CHEMICAL DATA NOTEBOOK SERIES #64: ACETALDEHYDE BY FRANK L. FIRE
HAZARDOUS MATERIALS
Acetaldehyde is a flammable, polymerizing, toxic, irritating, volatile, colorless liquid with a penetrating fruity odor. An intermediate product of combustion of many hydrocarbons and hydrocarbon derivatives, it is a very valuable chemical used as a raw material in the manufacture of dyes, mirrors, perfumes, pesticides, pharmaceuticals, plastics, synthetic rubber, and other materials as well as other individual chemicals.
PROPERTIES
An extremely flammable liquid, acetaldehyde has the following properties: a flash point of — 4()°F, an ignition temperature of 347°F, a flammable range of 4 to 60 percent in air, a specific gravity of 0.78, a molecular weight of 44. a vapor density of 1.5, a boiling point of 69°F, and a freezing point of — 185.8°F. It is very solublcin water. Its molecular formula is CHy CHO; it also may appear as C>H,().
HAZARDS
Acetaldehyde’s primary hazard is as a flammable liquid; it has many properties that allow it to ignite very easily. The first dangerous property is its flash point of — 40°F. This means that at all temperatures of — 40°F and higher, acetaldehyde liquid generates vapors sufficient enough to form an ignitable mixture with the air near the surface of the liquid or container. With the exception of North Dakota and northern Minnesota, few other places in the contiguous 48 states experience temperatures that low during the winter. For all intents and purposes, therefore, any time acetaldehyde is exposed to the air, you can assume that sufficient vapors have been liberated to form an explosivecondition.
The only thing missing is the ignition source, since the definition of flash point implies that the vapors arcpresent within the flammable range (implied by the term “ignitable mixture”). The very low ignition temperature (347°F) is attainable by all common (and some uncommon) ignition sources. Uncommon ignition sources include heated metal, hot liquids (boiling point of 347°F or higher), and anything else capable of reaching this relatively low temperature.
Acetaldehyde’s very wide flammable range (4 to 60 percent) also adds to its flammability potential. After the lower flammable limit of 4 percent ol acetaldehyde vapors in air has been reached, it will be almost impossible to find a situation in which the upper flammable limit has been surpassed (that is. getting more than 60 percent acetaldehyde vapors in air) and the mixture is “too rich” to ignite.
A density of 1.5 means that the vapor will “hang together” for sometime and flow along lowspots in the terrain (vapors and gases are fluids, just like liquids). These vapors may accumulate in low places or confined spaces. Anyone entering such an area could be overcome by the vapors, and the very high upper flammable rangemakes it likely that the collected vapor will explode.
Because* of its very high volatility in liquid form, acetaldehyde always generates largeamounts of vapor, and its very low boiling point (3°F below room temperature) means that on a warm day (or in a warm storage area), the liquid is stored above its boiling point. A liquid evaporates fastest at its boiling point; if heated much higher, it vaporizes instantly when the pressure of the container is released—much as water “flashes” to steam when a car radiator or hose springs a leak.
ACETALDEHYDE
The very low boiling point also increases the chance of a BLEVE occurring if the container is subjected to heat. If the pressure rise inside the container occurs faster than the pressure-relief device (if one is present) can release the pressure, the container will fail catastrophically, resulting in vaporized (and liquid) product — probably accompanied by shrapnel from the failed container—being spewed in all directions. The heat source causing the temperature and pressure rises also could serve as the ignition source, and the vapors will explode. If the vapors do not ignite, chances are that they will flow along the ground until they find an ignition source. The vapors then wall ignite explosively and “flash” back to the source of the spill, spreading the fire rapidly.
Aside from its flammability, which is bad enough, acetaldehyde is capable of polymerizing (special “tiny” molecules react with themselves to form “giant” molecules called polymers). When contained in a special vessel called a reactor—and with temperature and pressure under control—the chemical reaction is a safe one. However, when it occurs outside the reactor and outside the control of the chemical engineer in charge of the process, a runaway polymerization usually results. When this occurs, enough heat usually is generated to volatilize the liquid, causing rise in pressure and the ultimate failure of the container. In this situation, the chemical reaction often generates enough heat to ignite the vapors, and the resulting explosion will resemble a BLEVE. The results of the BLEVE and the runaway polymerization are the same: an explosion and fire that will do damage and probably cause injuries and death.
