This month our example is Sulfur
Dioxide, which has a chemical formula of SO2.
Sulfur Dioxide is listed under the UN # (United Nations
Number) by the US Department of Transportation: UN 1079
and has a CAS # of 7446-09-5.
Persons exposed only to sulfur
dioxide gas pose no risk of secondary contamination.
Persons whose skin or clothing is contaminated with
liquid sulfur dioxide can secondarily contaminate
rescuers by direct contact or through off gassing of
vapor. At room temperature, sulfur dioxide is a
nonflammable, colorless gas that is heavier than air.
Its strong, pungent odor and irritating properties
usually provide adequate warning of its presence.
Sulfur dioxide is severely irritating
to the eyes, mucous membranes, skin, and respiratory
tract. Bronchospasm, pulmonary edema, pneumonitis, and
acute airway obstruction can occur.
Inhalation exposure to very low
concentrations of sulfur dioxide can aggravate chronic
pulmonary diseases, such as asthma and emphysema.
Certain highly sensitive asthmatics may develop
bronchospasm when exposed to sulfur dioxide or
Sulfur dioxide reacts with water in
the upper airway to form sulfurous acid, bisulfite, and
sulfite, all of which induce irritation. As a result,
reflex bronchoconstriction increases airway resistance.
gas at room temperature, colorless liquid when
pressurized or cooled.
point: (760 mm Hg): 14.0 °F (-10.0 °C)
Freezing point: -99.4
°F (-72.7 °C)
pressure: 2,538 mm Hg at 70.0°F (21.1 °C)
density: 1.43 g/mL (water = 1.00)
solubility: soluble in water (11.3 g/100 mL at 68 °F
At room temperature, sulfur dioxide is a
nonflammable, colorless gas with a very strong, pungent
odor. Most people can smell sulfur dioxide at levels of
0.3 to 1 ppm. It is handled and transported as a
liquefied compressed gas. It easily dissolves in water.
The liquid is heavier than water. Although sulfur
dioxide does not burn in air, cylinders of compressed
liquid can explode in the heat of a fire, i.e., the
tanks can BLEVE.
Sulfur dioxide gas is released primarily from the
combustion of fossil fuels (75% to 85% of the industrial
sources), the smelting of sulfide ores, volcanic
emissions, and several other natural sources. It is a
U.S. EPA priority air pollutant, but has many industrial
and agricultural uses. It is sometimes added as a
warning marker and fire retardant to liquid grain
fumigants. Approximately 300,000 tons are used each year
to manufacture hydrosulfites and other sulfur-containing
chemicals; to bleach wood pulp and paper; to process,
disinfect, and bleach food; for waste and water
treatment; in metal and ore refining; and in oil
refining. Toxic amounts of sulfur dioxide can be
released from the preservative chemical metabisulfite in
the presence of water and acid.
include sulfur oxide, sulfurous acid anhydride,
sulfurous anhydride, and sulfurous oxide.
Standards and Guidelines
(permissible exposure limit) = 5 ppm (averaged over an
(immediately dangerous to life or health) = 100 ppm
ERPG-2 (maximum airborne concentration below which it is
believed that nearly all persons could be exposed for up
to 1 hour without experiencing or developing
irreversible or other serious health effects or symptoms
that could impair their abilities to take protective
action) = 3 ppm
Sulfur dioxide dissolves in water or steam to form
sulfurous acid. Liquid sulfur dioxide corrodes iron,
brass, copper, and some forms of plastic and rubber.
Many metals, including zinc, aluminum, cesium, and iron,
incandesce and/or ignite in unheated sulfur dioxide.
Sulfur dioxide reacts explosively when it comes in
contact with sodium hydride. Sulfur dioxide ignites when
it is mixed with lithium acetylene carbide diamino or
lithium acetylide ammonia.
Exposure Sulfur dioxide dissolves in the moisture on
skin, eyes, and mucous membranes to form sulfurous acid,
an irritant and inhibitor of mucociliary transport. Most
of the inhaled sulfur dioxide is detoxified by the liver
to sulfates and excreted in the urine. The bisulfite ion
produced when sulfur dioxide reacts with water is likely
to be the main initiator of sulphur dioxide-induced
bronchoconstriction. Children do not always respond to
chemicals in the same way that adults do. Different
protocols for managing their care may be needed.
