SULFUR DIOXIDE
HAZARDOUS MATERIALS
CHEMICAL DATA NOTEBOOK SERIES #50
FRANK L. FIRE
Sulfur dioxide is a toxic, corrosive, irritating, colorless gas with a sharp, choking odor. It is used to make disinfectants, food preservatives, fumigants, fungicides, glass, insecticides, and many sulfur compounds. It also is used to bleach beet sugar, fruit, flour, grain, oil, and other products. Sulfur dioxide is used in glass making, leather-tanning operations, ore and metal refining, paper and pulp manufacturing, the petroleum industry, and wastewater treatment. It once had fairly wide use as a refrigerant. It usually will be liquefied for shipment and storage.
PROPERTIES
Sulfur dioxide will not burn. When liquefied, it has a specific gravity of 1.436, a molecular weight of 64, and a vapor density of 2.22. It has a vapor ‘pressure of 34.4 psig (pounds per square inch gauge) at 70°F and 69-4 psig at 10()°F. It boils at 14°F, freezes at — 104.6°F, and is somewhat solublein water, in which it forms sulfurous acid. Its molecular formula is
HAZARDS
Sulfur dioxide is a toxic gas whose odor can be detected in concentrations as low as 3 ppm (parts per million parts of air). Its TLV-TWA (threshold limit value—time weighted average) is 2 ppm and its STEL (shortterm exposure limit) is 5 ppm for 15 minutes. A concentration of 50 to 100 ppm is the maximum permissible limit for 30 to 60 minutes, while concentrations of 400 to 500 ppm are immediately dangerous to life (IDLH).
Sulfur dioxide severely irritates the mucous membranes of the eyes, nose, throat, and lungs at concentrations near 10 ppm. This occurs as the gas dissolves in moisture to form sulfurous acid. As the concentration increases, other symptoms appear such as breathing difficulty, dryness of the nose and throat, choking, coughing, and tightness of the chest. Chemical bronchopneumonitis may occur after a few hours or after one day. Repeated exposure may cause a change in ability to taste and smell, bronchitis, persistent hacking, coughing, increased fatigue, nasal discharge, and permanent lung impairment. Death may occur due to paralysis of the respiratory system, pulmonary edema, or systemic acidosis.
Above 10 ppm, irritation of the eyes increases until there is a real threat of vision loss due to permanent eye damage. Any contact of the liquid with the eyes may cause blindness.
Some skin irritation occurs at low concentrations because of acid formation as the sulfur dioxide dissolves in the moisture on the skin. Contact with the liquid causes skin burns and possibly frostbite damage.
It is not easy to ingest liquid sulfur dioxide, but on the outside chance that it occurs, expect severe irritation and burning of the mouth, esophagus, and stomach.
Sulfur dioxide, when it dissolves in water, forms sulfurous acid, which slowly oxidizes to sulfuric acid. Although the concentration of either acid ordinarily would not be very high, nevertheless it is likely to damage human tissue as well as corrode many metals. Whenever an inorganic acid attacks a metal, hydrogen is generated. While the amounts of this flammable gas generated should not reach dangerous proportions in open spaces, be aware of the reaction.
Liquid sulfur dioxide itself is corrosive to aluminum and other metals and will severely damage living tissue. It also may attack some plastic and rubber compounds.
Sulfur dioxide may react with powdered metals and sodium or potassium, producing hydrogen explosions and/or fires. It also reacts with many other materials, including organometallic compounds containing an alkali metal (lithium, sodium, potassium, or cesium) combined to form a carbide. Examples are cesium acetylene carbide, potassium acetylene carbide, lithium acetylene carbide, and sodium acetylene carbide. Sodium and potassium carbide also may react violently with sulfur dioxide. Reactions with metals such as aluminum, chromium, and manganese will occur as will reactions with acrolein, cesium monoxide, chlorine trifluoride, ferrous oxide, stannous oxide, and other groups of chemicals such as the halogens and inorganic compounds whose chemical names end in chlorate.
Whether sulfur dioxide is shipped in the gaseous or liquefied form, it will be under pressure in its container. This is always a hazard in storage, use, or transportation, since the failure of a container holding a compressed gas almost always will involve shrapnel. In some cases, the container will be propelled like a rocket if it fails at one of its ends.
