CHEMICAL DATA NOTEBOOK SERIES #106: CHLORINE DIOXIDE
BY FRANK L. FIRE
Chlorine dioxide is an oxidizing, unstable, reactive, toxic, irritating, yellowish-to-reddish gas with a pungent odor resembling chlorine or nitric acid. The U.S. Department of Transportation (DOT) forbids the transport of pure chlorine dioxide, which normally is diluted to less than 10 percent in a cold solution and shipped as a hydrate in its frozen form resembling orange-colored ice. It is used as a bleaching agent for beeswax, fats, flour, leather, oils, textiles, and wood pulp; in water-treatment plants; for treatment of swimming pools; as a biocide; and for odor control.
PROPERTIES
A powerful oxidizing agent, chlorine dioxide is nonflammable but will vigorously support combustion. In concentrations above 10 percent in air, however, it is highly unstable and may detonate. It has a vapor density of 2.32 and a molecular weight of 67.35. It freezes at -74°F, boils at 52°F, and is soluble in water. Its molecular formula is ClO2.
HAZARDS
The major hazard of chlorine dioxide (as it is commonly used) is oxidation. It is such a powerful oxidizer that it will cause ordinary combustible materials to burn vigorously and highly flammable materials to burn explosively. It is so hazardous that it is never transported in its pure state; it is generally produced on-site and used immediately. As it is produced, it is mixed with air or nitrogen so that the concentration never goes above 10 percent. It actually can be produced in the pure state if kept frozen solid, but doing this is too dangerous.
The standard rule of safety is that oxidizers never should be stored with materials that will burn. This rule usually is translated as, flammable or combustible materials may not be stored in the same area as the oxidizer. Since it is such a powerful oxidizer, it is recommended that chlorine dioxide not be stored in areas that have wooden floors or in containers with other stored materials made of wood, paper, cardboard, or other combustible materials. Contact even with dust in the area may make the chlorine dioxide so unstable that it would detonate.
Some references argue that chlorine dioxide is much more dangerous as an unstable material because of its propensity to detonate at concentrations above 10 percent. It also will react spontaneously and violently with such diverse chemicals as butadiene, carbon monoxide, difluoramine, ethane, ethylene, hydrogen, mercury, methane, phosphorus, propane, sugar, sulfur, and trifluoramine. Any contact with strong bases will stimulate decomposition. It reacts slowly with water to form hydrochloric acid and chloric acid.
Its oxidizing power makes chlorine dioxide extremely reactive. Its use in 10-percent concentration is a safety factor, an effort to keep the reactivity of the material within safe limits. Its uses, mentioned above, all fall within the realm of bleaching and other oxidizing functions. Even at the 10-percent level, chlorine dioxide is so reactive that it is a very efficient bleaching agent, which accounts for its widespread use.
Chlorine dioxide may not be rated as a toxic gas since it is so widely used in industry, but exposure to it can cause death. Its TLV-TWA (threshold limit value-time weighted average) is 0.1 ppm (parts per million of air), its STEL (short-term exposure limit) is 0.3 ppm, and its IDLH (immediately dangerous to life and health) limit is 10 ppm. Detection by odor has been claimed to be as low as 0.1 ppm, but this number has been deemed to be incorrect. A more realistic odor detection level has been established as 9.4 ppm, nearly 100 times its TLV-TWA and 31 times its STEL. An occupational exposure of 19 ppm has been reported as fatal, but no time of exposure was reported in that case.
Acute exposure to concentrations above the TLV-TWA can cause breathing difficulties, bubbling sounds in the chest, coughing, headaches, nasal bleeding or discharge, and vomiting. Effects of chronic exposure include bronchitis, coughing, eye and throat irritation, headache, runny nose, and wheezing. The most serious symptom could be pulmonary edema, the filling of the lungs with fluid; victims can drown in their fluid. The edema may be delayed for several hours after exposure so that a victim may not seek medical attention since the other symptoms do not appear to be too serious. Chlorine dioxide is a greater danger to the lungs than chlorine.
Exposure to chlorine dioxide will irritate the eyes and cause a burning sensation and may cause one to see a halo around lights.
Exposing the skin to concentrated solutions of chlorine dioxide in water will irritate it. Injuries due to the ingestion of solutions have not been reported; ingestion of the pure product is unlikely since the harmful product is a gas.
Chlorine dioxide is undoubtedly corrosive in high concentrations, but controls over its production, transportation, storage, and use will preclude the presence of the material in concentrations greater than 10 percent. Direct contact with water solutions of chlorine dioxide will be corrosive to metals and human tissue.