- Sulfur dioxide respiratory irritation induces
symptoms such as sneezing, sore throat, wheezing,
shortness of breath, chest tightness, and a feeling of
suffocation. Reflex laryngeal spasm and edema can cause
acute airway obstruction. Bronchospasm, pneumonitis, and
pulmonary edema can occur. Some individuals are very
susceptible to the presence of sulfur dioxide and
overreact to concentrations which, in most people,
elicit a much milder response. This hyperreactive
response occurs the first time the individual is exposed
and is therefore not an acquired immune or
“hypersensitivity” response. Acclimatization (a
physiological adjustment of the individual to
environmental changes) may also occur in up to 80% of
exposed individuals. This is not necessarily beneficial
although exposure may become less subjectively
objectionable upon continuous or repeated exposure.
Asthmatics who are sensitive to sulfites in food can
develop bronchospasm or an anaphylactoid reaction.
Sulfur dioxide, along with other components of air
pollution, can exacerbate chronic cardiopulmonary
to high concentrations of sulfur dioxide can lead to
Reactive Airway Dysfunction Syndrome (RADS), a
chemically- or irritant-induced type of asthma.
may be more vulnerable to corrosive agents than adults
because of the relatively smaller diameter of their
airways. Children also may be more vulnerable because of
relatively increased minute ventilation per kg and
failure to evacuate an area promptly when exposed.
Sulfur dioxide is a severe skin irritant causing
stinging pain, redness, and blisters, especially on
mucous membranes. Skin contact with escaping compressed
gas or liquid sulfur dioxide can cause frostbite and
irritation injury. Because of their relatively larger
surface area: body weight ratio, children are more
vulnerable to toxicants that affect the skin.
Conjunctivitis and corneal burns can result from the
irritant effect of sulfur dioxide vapor or escaping
compressed gas, and from direct exposure to the liquid.
Nausea, vomiting, and abdominal pain have been
reported after inhalation exposure to moderate to high
doses of sulfur dioxide.
Sequelae High-level acute exposures have resulted in
pulmonary fibrosis, chronic bronchitis, and chemical
bronchopneumonia with bronchiolitis obliterans.
Bronchospasm can be triggered in individuals who have
underlying lung disease, especially those who have
asthma and emphysema. Rarely, new onset airway
hyperreactivity, known as reactive airways dysfunction
syndrome (RADS), develops in patients without prior
Exposure can result in an altered sense of smell
(including increased tolerance to low levels of sulfur
dioxide), increased susceptibility to respiratory
infections, symptoms of chronic bronchitis, and
accelerated decline in pulmonary function. Chronic
exposure may be more serious for children because of
their potential longer life span.
The International Agency for Research on Cancer
(IARC) assigned sulfur dioxide to Group 3, not
classifiable as to its carcinogenicity to humans.
Reproductive and Developmental
Effects - Sulfur dioxide is 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
consequences. There are no known reproductive or
developmental effects of sulfur dioxide alone by any
route of exposure. There is no conclusive evidence that
sulfur dioxide is a genotoxin in humans.
In using the PEAC application we
access information for the chemical by first locating
Sulfur Dioxide 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 Sulfur Dioxide using the PEAC-WMD for Windows
Review of the information displayed
in the chemical properties screen whether in Figure 1
(above) or Figures 2-4 (below), show chemical properties
values discussed earlier at the top of this discussion.
As you can see, the published toxicity values, e.g.,
IDLH 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
PAD a little later.
Figure 2 – Selecting Sulfur
Dioxide using the PEAC-WMD for Pocket PC
Figure 3 – The top portion of the
Chemical Properties Data Display Screen
Figure 4– The bottom portion of
the Chemical Properties Data Display Screen
The PEAC-WMD application provides
more than just the Chemical Properties for the
identified material, the Chemical Properties are
just the default information screen displayed, by
clicking (if running the Windows version, see Figure 5)
or tapping (if running the Pocket PC version, see Figure
6) on the drop-down box where Chemical Properties
is displayed on the screen, the user is provided with a
list of other databases that provide information for the
selected chemical (Sulfur Dioxide in our current
example). So the search is done once, and the user is
indexed into the different databases easily and quickly.
Figure 5 – Accessing other
databases from the PEAC-WMD for Windows
Figure 6 – Accessing other
databases from the PEAC-WMD for Pocket PC
A quick review or sampling of the
type of information available in each of these screens
is now provided. First is access to Respirators
Recommendations, these are primarily taken from the
NIOSH Pocket Guide and provide the user with different
types of respirators for increasing concentrations. A
sample of the information is provided in Figure 7.
