CHEMICAL DATA NOTEBOOK SERIES #31 Acetic Acid
HAZARDOUS MATERIALS
ACETIC ACID is a combustible, corrosive, irritating, clear, colorless liquid with a sour, pungent, vinegar-like odor. Glacial acetic acid is the pure form of the acid, being 99.8% pure with 0.2% water, but water solutions of the acid are common in shipping. Acetic acid is used to manufacture antibiotics, dyes, fibers, hormones, insecticides, nylon, pharmaceuticals, photographic chemicals, other plastics, and rubber, and it is used as a food additive. It is a stable chemical, but will react with strong oxidizers, strong caustics, and various other chemicals, including acetaldehyde, ethylene diamine, ethylene inline, phosphorus trichloride, and xylene. It is corrosive to most metals (including stainless steel) and will attack most plastics and rubber.
The acid’s chemical formula is CHjCOOH, and its structural formula is
PROPERTIES
Acetic acid has a flash point of 103°F, an ignition temperature of 800°F, and a flammable range of 4.0 to 19 9 percent. It has a specific gravity of 1.051, a molecular weight of 60, and a vapor density of 2.07. It boils at 244.2°F, freezes at 62.1°F. is soluble in water, and does not react with water.
HAZARDS
Acetic acid (glacial) is very corrosive to human tissue. It is also corrosive to metals and some polymers, but is more corrosive to metals when somewhat diluted with water than w hen pure. This property can present a hazard if dilution is selected as a mitigation technique and there are metals in contact with the concentrated acid. As water is added, the acid may begin to attack the metal, releasing explosive hydrogen.
Acetic acid is an organic acid, and therefore does not ionize to any great degree. The degree of ionization determines the strength of an acid, and although pure (glacial) acetic acid is of a high concentration and is corrosive, it is not classified as a strong acid, as are inorganic acids such as sulfuric, nitric, and hydrochloric acids.
Its flash point of 103°F takes it just over the limit for flammable liquids and gives it its classification as a combustible liquid. The implication is that the liquid must be warmed to 103°F before enough vapors are present to form an ignitable mixture, and this gives a margin of safety. How ever, this temperature is easily reached in industrial operations, warehouses that aren’t air-conditioned, and containers exposed to the sun during hot weather. The fact that it is an acid may also lull emergency responders into the misconception that acids do not burn. Indeed, acetic acid is an organic acid, and all organic acids will burn. Some are combustible solids and some are combustible liquids, but they are all organic compounds, and all organic compounds will burn.
Containers exposed to excessive heat can produce vapors sufficient to stress those containers to the breaking point. Containers that rupture violently when exposed to flame will produce BLEVElike explosions, with a fireball and burning liquid spewing forth.
Acetic acid’s threshold odor concentration is reported to be near 0.2 ppm. Its STEL is 15 ppm and its TLV-TWA is 10 ppm. Contact with concentrated acid (50% or more acid) will cause severe, permanent eye injury; very dilute solutions with 4% to 10% acid, such as vinegar, will cause some injury and considerable pain. Contact with concentrated acid will cause severe skin burns, with less injury caused by more dilute solutions.
The vapors of acetic acid are very irritating to the respiratory system. High concentrations of vapor will cause chest pain, coughing, nausea, and vomiting. Delayed effects may cause pulmonary edema and bronchopneumonia.
Ingestion of the concentrated acid can result in severe injury to the esophagus or death due to shock or other reactions. It is moderately toxic in its concentrated form. Ingestion of dilute solutions is relatively harmless, as in the vinegar used in salads.
SPILL SCENARIO: NO FIRE
As in the case of any flammable or combustible liquid spill, all ignition sources must be eliminated and approach must be made from upwind. Contact with the liquid must be avoided, and vapors must not be breathed.
The liquid must be prevented from entering sewers or waterways. Diking of catch basins to prevent sewer entry and damming of low-lying areas to prevent waterway entry must be considered. The proper environmental authorities must be notified immediately of the release.
It is advisable to contain the spilled liquid to prevent its movement and the subsequent spread of contamination. Containment dikes may be built by using sand, clay, soil, or other absorbent materials. Trenches may be dug to lead the liquid from the spill to the containment area. Containment pits may be dug if equipment is available. In each situation, soil contamination may increase from the liquid flowing through trenches or being contaminated in a pit.
Once the material is contained, no other action may be necessary until a professional salvage crew arrives. Production of acetic acid vapors from the spilled liquid should not pose a serious problem because of its low vapor pressure and high boiling points. Both properties indicate low vapor productions. However, because human tolerance for the vapors may be only 50 ppm (with higher concentration causing severe respiratory’ irritation to exposed persons), evacuation of the immediate area might be considered. The vapor density of 2.07 means that whatever vapors are generated will hug the ground, and these will flowalong the ground and accumulate in low’ or confined areas.