Release of the liquefied gas is hazardous because of the temperature of the liquid (14°F). This may cause frostbite when it contacts human tissue.
NONFIRE RELEASE
In the release of any hazardous material, notify the proper environ-mental authorities immediately. Their response will vary according to the material involved. They arc not concerned merely with possible damage to the environment: The ERA also is ~ very concerned about the immediate hazards to the population in the event of a release of any hazardous material, and it will perform tests over extended periods of time to warn against any long-term danger to humans resulting from a hazardous-materials release.^’ The concern for a sulfur dioxide release is basically immediate and shortterm. Depending on the amount re-⅜ leased, its form, and where it was released, damage to the environment may not be as severe as with other* hazardous materials.
Whether the release is in pressurized gas or liquefied form, the main concern is spread of the gas downwind. High concentrations of sulfur dioxide may be deadly. Anyone* caught in the midst of a sulfur dioxide release may be overcome by the pungent gas and rendered helpless by the ^ choking and coughing following inhalation of large amounts of the gas. Smaller amounts may irritate the eyes* and respiratory system to the point ^ that the victim cannot see and bej comes disoriented and even incapaciw tated. Because of the toxic and/or incapacitating effect the gas has on humans, evacuation downwind and for some distance around the source of the release must be one of emergency responders’ first considerations.
The vapor density of 2.22 means that the gas will “hang together” and flow along low spots in the terrain. It will tend to accumulate in low or confined areas and pose a great hazard for anyone entering the area or space without respiratory protection.
Obviously the gas may disperse in the air faster than other forms of sulfur dioxide. The use of a highpressure water spray or fog will speed up dispersal of the gas in air, but take care to contain the runoff water, since it too will be contaminated. If the leak is the result of a puncture or other ’small hole in the container, trained responders who are fully protected from the gas can use plugging and/or patching techniques. The nonflammability of the gas enables trained responders to carry out procedures ‘without fear of ignition.
If liquid is being released from the container, it also will be expelled under pressure and will volatilize very rapidly, producing large quantities of gas. If enough liquid is released to form a pool, the liquid obviously will Jx>il if the ambient temperature is 14°F or higher. Any liquid will produce its maximum amount of vapors at its boiling point, so under most conditions of release dangerously 4large quantities of sulfur dioxide gas will be generated from liquefied sulfur dioxide.
Try any technique that will slow the evolution of gas from the pooled liquid. Building containment ponds ^>y diking dirt and other materials around a liquid release is a short-term mitigation technique, since the liquid 5 will boil rapidly. However, it does ..help reduce the spread of contamination. Liquid sulfur dioxide will seep “into the soil, reacting with moisture in the soil to form sulfurous acid.
A containment pit is the preferred rmethod of containing the liquid, since a pit usually will have a smaller surface area, and a lower rate of evolution of gas will result. A pit also can be covered more easily with foam or a sheet of impervious, compatible material Covering the liquid slows down the evolution of gas but does not stop it. Percolation of the liquid sulfur dioxide into the soil is greater in a pit than in a containment pond, so more contaminated soil may have to be removed.
IDENT1FICATI0N NUMBERS AND RATINGS
CAS
(Chemical Abstract Services)
7446-09-5
STCC
(Standard Transportation Commodity Code)
4904290
RTECS
(Registry of Toxic Effects of Chemical Substances)
WS4550000
UN/NA
(United Nations/North America)
1079
CHRIS
(Chemical Hazard Response Information System)
SFD
DOT
(U.S. Department of Transportation)
Nonflammable Gas
NFPA 704 Rating
2–0-0
IMO
(International Maritime Organization)
Poison Gas, 2.3
If the proper equipment is available fairly rapidly, the liquefied gas may be pumped out of the containment pond or pit into secure containers. However, the higher the ambient temperature, the more likely it is that all the liquid will vaporize.
If liquid sulfur dioxide reaches a waterway, it will sink in the water (because of its specific gravity of 1.436) and boil, forming sulfurous acid. If the waterway is fast-moving and the volume of liquefied gas is not large, no great harm should occur since the acid will be diluted fairly rapidly. Any gas released from the waterway will flow along the surface of the water, contained by the banks of the river or stream.
