2 to 15 minutes at
concentrations over 100 ppm
weight: 34.1 daltons
point: (760 mm Hg): -77 °F (-60.3 °C)
pressure: >760 mm Hg at 68 °F (20 °C)
density: 1.2 (air = 1)
solubility: Slightly water soluble (0.4% at 68 °F [20 °C])
Highly flammable and explosive between 4% and 45%
(concentration in air); may travel to a source of
ignition and flash back. Burns to produce a toxic gas,
dihydrogen sulfide, sulfur hydride, sulfurated hydrogen,
hydrosulfuric acid, “sewer gas,” “swamp gas,” hepatic
acid, sour gas, and “stink damp.”
Standards and Guidelines:
ceiling = 20 ppm
maximum peak = 50 ppm (10 minutes, once, no other
(immediately dangerous to life or health) =100 ppm
ERPC-2 (emergency response planning guideline) (maximum
airborne concentration below which it is believed that
nearly all individuals could be exposed for up to 1 hour
without experiencing or developing irreversible or other
serious health effects or symptoms which could impair an
individual’s ability to take protective action) = 30
Incompatibilities: Hydrogen sulfide
reacts with strong oxidizers, strong nitric acid, and
Routes of Exposure:
Inhalation is the major route of hydrogen sulfide
exposure. The gas is rapidly absorbed by the lungs. The
odor threshold (0.5 ppb) is much lower than the OSHA
ceiling (20 ppm). However, although its strong odor is
readily identified, olfactory fatigue occurs at high
concentrations and at continuous low concentrations. For
this reason, odor is not a reliable indicator of
hydrogen sulfide’s presence and may not provide adequate
warning of hazardous concentrations. Hydrogen
sulfide is slightly heavier than air and may accumulate
in enclosed, poorly ventilated, and low-lying areas.
exposed to the same levels of hydrogen sulfide as adults
may receive larger doses because they have greater lung
surface area: body weight ratios and increased minute
volumes: weight ratios. In addition, they may be exposed
to higher levels than adults in the same location
because of their short stature and the higher levels of
hydrogen sulfide found nearer to the ground. Children
may be more vulnerable to corrosive agents than adults
because of the relatively smaller diameter of their
Contact Prolonged exposure to hydrogen sulfide, even
at relatively low levels, may result in painful
dermatitis and burning eyes. Direct contact with the
liquefied gas can cause frostbite. Absorption through
intact skin is minimal.
Because hydrogen sulfide is a gas at room
temperature, ingestion is unlikely to occur.
sulfide is a mucous membrane and respiratory tract
irritant; pulmonary edema, which may be immediate or
delayed, can occur after exposure to high
of acute exposure include nausea, headaches, delirium,
disturbed equilibrium, tremors, convulsions, and skin
and eye irritation.
of high concentrations of hydrogen sulfide can produce
extremely rapid unconsciousness and death. Exposure to
the liquified gas can cause frostbite injury.
Acute Exposure Hydrogen
sulfide’s can cause inhibition of the cytochrome oxidase
enzyme system resulting in lack of oxygen use in the
cells. Anaerobic metabolism causes accumulation of
lactic acid leading to an acid-base imbalance. The
nervous system and cardiac tissues are particularly
vulnerable to the disruption of oxidative metabolism and
death is often the result of respiratory arrest.
Hydrogen sulfide also irritates skin, eyes, mucous
membranes, and the respiratory tract. Pulmonary effects
may not be apparent for up to 72 hours after exposure.
not always respond to chemicals in the same way that
adults do. Different protocols for managing their care
may be needed.
CNS injury is immediate and significant after
exposure to hydrogen sulfide. At high concentrations,
only a few breaths can lead to immediate loss of
consciousness, coma, respiratory paralysis, seizures,
and death. CNS stimulation may precede CNS depression.
Stimulation manifests as excitation, rapid breathing,
and headache; depression manifests as impaired gait,
dizziness, and coma, possibly progressing to respiratory
paralysis and death. In addition, decreased ability to
smell hydrogen sulfide occurs at concentrations greater
than 100 ppm.
