Chromic Acid
HAZARDOUS MATERIALS
Chemical Data Notebook Series #23:
Responders to a chromic acid leak should see red—and not only because red to dark purple is the color of the material in both solid and liquefied form. The crystalline solid is a carcinogen, it’s corrosive to both human tissue and metals, and it reacts violently to many substances. It’s also deliquescent, meaning it will gradually dissolve by attracting and absorbing moisture from the air. It should be treated with the same extreme care as any other acid, even in its solid form.
Chromic acid is highly reactive with all reducing agents, flammable and combustible hydrocarbons and hydrocarbon derivatives, and reactive metals such as sodium and potassium. It reacts explosively with acetone, methyl alcohol, acetic acid, phosphorus, pyridine, potassium ferrecyanide, and sulfur. There’s a less violent reaction to many other substances.
Reactivity makes chromic acid valuable in industry. The material is used in applying chrome plating, cleaning metal, etching plastics, and stripping copper, as well as the manufacture of ceramic glazes, colored glass, electric batteries, and many chemicals. It’s shipped in bottles, cans, bags, and drums.
Chromic acid is stable, nonflammable, toxic, irritating, water-reactive, and oxidizing. As a solid, it’s dark red to purple. When dissolved in water, it forms a red chromic acid solution, the darkness of which depends on the amount of solid dissolved, and generates a tremendous amount of heat. The material melts at 385° F, decomposing as it melts. It has a molecular weight of 100 and a specific gravity of 2.7, and is very soluble in water.
The chemical formula is CrCO3 for the solid and H2Cr04 for the solution in water.
In either form, the material is a powerful oxidizer and is very corrosive to human tissue and most metals, but particularly to copper and brass. It will attack leather, cloth, and some plastics. There’s also a possibility of a spontaneous ignition reaction when the material contacts some plastics.
Contact of the dry material with any fuel or reducing agent is very dangerous, since it gives us a material that bums—or possibly explodes—with the addition of just a little bit of energy. If the solution is in contact with a fuel and dries out, or the water is somehow removed, the same incendiary or explosive situation may exist.
Chromic acid is a human carcinogen. It’s also toxic, with a threshold-limit value/time-weighted average (TLV/TWA) of 0.05 milligrams per cubic meter (mg/m3) and a short-term exposure limit (STEL) of 0.1 mg/m3. It’s toxic by all four methods of entry into the body: ingestion, inhalation, absorption through the skin, and entry through a wound.
Whenever solid chromic acid is exposed to fire or extreme heat, the material will decompose, liberating very toxic chromium fumes. This can build up pressure within a sealed container, which could then fail catastrophically. Should containers of chromic acid be threatened by fire or extreme heat, evacuation to a minimum of 2,000 feet away is required.
Nonfire release
If the solid material is released, it probably will be in the form of crystals or powder. Containing the acid with a covering made of material resistant to it will prevent it from being blown about by the wind or made wet by rain. Resistant materials may include polyvinyl chloride, nitrile rubber, polyethylene, and chlorinated polyethylene.
If powder and crystals do blow about, a high-pressure spray or fog may be used to remove this dust from the air. There may be some exothermic reaction as the dust contacts the water, producing enough heat to be dangerous, but this may be preferable to letting the dust cloud blow into populated areas where it can cause serious injury and property damage. The resulting runoff will be a dark red solution of chromic acid, and it must be contained and treated as if a spill of the liquid has occurred. Any water resulting from rain must be treated the same way.
It’s important not to allow any chemicals or combustible materials to come into contact with the solid chromic acid, since it may not be easy to determine whether a violent reaction may occur. In a mixed shipment inside a tractor trailer or some other container, first responders must be certain that the chromic acid containers haven’t released their contents before anyone enters the trailer.
Any possible mixture of solid chromic acid with an unknown chemical shouldn’t be disturbed in any fashion until the mixture has been identified. The slightest friction, such as stepping on the material or brushing or sweeping it into a pile, could cause a violent reaction. Once the material has been identified as one that’s not combustible or a reducing agent, the mixture may be swept up and shoveled into a secure container. Only tools and containers resistant to the acid can be used.