Likewise the Chemical Protective Clothing (CPC)
database can be accessed by clicking on either the
All Chemical Protective Clothing or the
Available Chemical Protective Clothing selection
as shown in Figure 8. The All Chemical Protective
Clothing displays all the CPC entries in the
PEAC‑WMD database for the selected chemical vs. the
Available Chemical Protective Clothing displays
just those CPC entries that match the manufacturers the
user has previously identified as the products the
response organization typically keeps in inventory.
Figure 7 – Respirator
Recommendations for Sulfur Dioxide
Figure 8 – Chemical Protective
Clothing for Sulfur Dioxide
The IC (Incident Commander) will
typically utilize more than a single resource for
developing a response plan but sometimes the information
in other resources will use a different name for the
same substance. Clicking on the Synonyms
selection will provide a quick list of other names
the substance may be referenced by in other resources as
shown in Figure 9. To further assist the responder in
initiating the best response plan, PEAC‑WMD also
provides the generic guidelines found in the ‘orange
pages’ of the DOT Emergency Response Guidebook (ERG).
These are categorized into different types of procedures
depending on the incident and the problem to be
mitigated. An example for Spill or Leak Response
is shown in Figure 10.
|Figure 9 – Synonyms
||Figure 10 – ERG Spill or
Leak Response |
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.
Because of its boiling point Sulfur Dioxide will be
released from a container as a vapor or aerosol or a
liquid that will rapidly vaporize. As with all 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
Sulfur Dioxide as the involved chemical we’ll set the
location to be a manufacturing facility outside of St.
Louis. A new hired driver of a fork lift has driven
beneath a Sulfur Dioxide storage tank and clipped a 2’
valve which is now venting liquid and vapor from the
bottom of the tank. The tank is mounted vertically, 10
foot in diameter, 40 foot long, and about 50% full of
material. The time is 8:30 AM on August 12th,
the temperature is 90°F with overcast skies and winds
are about 5 mph. There are manufacturing and commercial
areas nearby and light traffic on a nearby highway
downwind. The PEAC tool can provide guidance with
regards to toxic vapor clouds that are released.
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 11. Following through the screens, we
provide information on the Meteorology, Container Size,
and Type of Release (Source). If you decide to follow
along on this example, remember to change the location
to St. Louis and the time to 8:30 AM, August
It’s St. Louis in August and
the temperature about 90°, wind is set for 5 mph,
overcast so we’ll set cloud cover to 100%, and the
terrain is Urban/Forest since it’s an industrial
We have selected from our list
of container sizes the Large Storage
selection. Then we have entered the diameter,
length and set the % full to 50%. The default
Orientation of the tank is vertical.
As the scenario calls for,
we’ve selected Hole of pipe Release as the
Source type of release. The default Hole
Diameter and Hole Height we will leave
unchanged at 2” and 0’
Figure 11 – Calculating a PAD using the
By pressing the right arrow at the
top of the screen, the PEAC system will display a screen
as shown in Figure 12. 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 Sulfur Dioxide.
Figure 12 – Default PAD for Sulfur
Dioxide-Using the IDLH of 100 ppm
One of the unique advantages of the
PEAC‑WMD tool is how easily the user can assess
different conditions, whether it be changing the wind
speed or temperature or another input value that would
effect the PAD. An example is to assess the impact on
evacuation or standoff distance if a different toxicity
level is considered. By tapping or clicking on the down
arrow on the field adjacent to the Level of Concern
other established toxicity values can be selected.
Figure 13 demonstrates selecting the ERPG-2 value of
|Figure 13 – Selecting a
different Level of Concern
Once the value has been selected the
PEAC‑WMD tool will calculated a new PAD. In this example
a warning message will appear since the PAD is greater
than 7.0 miles (Figure 14). The PAD will be displayed
once the user has acknowledged the warning message that
wind speed and terrain over long distances will most
Figure 14 – Warning
message if PADs greater than 7 miles are
As shown in Figure 15, the calculated
Pad is then displayed and because the concentration or
Level of Concern has dropped from 100 ppm to 3
ppm, our distance has increased
Figure 15 – PAD for 3 ppm Level of
Now we can provide the IC with some
guidance as to how far downwind people might be at risk.
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/.