Inhaled hydrogen sulfide initially affects the nose
and throat. Low concentrations (50 ppm) can rapidly
produce irritation of the nose, throat, and lower
respiratory tract. Pulmonary manifestations include
cough, shortness of breath, and bronchial or lung
hemorrhage. Higher concentrations can provoke bronchitis
and cause accumulation of fluid in the lungs, which may
be immediate or delayed for up to 72 hours. Lack of
oxygen may result in blue skin color.
be more vulnerable to corrosive agents than adults
because of the relatively smaller diameter of their
airways. Children may also be more vulnerable to gas
exposure because of increased minute ventilation per
unit weight of the child and failure to evacuate an area
promptly when exposed.
High-dose exposures may cause insufficient cardiac
output, irregular heartbeat, and conduction
Transient renal effects include blood, casts, and
protein in the urine. Renal failure as a direct result
of hydrogen sulfide toxicity has not been described,
although it may occur secondary to cardiovascular
Symptoms may include nausea and vomiting.
Prolonged or massive exposure may cause burning,
itching, redness, and painful inflammation of the skin.
Exposure to the liquified gas can cause frostbite
Eye irritation may result in inflammation (i.e.,
keratoconjunctivitis) and clouding of the eye surface.
Symptoms include blurred vision, sensitivity to light,
and spasmodic blinking or involuntary closing of the
Sequelae Inflammation of the bronchi can be a late
development. Survivors of severe exposure may develop
psychological disturbances and permanent damage to the
brain and heart. The cornea may be permanently scarred.
Hydrogen sulfide does not accumulate in the
body. Nevertheless, repeated or prolonged exposure has
been reported to cause low blood pressure, headache,
nausea, loss of appetite, weight loss, ataxia,
eye-membrane inflammation, and chronic cough. Neurologic
symptoms, including psychological disorders, have been
associated with chronic exposure. Chronic exposure may
be more serious for children because of their potential
longer latency period.
sulfide has not been classified for carcinogenic
Reproductive and Developmental
Effects There is some evidence to suggest that
exposure to hydrogen sulfide may be associated with an
increased risk of spontaneous abortion. No information
was located pertaining to placental transfer of hydrogen
sulfide or to excretion of hydrogen sulfide in breast
milk. There are no studies of developmental effects in
humans exposed to hydrogen sulfide. However, results
from animal studies suggest that hydrogen sulfide may be
a developmental neurotoxicant. Hydrogen sulfide is not
listed in TERIS or in Shepard’s Catalog of
Teratogenic Agents. It is also not included in
Reproductive and Developmental Toxicants, a 1991
report published by the U.S. General Accounting Office
(GAO) that lists 30 chemicals of concern because of
widely acknowledged reproductive and developmental
In using the PEAC application we
access information for the chemical by first locating
Hydrogen Sulfide in the database. The following figures
show the screens displayed for chemical properties,
Figure 1 for the PEAC-WMD for Windows application
and Figure 2-5 for the PEAC‑WMD for the Pocket PC
Figure 1 - Using the Lookup By: Name for
Hydrogen Sulfide using the PEAC-WMD for Windows
Review of the information displayed
in the chemical properties screen whether in Figure 1
(above) or Figures 2-5 (below), show chemical properties
values discussed earlier at the top of this discussion.
As you can see below, the published toxicity values,
e.g., IDLH, ERPGs, and the TEELs (Temporary Emergency
Exposure Limits) published by Department of Energy are
provided. We will use the IDLH as the Level of Concern
when we develop the Protective Action Distance (PAD) a
Figure 2 – Selecting Hydrogen
Sulfide using the PEAC-WMD for Pocket PC
Figure 3 – The top portion of the
Chemical Properties Data Display Screen
Figure 4 – The middle portion of
the Chemical Properties Data Display Screen
Figure 5– The bottom portion of
the Chemical Properties Data Display Screen
A benefit of using the PEAC tool is
assistance in the development of an evacuation zone for
those chemicals that produce a toxic vapor cloud. If
transported as a compressed liquefied vapor, it will be
released from a container as a vapor or aerosol or a
liquid that will rapidly vaporize. As with most of our
examples, AristaTek creates a scenario for a spill or
release of the specific chemical, and then we work
through the development of a PAD (Protective Action
Distance) to demonstrate how the PEAC system works.