If it’s been determined that chromic acid crystals or powder have mixed with a material with which they may react violently, the area should be secured and evacuated. The manufacturer, shipper, and buyer of the product should all be notified at the time of the spill so they can arrange for the clean-up, which will be extremely hazardous. Of course, in any spill of the solid acid or its solution, the proper environmental agencies must be notified at once. These people will guide the professional clean-up firms in determining what contaminated material must be removed. If at all possible, fire departments and other first responders shouldn’t be involved in the cleanup of hazardous materials.
The spilled material must not be allowed to enter sewers or waterways. The solid acid is especially hazardous in a sewer because the sewer will contain organic, and thus combustible, material, and a thorough mixture will occur, which will be dangerous.
If entry into a waterway does occur, all downstream users must be notified immediately to prevent them from drawing contaminated water into their processes. If chromic acid has entered a sewer, the sewage treatment facility, if any, must be notified. If acid solution enters a sewer, it may be advantageous to add water to the same opening, in effect diluting the solution as it moves along in the water. This technique should be used only after consultations with sewage treatment personnel and U.S. Environmental Protection Agency officials.
Containment, through creation of a diked pond, should be considered if a solution of the acid is released. Diking materials should be of dry sand, clay, fly ash, or other nonorganic materials. Soil may be used only as a last resort, since it may be very high in organic content and could ignite when dried out. A containment pit may be dug, along with trenches, to lead the liquid to the pit. In any event, once the incident has ended, all contaminated soil or diking material will have to be removed in accordance with federal, state, and local regulations. Again, this clean-up should be done by either professional clean-up firms or the manufacturer, shipper, or buyer of the product.
Solutions of the acid may be pumped from the containment pond or pit into secure containers, using only compatible pumps, equipment, and containers. Or, if the containment pond or pit is big enough, water may be added to weaken the acid. After dilution, tests must be run on the remaining solution to be sure that it is indeed harmless, or at least harmless enough to handle safely.
Neutralization is another alternative. The typical neutralizing agents—calcium carbonate (crushed limestone) and sodium carbonate (baking soda)—may be used, but only after consultation with the manufacturer of the acid. Small amounts of the solution should be sampled, and each of these agents added to separate samples, to see if neutralization will occur safely.
Any soil that has been in contact with the solution—be it diking material, the bottom of a pond, or the bottom and sides of the trenches and containment pit—will be contaminated with chromic acid. All contaminated soil and other material must be removed and disposed of in accordance with federal, state, and local regulations.
Absorption may be used if there isn’t too much liquid, there’s enough absorbent material, and the operation can be carried out safely. If there’s a lot of the chromic acid solution, the pumping technique might be used until only a small amount is left. This remaining liquid might then be absorbed. Typical absorbents might include sand, clay, cement powder, fly ash, and soil that’s relatively free of organic material. The absorbent material should be added to the liquid slowly. The resultant mixture will contain chromic acid, which should be handled as the solid chromic acid would be.
Synonyms
Chromic anhydride Chromic trioxide, anhydrous
Chromic oxide Chromic (VI) acid
Chromic trioxide
Identification Numbers and Ratings
UN/NA
(United Nations/North America)
1463 for the solid 1755 for the solution
CAS
(Chemical Abstract Service)
7738-94-5
RTECS
(Registry of Toxic Effects of Chemical Substances)
GB2450000
STCC
(Standard Transportation Commodity Code)
Association of American Railroads,
Bureau of Explosives
4918510 for the solid 493026 for the solution
CHRIS
(Chemical Hazard Response Information System)
U.S. Coast Guard CMA
IMO
(International Maritime Organization)
5.1, oxidizing substance (for the solid)
8.0, corrosive (for the liquid)
National Fire Protection Association 704 rating
3-0-1-OX Y
U.S. Department of Transportation
Oxidizer
The acid solution will be very corrosive to metals. If the solution dries because the water has evaporated, the solid material will be left behind, and the hazards mentioned above must be contained.