TOXICITY
Considered moderately toxic, acetaldehyde has a TLV-TWA (threshold limit value-time weighted average) of 100 ppm (in air) over an eight-hour day and 40-hour week and a STEL (short-term exposure limit) of 150 ppm for 15 minutes. Inhaling the vapors produces symptoms that include headache, dizziness, drowsiness, nausea with vomiting, unconsciousness. and eventually death. A level of 200 ppm for 15 minutes (an amount above the STEL) can cause eye irritation in humans. Concentrations as high as 1.36 percent (well below the lower flammable limit) have killed laboratory animals. Acetaldehyde’s odor is so strong that it can be detected at levels as low as 0.01 ppm (or 10 parts per billion in air). Pulmonary edema may later result.
ACETALDEHYDE
On exposure to air. acetaldehyde may oxidize partially and form potentially explosive organic peroxides.
NONFIRE RELEASE
Any appreciable release of acetaldehyde should trigger the emergency response plan mandated by SARA (Superftind Amendments and Reauthorization Act) Title III. Through the local emergency response committee, a communitywide emergency plan should be in place. Environmental authorities, who will be part of the response effort, will offer advice on how to avoid or minimize damage to the environment and spreading contamination during the incident.
Emergency responders should realize that acetaldehyde generates tremendous amounts of explosive vapors very rapidly and should approach the incident ground as they would in the case of any other flammable liquid release. Consider evacuating at least 1,50() feet around the release and distances one-half to two miles downw ind. The evacuation area may be as large as two miles in radius if a tank, wagon, or rail car loaded with acetaldehyde is involved. Consider also whether the leak is liquid or vapors, the location of the incident, the population at risk, the potential environmental damage, the damage to vital community systems, and property damage.
IDENTIFICATION NUMBERS AND RATINGS
CAS
(Chemical Abstract Services)
75-07-0
STCC
(Standard Transportation Commodity Code)
4907210
RTECS
(Registry of Toxic Effects of Chemical Substances)
AB1925000
UN/NA
(United Nations/North America)
1089
CHRIS
(Chemical Hazards Response Information System)
AAD
RCRA
(Resource Conservation and Recovery Act)
U001
DOT
(U.S. Department of Transportation)
Flammable Liquid
NFPA 704 Rating
2-4-2
IMG
(International Maritime Organization)
Flammable Liquid. 3-1
Leaking liquid should be contained by building a dike around the spill using soil, sand, clay, commercial sorbents, or any other material that will prevent the spread of contamination. Emergency responders should attempt to keep the containment area as small as possible since a direct relationship exists between the surface of liquid exposed to the atmosphere and the amount of vapors generated. A containment pit—since it is dug deeper—has a smaller surface. If a pit is used, contaminated soil may be more difficult to remove. Nonsparking equipment and tools must be used.
Anything that covers the surface also reduces the vapors generated. A tarp or a plastic or rubber sheet may be used to cover the surface, and the manufacturers of foams should be consulted to see if their products will reduce vapors. Alcohol-type foams may be effective for reducing the evolution of vapors, but they may have to be regenerated from time to time.
Every effort must be made to keep acetaldehyde from entering a sewer system, pond. lake, or other waterway. Diking at manholes and catch basins should prevent entry into sewers, but if the product does enter the sewer system, acetaldehyde readily will dissolve in any water present. The movement of the water through the system will cause explosive vapors to be generated from the solution, and a very dangerous explosive situation will exist through much of the system. All sewage-treatment plants must be warned and ignition sources must be eliminated all along the route of the contantined sewer, especially at openings. The entire sewer system runs the risk of exploding.
SYNONYMS
acetic aldchvdc
akichyde
cthanal
ethyl aldehyde
Should acetaldehyde enter a pond or lake, it immediately will dissolve and spread through the water. The environmental authorities must be consulted to determine if the product has been diluted below the levels dangerous to aquatic life and water fowl or whether actions such as agitation and aeration techniques, which could include sparging (a process that bubbles air or another gas through a liquid, solid, or gas to remove a contaminant) and/or spraying, are needed. Again, the environmental authorities must determine if the contamination has been removed in that maaner.