For our hypothetical scenario using
Hydrogen Sulfide as the involved chemical we’ll set the
location to be a natural gas processing facility located
just outside Evanston, WY. The date is January 14, 2004,
about 4:45 PM with a temperature of 35°F, a wind speed
of 5 mph with a clear sky. The release involves a
low-pressure gas line that contains hydrogen sulfide
that runs from the scrubbing unit to a flare, and a
1-inch valve has been knocked off. To provide some
additional information, we’ll specify the pipeline is a
6-inch diameter line about 500 feet long. The PEAC tool
can provide guidance with regards to toxic vapor cloud
that is released.
If you decide to follow along as we
proceed through these examples, remember to set the
location to Evanston, WY (Salt Lake City is pretty close
and is in the list of locations built into the PEAC
locations list) and set the date and time to the proper
values, otherwise you’ll compute different values. We’ll
use a terrain type of crops/brush since most of the
surrounding vegetation is probably sagebrush for a gas
processing facility in Wyoming.
As seen at the top of the data
display screens, there is a yellow icon displayed; this
is the PEAC icon for notifying the user that a
Protective Action Distance can be calculated. Clicking
or tapping on the PAD icon will display a screen as
shown in Figure 6. Following through the screens, we
provide information on the Meteorology, Container Size,
and Type of Release (Source). The following figures
demonstrate how we would work through our scenario to
see what our Protective Action Distance should
It’s Wyoming in December and
the temperature about 35°, wind is set for 2 mph,
clear skies and the terrain is Crops/Brush
since it’s an outdoor setting around a gas
We have selected from our list
of container sizes the Pipeline selection
with a 6” line (0.5’ diameter) and a 500’ length.
This gets us a quick estimate of how much material
might be involved.
We have selected a Hole or
Pipe Release for the type of release with a 1”
Hole Diameter. This is the size of the
valve knocked off the flare line.
Figure 6 – Calculating a PAD using the
PEAC‑WMD System for January 14th
By pressing the right arrow at the
top of the screen, the PEAC system will display a screen
as shown in Figure 7. This calculates a PAD
(Protective Action Distance) based on the default
Level of Concern the IDLH of 100 ppm. This
evacuation or standoff distance is based on the toxicity
of Hydrogen Sulfide, not the flammability.
Figure 7 – Default PAD for Hydrogen
Sulfide using the IDLH of 100 ppm
With a wind speed of 5 mph the
downwind evacuation or PAD extends about 2 mile. If the
wind speed was slower so that stable atmospheric
conditions were established, the downwind evacuation
distance will be impacted. To see the effect, click on
the left arrow [|] at the top
of the screen until you return to the meteorological
input screen. As shown in Figure 8, select a wind speed
of 2 mph rather than 5 mph.
Figure 8 – Change the wind speed
to 2 MPH
Then click on the right arrows [}] at the top
of the screen until a new PAD screen is displayed. The
results of the new calculations are shown in Figure 9.
Figure 9 – PAD under stable
As can be seen in Figure 9, the
evacuation distance has increased when stable
atmospheric conditions are present, hence the term
“worst case” conditions.
The user should be aware that stable
atmospheric conditions may exist during night with low
wind; this is a “worst case” condition. These conditions
can present serious problems with respect to toxic
clouds and their behavior.
Substantial portions of this
discussion were adapted from the Agency for Toxic
Substances and Disease Registry (ATSDR) Web site for
Medical Management Guidelines at: http://www.atsdr.cdc.gov/.