Chemical Data Notebook Series: Acrylonitrile
FEATURES
HAZARDOUS MATERIALS
Chemical Data Notebook Series:
A crylonitrile is a flammable, colorless liquid with a mild to very pungent odor. It is used in many industries and therefore is shipped all over the country, usually in rail tank cars, but occasionally in tank trucks. In addition to being flammable, it has many other hazards. You must exercise caution in handling any incident involving this material.
Acrylonitrile (pronounced akcril-o-nigh-trial) is used to manufacture plastics, rubber, adhesives, fibers, and pesticides, among many other materials.
Identification
Acrylonitrile has many synonyms, including Acritet, Acrylon, acrylonitrile monomer, Carbacryl, cyanoethylene, ENT-54, Fumigrain, Miller’s Fumigrain, propene nitrile, 2-propenenitrile, RCRA Waste Number U009, TL 314, VCN, Ventox, and vinyl cyanide. Its UN/NA designation is 1093, its STCC (Standard Transportation Commodity Code) is 4906420, its CAS (Chemical Abstract Service) number is 107-13-1, and its RTECS (Registry of Toxic Effects of Chemical Substances) number is AT5250000. (The RTECS number is sometimes referred to as the NIOSH, or National Institute of Occupational Safety and Health, number). The U.S. Department of Transportation classifies it as a flammable liquid, and the International Maritime Organization classifies it as 3.1, flammable liquid. Its NFPA classification is 4-3-2.
Properties
Acrylonitrile is somewhat soluble in water, and with a specific gravity of 0.806, it will float on water. It boils at 171° F and freezes at -117° F. Its molecular weight is 53, which makes its vapor density 1.83. (You can calculate the vapor density of any liquid or gas by dividing its molecular weight by 29, which is the average molecular weight of air.) This vapor density of 1.83 means the vapors of acrylonitrile will sink in air, flow along the ground, and accumulate in low spots.
Its flash point of 30° F means that most of the time the liquid will be producing enough vapors to form an ignitable mixture with the air. Coupled with its vapor density, this means that the vapors will flow along the ground (or waterway) until they find a suitable ignition source and will flash back to the origin of the material.
Acrylonitrile’s ignition temperature of 898° F can be reached by any common ignition source, all of which must be eliminated in case of an accidental release. Its flammable range of 3%-17% means that the lower flammable limit of 3% will be reached quickly on warm days (or in a warm structure or enclosure) and that any stream or accumulation of vapors will almost never be too rich.
Hazards
Acrylonitrile is corrosive to copper, any alloy of copper, and aluminum. It is not water-reactive, and it is stable when its tendency to polymerize is inhibited by the addition of a chemical stabilizer. It is reactive with ammonia, strong acids and bases, and amines.
The molecular formula for acrylonitrile is CH2CHCN. Its structural formula is:
H H
I I
c = c
I i
H C = N
This configuration shows that the feedstock for the manufacture of acrylonitrile is ethylene, and a cyanide radical has been substituted for one of the hydrogens in the compound. The presence of this cyanide radical is what makes acrylonitrile a very toxic material, as evidenced by the “4” in the blue health quadrant of the NFPA 704M marking system. It is toxic by all routes of entry into the body (ingestion, inhalation, absorption through the skin, and entry through a wound).
H H
I I
C = C i i
H H
Its TLV-TWA (Threshold Limit Value-Time Weighted Average) is 2 parts per million for skin contact. Of course, contact with the liquid should be avoided at all times, and when acrylonitrile is present at levels above 2 ppm, all emergency responders must wear the proper protection.
The major health hazard is from inhalation of the vapors, but prolonged skin contact must be avoided, since, based on long-term exposure to animals, acrylonitrile is a suspected carcinogen. Symptoms of exposure to acrylonitrile vapors include shallow breathing, nausea and vomiting, weakness, flushing of the face, headaches, and eye irritation leading to sensitivity to light. High concentrations of acrylonitrile lead to asphyxiation and death. Absorption through the skin, as well as ingestion, may also be fatal.
Since acrylonitrile is a monomer, an additional hazard is runaway (or violent) polymerization. The polymerization reaction is exothermic; that is, heat is liberated during the reaction. If the polymerization is uncontrolled, the entire mass will be polymerized at once, with all the heat energy being released at once, causing an explosion resembling a BLEVE (boiling liquid, expanding vapor explosion). This reaction is controlled during transportation by the use of a chemical stabilizer until the monomer is placed in a reactor vessel. Once in the reactor, the rate of reaction can be controlled by controlling the heat, pressure, and initiator used. (Note: A controlled reaction is one in which relatively small amounts of the monomer are polymerized slowly in a proper container, with the liberated heat being carried away systematically.)