NONFIRE RELEASE
Since chlorine dioxide usually is produced and used on-site and the U.S. Department of Transportation forbids its transportation by common carrier, it might be assumed that there are no accidents involving this material in transport. However, the material–dissolved in water, frozen, and usually identified as “chlorine dioxide hydrate, frozen”–is transported by private or contract motor carrier. If the temperature of the frozen hydrate reaches 30°F, the hydrate will begin to melt, and chlorine dioxide gas will be liberated.
Any incident involving chlorine dioxide is serious enough to activate the community`s emergency response plan. The material is so dangerous that even small releases can be very hazardous.
Emergency responders must approach the incident site with extreme caution. Even though chlorine dioxide is not flammable, the approach must be made from upwind and uphill. The gas can be toxic, and it will allow anything that burns to become explosive. An apparatus driving into a cloud of chlorine dioxide would be affected in the same way as it would if operating in an oxygen-rich atmosphere: The engine would race and the acids produced by its combustion (principally hydrochloric acid) might seriously corrode the engine.
Emergency responders must be especially careful during the early stages of the incident. It would be a mistake to assume that, because chlorine dioxide will not burn, the precautions usually taken for flammable liquids or gases are not needed. This attitude can be extremely dangerous to everyone within the area, since any ignition source may cause any fuel (remember that a fuel is anything that will burn) nearby to become a raging inferno.
When a substantial amount of chlorine dioxide is released, emergency responders must consider evacuation early in the operation. Chlorine dioxide`s vapor density of 2.32 means that the gas will sink to the ground and flow, following low spots in the terrain. If there is a consistently strong breeze, the gas may be effectively dispersed in the air, removing much of the danger to exposed personnel. However, attention must be paid to all closed-in areas, especially downwind. Concentrations of gas will cause respiratory problems for unprotected personnel, and contact of the gas with anything that will burn will produce a dangerous fire hazard. Should the chlorine dioxide mix with any flammable gases, an explosion almost certainly will occur, sometimes instantaneously.
If there is little or no breeze, the danger, of course, is much greater. Using a high-pressure water or fog spray can effectively disperse the chlorine dioxide. When these mitigation techniques are used, the runoff water must be confined to minimize the spread of contamination. In addition, some acid gases, caused by the reaction of chlorine dioxide with the water used, may evolve.
When attempting to plug a container from which chlorine dioxide gas is leaking, all working near the leak must be protected from all contact with the material and use the proper respiratory protection. No combustible or flammable material that will react with or be ignited by the chlorine dioxide must be nearby. The material used to plug the leak, of course, must be resistant to chlorine dioxide.
Should a water solution of chlorine dioxide be released on land, containment procedures used for other liquids–such as digging a pit, building dikes, or digging trenches–may be used, but diking material must be selected with care, since chlorine dioxide will cause all organic material to be very combustible. Sand or soil may be used as diking material. The chlorine dioxide solution may seep into the soil, spreading contamination. Usually, after an incident has ended, several inches (or feet) of contaminated soil may have to be removed–the amount of soil to be removed will be determined by the proper environmental authorities.
If the released solution has been contained, it may be reclaimed by the shipper, the manufacturer, or a professional salvage team by pumping or suctioning into secure containers. Under no circumstances should emergency responders be involved in salvage operations.
Once the material has been contained and salvage of the original material is not a consideration, adding water to the contained material will lessen its potency. The resulting dilute solution may pose special disposal problems; the environmental authorities will have to determine what must be disposed of and what can be released into the environment.
The solution must be prevented from entering sewer systems. Adding a powerful oxidizer to the organic matter and oxygen already present in the sewer brings together two legs of the fire triangle; an ignition source is all that is needed to produce an explosion. The high oxidizer content of the mixture in the sewer will not require much energy to produce a raging underground fire throughout the system. Notify all sewage treatment facilities at once should chlorine dioxide enter the system under any circumstances.
Every effort should be made to prevent chlorine dioxide solution from entering waterways; but should the liquid enter a lake, pond, river, or stream, immediately dilute the concentration of chlorine dioxide and immediately notify all downstream users of the water. Aquatic life at the point of entry may be in some immediate danger; the danger should decrease as dilution occurs.
In some cases, mixing activated charcoal in the contaminated water will cause adsorption of the chlorine dioxide onto the charcoal, which then can be screened out of the water and must be disposed of in the proper manner.
Some references recommend neutralization techniques but do not specify which agent to use. A qualified expert can recommend safe neutralization techniques, which might include absorption with fly ash or cement powder and adding caustic soda. As in any situation involving adding neutralizing chemicals to accidentally released substances, make sure you do not make the situation worse.