The warmer the day—and subsequently, the higher the temperature of the liquid —the more vapors will be generated. Control of these vapors can be gained by the use of water spray or fog. which will dissolve the vapors out of the air. Dilute solutions of acetic acid will be created by this procedure, and the runoff must be contained. Any spray or fog entering a containment pond or pit will add to the volume of liquid contained (while diluting it), and dikes may have to be reinforced.
The contained liquid may be pumped or vacuumed into containers using pumps and other equipment compatible with the acid. Secure metal containers for acetic acid are usually constructed of aluminum. After vacuuming or pumping, the remaining liquid can be absorbed by the addition of soil, sand, clay, fly ash, cement powder, or any other available sorbent. This technique can also be used on very small spills.
SYNONYMS
acetic acid, glacial ethylic acid
acetic acid, aqueous solution methane carboxylic acid
ethanoic acid vinegar acid
glacial acetic acid
IDENTIFICATION NUMBERS AND RATINGS
CAS
(Chemical Abstract Service)
64-19*7
RTECS
(Registry’ of Toxic Effects of Chemical Substances)
AF1225000
NFPA 704 rating
(National Fire Protection Association)
2-2-1
CHRIS
(Chemical Hazard Response Information System)
AAC
UN/NA
(United Nations/North America)
2789—glacial acetic acid (or as low as 80% concentration)
2790—solutions more than 10% acid concentration but less than 80% 1842—solutions less than 10% concentration
STCC
(Standard Transportation Commodity Code)
4931303 (glacial acetic acid)
4931401 (acetic acid, aqueous solution)
DOT
(Department of Transportation)
Corrosive
IMO
(International Maritime Organization)
3.3. corrosive
HAZARDOUS MATERIALS
ACETIC ACID
All salvage and cleanup work should be done by fully educated, trained, and equipped professionals. The absorbed material is still hazardous, and it must be disposed of in accordance with federal, state, and local regulations. Environmental authorities will advise as to the amount and proper disposition of contaminated soil that must be removed.
If vapors are being produced in quantities that are irritating or causing other discomfort, the surface of the contained liquid may be covered by an alcoholtype foam to slow the generation of such vapors. The foam may break down in a short time, and the blanket reestablished. This will increase the volume of the contained liquid.
Acetic acid may be neutralized by the addition of calcium oxide (lime). This will offset the corrosiveness of the acid and eliminate the production of vapors that will burn. However, calcium oxide is itself a very hazardous chemical, being highly water-reactive and very corrosive. Neutralization with lime should be carried out only by trained personnel wearing the proper personal protective clothing. The manufacturer of the acetic acid might recommend a less hazardous neutralization agent.
Dilution with water is another technique that will reduce the corrosiveness of the acid if enough water is added. This will raise the flash point and lower the vapor pressure of the liquid to levels where very few vapors are produced. Care must he taken to contain the additional volume of liquid. If metal contacts the spilled liquid, the corrosiveness of the acid toward the metal will increase at first as water is added, and then will decrease as the acid solution is diluted further.
The removal of contaminated soil must be supervised by environmental authorities, and care must be taken to avoid corrosion of tools and equipment. Contamination may be deep as a result of the percolation of the acid into the soil.
If the acid enters a sewer or waterway, the sewage treatment facility and/or all downstream users must be notified immediately. If the volume of water is great and the spill is relatively small, the resulting solution will be weak, and the dilution will be rapid to the point that danger and potential harm have been eliminated in a short span of the waterway.
However, if a large volume of concentrated or glacial acetic acid enters a sewer or slow-moving, low-volume stream or creek, the concentration of the resulting solution will be high, and therefore hazardous. If possible, the waterway should be dammed or diked, or the water otherwise diverted into an area from which it can be removed or treated. If the sewer’s flow can be diverted into a safe holding area, it should be directed there, and the acid either treated or removed. If the acid in the sewer is allowed to reach a treatment plant, severe damage can be done to metal piping and equipment, knocking out the plant and allowing raw sewage and concentrated acid to escape.
If water from a waterway has a large amount of concentrated acid and enters an industrial operation, an explosion is possible. It can happen if the water is heated to the point where it forces the acid to evaporate and vapors accumulate in concentrations within the flammable range. Corrosion damage can also be done to piping and equipment within the plant.
If the water can be contained, the acid can be removed by aeration or sparging, or air stripping.