Acetaldehyde reaching a stream or river will dissolve rather quickly. The volume of water, its rate of speed, and how much product has entered will affect the extent of contamination. Dilution occurs quickly in a large volume of water or in water that is moving rapidly. If the water is significantly agitated, however, the product will be expelled as a vapor. These heavier-than-air vapors could be contained by the waterway banks and become concentrated enough to form an explosive mixture. In any event, all downstream users of the water must be notified immediately.
If a large pool has formed—-or if the liquid has been contained in a pond or pit—vapors rising from the liquid may be dispersed downwind by sweeping actions of hoselines using high-pressure spray or fog patterns. All runoff w’ater from this technique should be contained.
If the containment pond or pit is large enough to hold a greater amount of liquid, adding water to the acetaldehyde w’ill dissolve it, dilute it, and reduce the evaporation—and therefore also the explosion hazard.
The manufacturer, shipper, and buyer of the acetaldehyde should be notified at once of a transportation accident involving their product. Under some circumstances, the product may be off-loaded from the involved container to a secure container. The product also may be suctioned from a containment pond or pit into a secure container. Adding cement powder, clay, fly ash, peat moss, sand, saw dust, soil, or some other material or commercial sorbent to any material left on the ground will help absorb it. Ilie resulting mixture should be handled as carefully as the pure product and must be disposed of in accordance with federal, state, and local regulations. Only professional salvage firms should handle cleanup.
FIRE SCENARIO
Applying alcohol foam, carbon dioxide, dry chemical, or high-pressure water spray or fog patterns may extinguish burning acetaldehyde; their effectiveness will depend on variables such as the amount involved in the fire, spill conditions, terrain, and weather. If acetaldehyde leaks from a container as a liquid or vapor, the flames should not be extinguished until the flow of fuel can be stopped. Extinguishing the burning pool of acetaldehyde may be a futile gesture, since the substance’s ignition temperature is so low that it can be reignited by almost any material heated by the just-extinguished fire, tiertainly, any piece of metal the flame contacts will be at a temperature above 347°F and serve as an ignition source. Reignition of a large pool of flammable liquid can happen explosively, and anyone moving in on the liquid after the fire has been extinguished could be severely injured or killed by the reignition.
ACETALDEHYDE
Containers heated or contacted by flames should be cooled by unmanned appliances from as far away as possible. The possibility of a HI.EVE (or, more rarely, a runaway polymerization) is very high when acetaldehyde is involved. Even after the fire has been extinguished, containers of acetaldehyde that have been heated severely —even though they did not fail —may be very dangerous.
At least one reference claims that burning acetaldehyde produces unusually toxic combustion products, so exposed people downwind may be in danger.
PROTECTIVE CLOTHING AND EQUIPMENT
Protective clothing and equipment must prevent contact of the liquid and vapors with the skin and eyes. Rubber gloves and boots, full face shields, and chemical splashproof safety goggles are required. Positive-pressure selfcontained breathing apparatus must be worn at all times when acetaldehyde vapors may be present. Some manufacturers of total encapsulating suits claim that suits made of nitrilebutadiene, butyl rubber, polyethylene, polyvinyl chloride, polyurethane, and styrene-butadiene rubber may provide adequate protection from acetaldehyde. One reference, however, lists butyl rubber as the only recommended protective material. Consult manufacturers of total encapsulating suits to determine whether the suits will protect the wearer from acetaldehyde—and for how long a period such protection will last.
FIRST AID
Inhalation. The victim should be moved to a fresh-air location, kept warm, and given artificial respiration if breathing has stopped or becomes labored. Emergency care givers should be aware that they could be exposed to the material in the victim’s lungs and/or vomit while administering artificial respiration.
Eye contact. Flush the eyes immediately for at least 1 5 minutes, lifting the eyelids occasionally. Summon immediate medical attention.
Skin contact. The affected areas of the body must be washed with large amounts of soap and water. If irritation continues after washing, summon medical attention. Skin contact can cause irritation, redness, and burns; prolonged or repeated contact can cause a rash.
Ingestion. If conscious, large quantities of water should be taken immediately; vomiting should be induced. An unconscious person should never be made to drink anything or to vomit. Summon immediate medical attention. Ingestion of the liquid can cause symptoms similar to those resulting from inhalation, as well as possible kidney damage.