Fire situations
Whenever chromic acid is exposed to a fire, it may generate highly toxic fumes. If a highly concentrated solution is exposed, the water will evaporate, leaving the solid acid behind. And if that’s exposed, the material will decompose upon reaching 385° F, producing toxic chromium fumes. This decomposition will yield a thick, foaming material that may produce steam explosions on contact with water.
Containers of liquid exposed to a fire’s radiant heat, or worse, impinging flame, will experience increasing pressure due to the formation of water vapor, and catastrophic failure of the container may occur. Pressure build-up might also occur in a container of solid chromic acid, because of the chromium fumes created as the acid decomposes.
If the solid material is out of its container and has mixed with anything that burns, the mixture may react violently if heated by a nearby fire.
If water must be used on the fire, remember to contain any of it that contacts and dissolves the solid chromic acid. There may be some liability problems for fire departments that know, or should have known, about the presence of different haz mats and still used fire suppression techniques that caused a new problem with the spread of the material. This is all the more reason for first responders to a haz-mat incident, or a fire where haz mats are present, to know how other materials may react during mitigation or suppression.
Protective equipment should prevent any contact of the material with the eyes and skin, and positive-pressure, self-contained breathing apparatus should be used to protect the respiratory system. Protective gear should be chosen on the basis of whether exposure will be to the solid material, which may produce airborne dusts, or to the acid solution. Rubber gloves and boots will offer protection, and if a total encapsulating suit is chosen, compatible materials may include chlorinated polyethylene, nitrile rubber, polyethylene, PVC, and Viton.
Total encapsulating suits should be tested for resistance to specific reactive chemicals, including chromic acid, since protection is a relative term. That is, many materials used in total encapsulating suits are accompanied by claims from the manufacturers concerning the protection they offer. However, protection depends on many variables, including the thickness of the suit material, the integrity of the seams, the concentration of the chemical to which the suit is exposed, the length of the exposure, the type of exposure (dust, fumes or vapors, immersion in liquid, and so on), the age of the suit, the number of times the suit has been exposed to chemicals, and the types of chemicals to which it has been exposed.
If at all possible, swatches of the material from which the suit is made (in the same thickness) should be obtained from the manufacturer. These may then be tested against specific chemicals far in advance of actual exposure to determine how the suit will react. A few of the untested swatches can be properly labeled, and then exposed over several incidents. These swatches should be cleaned and decontaminated after each use, just as the suits are, thus producing an ongoing test that might predict fabric failure before it actually occurs in an incident. This could prevent serious injuries.
First aid
If a person has swallowed chromic acid, large amounts of water should be administered immediately. Some references suggest inducing the victim to vomit, while others advise against it. Either way, immediate medical attention is mandatory.
Should solid chromic acid be inhaled, the victim must be removed to fresh air and kept warm and quiet. Artificial respiration should be administered if breathing has stopped or become difficult. However, mouth-to-mouth resuscitation may expose the rescuer to the acid present in the victim’s mouth, lungs, or vomit. Again, immediate medical attention should be sought.
If chromic acid has contacted a victim’s eyes, they should be flushed with water for at least 15 minutes, with occasional lifting of the eyelids.
For skin contact, all contaminated clothing must be removed, then all affected skin must be washed with large amounts of soap and water. ■
Correction: In the November 1987 issue of Fire Engineering, the Chemical Data Notebook Series article listed butadiene’s chemical formula as C4H4. The correct formula is C4H6.
Glossary
Anhydrous—Without water present.
Concentration—The amount of a substance dissolved in water.
Deliquescent—-The property of absorbing moisture until the material dissolves in the water it has absorbed.
Reducing agent—A substance that removes oxygen from a compound. Contrast with oxidizing agent, which is a substance that contains oxygen and gives it up readily.