If possible, contaminated water should be diverted into low-lying areas, where the sulfur dioxide may be removed from the water with sparging techniques. If all the liquid has boiled away and the gas has dissolved in water, the resulting acidic solution may be neutralized by adding sodium bicarbonate (baking soda), sodium carbonate (baking powder), or calcium carbonate (ground limestone).
In any event, notify all downstream users of the water. ITiere is some chance that a large volume of the liquefied gas may be concentrated in a small volume of water, producing a more highly concentrated acid. Although sulfurous acid is in no way as dangerous as sulfuric acid, certain industrial equipment (boilers, machines that must be cooled by the water) may be harmed by the contaminated water.
The liquefied gas must be prevented from entering sewers, since sewers contain water—in which the sulfur dioxide will dissolve. Large amounts of liquefied gas entering the sewer evolves large amounts of gaseous sulfur dioxide, which tend to flow along the sewer system. The movement of a poisonous gas through the sewer system can cause damage to humans, including those at the sewage treatment plant. So alert all downstream treaters of the sewage to the possible arrival of contaminated water and toxic gas.
If the release occurs in an uninhabited area and no life or property is threatened, action on the part of emergency responders may not be necessary. The environment would be saved some contamination by containment efforts, but a release in open country may simply require the notification of environmental authorities. The authorities will determine how much contaminated soil salvage or cleanup firms must remove. They also will monitor waterways to determine when the water is considered safe.
FIRE SCENARIO
Since sulfur dioxide is nonflammable, gas releases are not subject to ignition. Indeed, if the gas is released ^ near a fire and upwind, it may act as a fire extinguishing agent. However,” the main hazard would be overpressurization of a gas container by radiation from a fire or direct flame impingement. Such rise in pressure imight cause the catastrophic failure of the container, releasing toxic gas and chunks of metal.
Containers of sulfur dioxide, just as containers of any other gas (pressurized or liquefied), must be kept cool if exposed to excessive heat by the application of as much water as possible from as far away as possible. Since some references call for evacuation of a 2,500-feet area around a large container, the water may need to be applied by unmanned monitors. Under no circumstances should a firefighter allow himself to be caught between a fire and exposed containers of gas.
Once the fire is extinguished, exercise care around containers exposed to the heat that remained intact.* These containers may have been weakened to the point that a slight impact may cause them to rupture violently. The odds are slight that any ,. containers still may contain gas, but the conservative approach is the sat-* est: Let the experts handle the cleanup and salvage.
Any water used to cool sulfur dioxide tanks that may have been venting is not likely to be contaminated by the gas, since all gases are more soluble inr cold water than in hot water. If any^ gas did dissolve in the water, the heat of the fire would warm up the contaminated water and drive out any dissolved gas.
FIRST AID
For inhalation, remove the victim to fresh air. If the victim has stopped* breathing or breathing has become difficult, administer artificial respiration (mouth-to-mouth resuscitation may expose the provider of first aid to »the material in the victim’s mouth or vomit). Provide medical attention immediately.
SYNONYMS
bisulfite
fermenicide liquid
fermenicide powder
sulphur dioxide
sulphur oxide
sulfurous acid anhydride
suiphurous acid anhydride
sulfurous anhydride
sulphurous anhydride
sulfurous oxide
sulphurous oxide
sulfur oxide
For ingestion, if the victim is conscious, administer large quantities of ‘water or milk. Do not attempt to • induce vomiting. Never try to force an unconscious person to drink anything 6r vomit. However, if vomiting occurs naturally, administer more water or ^milk. Call for immediate medical atr tention while making sure the victim is warm and comfortable.
For skin contact, remove all contaminated clothing and wash all affected body areas with large amounts of ^water. Medical attention is necessary if irritation of the skin persists after ^washing.
For eye contact, flush the eyes immediately with large amounts of water for 15 minutes, occasionally lifting the eyelids. Provide medical attention immediately.
PROTECTIVE CLOTHING AND EQUIPMENT
Choose protective clothing and equipment to prevent contact of liquid or gaseous sulfur dioxide with the eyes, skin, and respiratory system. ♦Frostbite may occur when skin contacts liquid sulfur dioxide. Select splashproof chemical goggles and a face shield for eye protection and use positive-pressure, self-contained ^breathing apparatus. Rubber boots, igloves, and aprons and other impervious clothing offer protection
