Chlorine
FEATURES
HAZARDOUS MATERIALS
Chemical Data Notebook Series:
According to an unreleased report by the U.S. Environmental Protection Agency (EPA) concerning hazardous material incidents from 1980 through 1985, chlorine caused more deaths and injuries than any other toxic chemical involved in these accidents. Out of some 6,928 incidents reviewed by the EPA, chlorine was involved in approximately 665 accidental releases and caused 135 deaths and nearly 1,500 injuries.
PROPERTIES AND APPEARANCE
Chlorine is a member of the family of elements known as halogens (other members are fluorine, bromine, iodine, and astatine, which is radioactive and very rare). A yellowish-greenish gas that is 2.45 times heavier than air and very slightly soluble in water, chlorine does not exist in the elemental form, but in molecular form. The chemical symbol for chlorine is Cl, but when it is generated, it exists as the diatomic molecule, Cl2.
Like many other gases, chlorine is usually liquified for transportation and storage. This is done for economic reasons, since you can get so much more material into a given volume as a liquid rather than as a gas or vapor. For instance, chlorine produces 457 cubic feet of gas for every cubic foot of liquid. This means, of course, that you can store or transport 457 times more chlorine as a liquid than as a gas.
Liquid chlorine (like the gas) has a greenish-yellow tint, and a specific gravity of 1.56 (as opposed to its vapor density of 2.45). Of course, whenever liquid chlorine is exposed to air, it begins to boil away since its boiling point is about -30°F.
The chemical properties of chlorine make it an oxidizer, a corrosive, and an irritant (as DOT might classify it) or toxic (as IMO classifies it with a 2.3 designation at the bottom of a DOT placard). All these features make chlorine a highly reactive material, which is the reason that chlorine is so important to industry, being used in the manufacture of a great variety of chemicals and materials, among which are bleaches, plastics, rubber, dyes and pigments, pulp, paper, refrigerant gases, fire extinguishing agents, disinfectants, and in the production and/or processing of innumerable specific organic and inorganic chemicals.
Chlorine may also be found in large quantities in water treatment and sewage treatment plants. Chlorinated hydrocarbons (which means that chlorine has been chemically attached to a hydrocarbon by substituting it for a hydrogen atom) are very valuable to industry as solvents, de-greasers, and other important commercial uses, so chlorine may be found in any industrial plant that manufactures these materials.
Chlorine has one synonym, bertholite, but may sometimes be referred to as molecular chlorine or liquid chlorine.
IDENTIFICATION
Chlorine containers can be identified by the use of the Department of Transportation (DOT) nonflammable gas placard with the UN designation 1017 in the center of the placard or next to the placard. Its Standard Transportation Commodity Code (STCC) number is 4904120, and its National Fire Protection Association (NFPA) rating (704) is 3-0-0-OXY. DOT required labels are non-flammable gas and poison.
HAZARDS
Chemical actions and reactions
Although chlorine does not burn, which is the reason for the DOT designation as a non-flammable gas, like oxygen, chlorine does support combustion. As a matter of fact, chlorine is almost as efficient an oxidizer as oxygen. This means that any ordinary combustible or very flammable material may become explosive when mixed with chlorine. Therefore, all combustible materials, particularly organic substances, and all powdered metals and many metal compounds must be kept separated from chlorine.
If chlorine is released anywhere near a fire incident, efforts must be made to keep the chlorine gas from reaching the fire. Since chlorine 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—similar to the addition of pure oxygen to the fire.
The fact that gaseous chlorine is so heavy (2.45 times as heavy as air) means that the gas “hangs together” and flows along the ground, seeking low spots in the terrain. Obviously, these areas are extremely dangerous because of the concentration of chlorine. This hazard can exist quite far from the initial incident, and, depending on the size of the release, evacuation distances downwind may have to be extended one to two miles or more.