FIRE SCENARIO
Containers of chlorine dioxide exposed to the radiant heat of a fire or in actual contact with flames are likely to fail catastrophically if the internal pressure rises before the pressure-relief device (if any) can activate. In addition to the shrapnel created by an exploding chlorine dioxide container, the chlorine dioxide will rapidly intensify the fire.
If the chlorine dioxide is accidentally released near a fire, keep the gas from reaching the fire. Since it is a very powerful oxidizing agent, it will intensify the fire to the point where no ordinary firefighting effort will be able to control it. The reaction would be similar to that of adding pure oxygen to the fire.
If possible, cool the containers as much as possible by applying water with unmanned appliances from as far away as possible. If the containers are leaking, the runoff water must be contained. Under no circumstances should firefighters allow themselves to get between the fire and containers of chlorine dioxide.
If no life is threatened by the release of the chlorine dioxide and it is already intensifying the fire, do not attempt to fight the fire. Protecting exposures may be the only safe mitigation technique since the chlorine dioxide will rapidly oxidize the fuel in the fire. The incident commander must be aware that hydrogen chloride will be among the combustion products produced by fires oxidized by chlorine-containing oxidizers.
Chlorine dioxide`s contacting a chemical with which it has a hazardous reaction will worsen the fire substantially or cause it to behave in a manner that will surprise emergency responders. When large amounts of chlorine dioxide are released and stand a good chance of contacting other materials, as in a release in a manufacturing operation, it is important to know which additional chemicals or metals are nearby and might be contacted.
PROTECTIVE CLOTHING AND EQUIPMENT
Protective clothing is required whenever contact with chlorine dioxide is a possibility. The water solution or gas never should be allowed to contact the skin; impervious clothing must be used at all times. In all cases, protective equipment means positive- pressure self-contained breathing apparatus, full face shields, rubber boots and gloves, and appropriate clothing impervious to chlorine dioxide. Total encapsulating suits are required in all instances. Impervious materials are not specifically recommended for chlorine dioxide; the materials listed as resistant to chlorine–including butyl rubber, neoprene, nitrile rubber, Saranex® and Teflon®–may suffice for chlorine dioxide. Hazardous-materials response team officers should ask manufacturers of the suits and chlorine dioxide for their recommendations. Gas masks with chlorine cartridges or chlorine cartridge respirators with full face pieces may be satisfactory for low concentrations (25 ppm or less), but they should not be used if there is the slightest chance the concentration may be higher.
FIRST AID
Inhalation. If inhalation problems are severe, victims must get fresh air immediately, and artificial respiration should be administered if breathing has stopped. (Those applying artificial respiration should be beware of the chlorine in the victim`s airway.) Medical attention must be given as soon as possible.
Skin contact. If liquid has contacted the skin, remove all contaminated clothing and wash all affected body parts with large amounts of water. Immediate medical attention is needed.
Eye contact. Flush the eyes immediately for at least 20 minutes, lifting the eyelids occasionally. Immediate medical attention is needed.
Ingestion. Ingesting the liquefied gas should not be possible. n
SYNONYMS
Alcide
anthium dioxide
chlorine oxide
chlorine dioxide hydrate
Frozen:
chlorine(IV) dioxide
chlorine peroxide
chlorperoxyl
chloryl radical
Doxcide 50
IDENTIFICATION NUMBERS AND RATINGS
CAS
(Chemical Abstract Services)
10049-04-4
STCC
(Standard Transportation Commodity Code)
4918110
RTECS
(Registry of Toxic Effects of Chemical Substances)
F03000000
UN/NA
(United Nations/North America)
NA9191
RCRA
(Resource Conservation and Recovery Act)
no designation
CHRIS
(Chemical Hazard Response Information System)
no designation
DOT
(U.S. Department of Transportation)
oxidizer, 5.1
NFPA 704 Rating
(National Fire Protection Association)
3-4-3
IMO
(International Maritime Organization)
5.1, oxidizer
FRANK L. FIRE is the vice president of marketing for Americhem Inc. in Cuyahoga Falls, Ohio. He`s an instructor of hazardous-materials chemistry at the University of Akron as well as an adjunct instructor of haz mats at the National Fire Academy. Fire is the author of The Common Sense Approach to Hazardous Materials and an accompanying study guide, Combustibility of Plastics, and Chemical Data Notebook: A User`s Manual, published by Fire Engineering Books. He is an editorial advisory board member of Fire Engineering.