Environmental authorities must monitor the movement of the acid, and they will determine if and when dilution by the water in a stream has eliminated all hazards. They must also be consulted if dilution in a sewer is to be accomplished by flushing. They can determine the volume of water required to reduce and/or eliminate hazards.
If the spill occurs in the winter or other periods of cold weather, there is a chance the liquid will be cooled below 62°F, and the acid will freeze. Once frozen, mitigation techniques can be reduced to securing the area and waiting for the salvage and clean-up crews to arrive. Those crews may choose to simply shovel the solid acid into secure containers while making sure that compatible tools and equipment are being used. However, do not count on a spill in cold weather: “Murphy’s Law” will not allow that to happen.
SPILL SCENARIO: FIRE
If containers of acetic acid are exposed to impinging flame or radiated heat from a fire, efforts should be made to cool the containers by applying water streams from as far away as practical with unmanned appliances. Catastrophic disintegration of the container is possible, with a resulting fireball and flooding of burning liquid. When large containers are involved, evacuation (and even withdrawal) may be necessary.
HAZAHDOIS MATERIALS.
ACETIC ACID
If the contained liquid catches fire, it can be extinguished by the application of alcohol foam or the use of a water spray or fog. For small spills, carbon dioxide or dry chemical may be used as extinguishing agents.
It is possible that reignition can occur if there is exposed metal contacting the liquid that has been heated by the fire. If the temperature of the metal is above 800°F, the acid will reignite, since this temperature is above the ignition temperature of the liquid. In dilute solutions, however, reignition will probably not occur because of lack of fuel. This is because when the material is in its pure or anhydrous form (no water present) the molecules of the compound are touching each other. Any energy applied to the compound will be absorbed by those molecules, and they will begin to vibrate faster and faster until they escape the liquid phase (evaporation). This is how vapors build up to the lower flammable limit, the first concentration level of vapors in air at which ignition can occur. When dilution is used, the addition of water to a water-soluble material will spread out the molecules of the soluble to a great distance, and any energy (heat) applied to the solution will be absorbed by the water and the dissolved compound. This will keep the temperature of the solution lowenough to prevent any large buildup of vapors. The resulting air-vapor mixture is below the lower flammable limit (too lean), and therefore will not ignite.
GLOSSARY
Aeration—A process by which air is introduced into a liquid, either by bubbling the air through it or spraying the liquid into the air at normal pressures.
Air stripping—A process by which a material is pumped through an air chamber or sprayed into the open air at high pressure to remove contaminants.
Copolymer—A rubber or plastic material made by the co-polymerization of two monomers, like sty rene and butadiene to make styrene-butadiene rubber (or nitrile-butadiene rubber). Three monomers, like those in acrylonitrile-butadiene-styrene (ABS), make a terpolymer.
Concentration—The amount of one material dissolved in another. In an acid, it is the amount of acid dissolved in water.
Dilution—The addition of water (or other miscible liquid) to reduce the concentration of a hazardous material.
Inorganic acid —Usually called mineral acids, they are ionic in nature, and all contain the H+ ion.
Organic acid—A compound with hydrocarbon backbone plus the carboxyl group (-COOH).
Sparging—A process by which air or other gas is bubbled through a liquid, solid, or gas to remove a contaminant.
Strength— Referring to an acid, it is the degree to which the acid ionizes when dissolved in water. Inorganic acids are strong acids, while organic acids are weak acids.
PROTECTIVE CLOTHING
Clothing should be worn that will prevent all contact of the liquid or vapors with the skin and eyes. This includes face shields or splash-proof safety goggles. Gloves, boots, and impervious clothing should be made out of such materials as butyl rubber, chlorinated polyethylene, natural rubber, neoprene, nitrile rubber, polyethylene, polyurethane, polyvinyl chloride, and several copolymer and terpolymer rubber compounds. Positive-pressure, self-contained breathing apparatus should always be used for respiratory protection.
FIRST AID
For inhalation of the vapors, the victim must be removed to fresh air and kept quiet and warm. Administer artificial respiration if breathing becomes difficult or stops, being careful that the provider of first aid is not exposed to the chemical within the victim s lungs and/or vomit. Get medical attention at once.
For eye contact, the eyes must be immediately and continuously flushed with water for a minimum of fifteen minutes, occasionally lifting the eyelids. Get immediate medical attention.
For skin contact, all contaminated clothing should be immediately removed, and affected body areas should be w ashed w ith large volumes of water. Medical attention should be sought at once.
For ingestion, do not induce vomiting. Administer large quantities of water and seek immediate medical attention.