An interesting method of chlorine detection in low-lying areas, and in basements or other confined areas into which chlorine might have flowed and become trapped because of its high vapor density, is the use of a rag soaked with ammonium hydroxide, tied to the end of a long pole. If this rag is waved around in an atmosphere containing chlorine, a white cloud will form wherever the rag contacts chlorine. However, although this detection method will warn of the presence of chlorine, it will not indicate the level of concentration.
If you suspect that chlorine is present, keep your mask on. The use of gas sampling and detection devices will accurately measure the presence of chlorine at levels that are very low, but still harmful.
Driving into a cloud of chlorine is dangerous to the vehicle as well as to the occupants. Being a strong oxidizer, the chlorine will support the combustion of gasoline or diesel fuel, and there can be severe damage (corrosion) to the engine if chlorine is pulled through with air, making the engine race as if at full throttle.
In addition to its oxidizing power, chlorine is a very strong corrosive, especially where large quantities come in contact with water. Chlorine will react with almost all metals at elevated temperatures, and some metals, like copper, may spontaneously ignite in the presence of chlorine.
Personal
Needless to say, chlorine is very corrosive to skin and eyes, and contact with the liquid or gas must be avoided at all costs.
If being an oxidizer and corrosive is not enough to make chlorine highly hazardous (and it is), it is also toxic when present in sufficient quantities. The TLV (threshold limit value) for chlorine is 1 ppm and the short-term exposure limit (STEL) is 3 ppm for 15 minutes. You should be able to detect the presence of chlorine around the 3 ppm level (perhaps even as low as 0.02 ppm) as a pungent, choking, irritating odor, described as acrid. It may also resemble the odor of household bleach (which contains chlorine).
Irritation of the eyes, mucous membranes, and respiratory tract may occur at concentrations between 3 ppm and 15 ppm. Exposures at 15 ppm will cause immediate irritation of the throat, while levels of 50 ppm are dangerous, often resulting in severe breathing difficulties, and exposure to chlorine concentrations of 1,000 ppm for even a very brief period may be fatal.
Since chlorine is so irritating, exposure to very high concentrations is rare, unless the exposed person is unable to leave the area. Initial irritation of eyes and the mucuous membrane of the nose and throat is followed by coughing and a constriction of the chest, accompanied by a feeling of suffocation and pain. Pulmonary edema follows in severe exposures.
Victims of severe inhalation problems must get fresh air immediately, artificial respiration if breathing has stopped, and medical attention as soon as possible. (For those applying artificial respiration, beware of the chlorine in the victim’s airways.)
For those victims who have contacted the liquid, all contaminated clothing must be removed, and all affected body parts must be washed with large amounts of water. Medical attention must be given immediately.
PROTECTIVE CLOTHING
Protective clothing is required if there is any possibility of contact with chlorine. This means wearing positive pressure self-contained breathing apparatus (SCBA), full faceshields, rubber boots, as well as gloves and clothing that is impervious to chlorine. Impervious materials include polyvinyl chloride, chlorinated polyethylene, Viton, and neoprene. Fully-encapsulating suits may be required in some instances.
Gas masks with chlorine cartridges or chlorine cartridge respirators with full facepieces are satisfactory for low concentrations (25 ppm or less), but should not be used if there is the slightest chance that the concentration may be higher.
HANDUNG
Spills
Remember that spilled/released liquid chlorine will be in an environment that is somewhat warmer than the chlorine itself, and this will promote boiling and rapid generation of chlorine gas. Be aware of the generation of this gaseous chlorine and the direction it will travel.
Glossary
Atom—The smallest part of an element that can still be identified as the element.
Bolling point—The temperature at which the vapor pressure of a liquid just equals atmospheric pressure.
Diatomic—Made up of two atoms, as in a diatomic molecule.
Element—A pure substance that cannot be broken down into simpler substances by chemical means.
Gas—A state of matter defined as a fluid with a vapor pressure of 40 psia at 100°F.
Molecule—A chemical combination of two or more atoms, either of the same or different elements. The smallest particle of a compound that can still be identified as the compound.
Specific gravity—The weight of a solid or liquid as compared to the weight of an equal volume of water.
STEL—Short-term exposure limit. The maximum amount of material to which a person may be exposed over a period of time without harmful effects.
TLV—Threshold limit value. The amount of a substance to which an average person in average health may be exposed in a 40-hour work week without harm. The values may be averaged over time, and the TLV may also be referred to as TWA or time weighted average.
Vapor density—The relative density of a vapor or gas as compared to dry air.
Vapor pressure—The pressure exerted by vapor on the sides of a container at equilibrium. Equilibrium is reached when the vapor pressure of the vapor in the container has stabilized.
Water fog may be used to direct the movement of gases and will even absorb some of them. In all cases, however, be careful that water is not added to the spill, since this will increase the generation of gases. Also be careful to account for runoff, as this will contaminate water supplies.
NOTE: Although chlorine is used to purify water, the amount that ends up in the drinking water supply is carefully controlled, and excessive amounts can be very harmful.
In the case of a spill on land, containment procedures used for other liquids may be utilized, even though chlorine will be rapidly evaporating since the ambient temperature will probably be above chlorine’s boiling point. These techniques include digging a pit, building dikes, or digging trenches. Sand or soil may be used as diking material. In each case, however, liquid chlorine 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.
If it is deemed necessary to retard the release of chlorine gas from the exposed liquid, a fluoroprotein foam or a special chlorine foam may be applied to the surface of the spill. This procedure should be considered only as a short-term solution, however, since the foam will break down and the generation of gases will resume.
If the release is the result of a ruptured container and no pit has been dug or no dike has been constructed, a corrosion-resistant pump may be used to pump the liquid back into the leaking container or into chlorine-resistant containers (made of plastic, glass, or the same metal as the original container). These are short-term solutions, producing semi-closed systems to hold the chlorine until an adequate/proper container can be secured.
Again, any exposed chlorine liquid will be boiling and generating chlorine gas, so anyone working on the containment procedure must be properly protected and evacuation downwind must be a prime consideration.
The use of chlorine kits is recommended by shippers to handle small leaks from various size chlorine containers. The kits, labeled A, B, and C, are for containers ranging from one ton to bulk storage railcars.
All efforts must be made to keep the liquid from entering a sewer or waterway, as this will cause the intimate mixing of organic material (fuel) with the liquid chlorine (oxidizer). All that is needed to complete the fire triangle is an energy/ ignition source, which, if found, can cause a spectacular underground explosion that could affect an entire city.
Entrance of liquid chlorine into a waterway will also cause serious problems to the water downstream. Care must be made to warn all users of the water, industrial as well as municipal. In all cases, the operators of the sewage treatment plant through which the contaminated water may pass must be notified.
In some cases, mixing activated charcoal into the contaminated water will cause adsorption of the chlorine onto the charcoal, which could then be removed from the water by screening it out. In every instance, however, notify water users downstream.
Neutralization
Some references call for neutralizing chlorine spills, but do not specify the proper neutralization agent. One possibility is absorption with fly ash or cement powder and the addition of caustic soda. As in any situation where chemicals will be added to accidentally released substances to neutralize them, care must be taken not to cause the situation to worsen.
When preplanning for the possibility of a chemical release, qualified experts should be consulted to determine safe neutralization techniques, and, if possible, retained on call in the event of an emergency.
Consideration should be given to trying to divert contaminated water until it can be properly heated to eliminate the chlorine. This may require damming and/or diking the waterway, and diverting the water through some landbased decontamination station. It may even be possible to divert the contaminated water through a sewage treatment plant, but permission must be obtained from the sewage plant operators before this tactic can be used.
SUMMARY
In any release, all emergency personnel must be aware of all the hazards presented by chlorine. Since chlorine boils at -30° F, that must be the maximum temperature of the liquid, and any water applied to it will be at least 63° warmer, causing an increase in the generation of gaseous chlorine. This will increase the intensity of the fire and the amount of toxic gases in the air.
Also be aware of the possibility of uninvolved chlorine containers exploding whenever they are subjected to extreme heat.