Accidental releases
Whenever acrylonitrile is spilled or otherwise released, the primary concern is over explosions, fire, and the toxic nature of the vapors.
If the inhibitor used in the monomer to stabilize it is allowed to escape from the acrylonitrile (which it might do in situations where it is no longer under pressure, as in a spill), runaway polymerization must be considered as a possibility. There may be considerable agitation and boiling of the liquid if it begins to polymerize. If it doesn’t, attention must be paid to the generation of flammable and toxic vapors.
Approach must always be from upwind, and evacuation downwind must always be considered. The vapors will be hanging close to the ground, unless they are heated. These vapors will flow (gases, vapors, and fumes are fluids) along low spots in the ground, and if there is no wind in the area, the vapors may accumulate in such low spots. These vapors will also flow into open basement windows, causing dangerous amounts to accumulate.
Before entering any groundlevel enclosure, check for the presence of these flammable (actually explosive) vapors. As a matter of fact, the progress of such vapors may be followed by gas detection equipment that is used specifically for acrylonitrile.
If the release is a leak from a large container that is being stressed by impinging flame or radiant heat, the possibility of a BLEVE must be added to that of instantaneous, violent polymerization. Of course, even if the container is not leaking, but is being stressed by heat in one form or another, the threat of explosion (violent rupture) of the container is a possibility. Evacuation before an anticipated BLEVE must be at a minimum of one-half mile (farther downwind, if there is a leak).
If vapors escaping through the pressure relief valve or a leak are ignited, they should not be extinguished until the flow of fuel can be stopped. In any case, it may be wiser to let a toxic material like acrylonitrile burn rather than spread to a populated area. Deliberate burning is a strategy that must be considered in many incidents, especially when a toxic material is involved. However, in reaching a decision, the incident commander must consider the consequences of a deliberate burn, including property damage (which, of course, is secondary to the threat to human life).
Containment
Where a large spill must be handled, you must use standard procedures for containing liquids. You can use soil, sand, clay, and other materials to build a dike to create a containment pond. Evaporation of acrylonitrile will produce flammable and toxic vapors, and the rate of evaporation depends on the surface area of the liquid—that is, the larger the surface of the containment pond, the faster the acrylonitrile will evaporate. So it may be better to dig a containment pit, where the same volume of liquid may be held while presenting a smaller surface area to the atmosphere.
In any event, containment is a strategy used to prevent the spread of the released liquid and to keep it from contaminating sewers and waterways. Once it’s contained, you should turn your attention to reducing evaporation to minimize production of vapors.
Alcohol-type foams may be used to cover the surface of the liquid to reduce evaporation. Because the foam will break down in a relatively short time, you might have to apply the foams continuously. If a containment pit is dug, it may be possible to cover the surface with a tarp or other cover, rather than applying foam.
As part of mitigating the incident, obtain an approved, empty container (tank truck, tank car, or other suitable container). The product may be pumped from the containment pit into the secure container. All equipment used must be compatible with the acrylonitrile, and any motors driving the pumps must be explosionproof.
If foam is used, it may contaminate the product, as will any soil or other diking material. Also, all soil and diking material that was used and that came into contact with the product will have to be removed and disposed of in the proper manner (that is, following all federal, state, and local regulations). If qualified contractors are available, emergency responders probably should not be involved in the cleanup. Even if qualified independent contractors are not available, it is never a good idea for emergency responders to be involved in the cleanup. The danger of exposure during the incident is high enough, and few, if any, emergency responders are trained to clean up hazardous materials releases. The responsibility for cleanup lies with the shipper and/or owner of the material.
Once the acrylonitrile has been collected, instead of holding it for loading into secure containers, it may be absorbed by some other material, such as soil, clay, sand, sawdust, peat moss, fly ash, cement powder, or some commercial absorbent (assuming there is not an overwhelming amount of acrylonitrile and that there is enough of the absorbent available). Once absorbed, the contaminated absorbent will have some of the more dangerous properties of the spilled product. That is, the soil or clay (or other material) used to soak up the acrylonitrile will release flammable and toxic vapors unless it is confined in airtight containers. Just because the liquid no longer exists in a pool or pond doesn’t mean it is gone and/or is now harmless. All the rules for contact with acrylonitrile must be followed when you are handling contaminated sorbents (this also applies to adsorbents, which will be mentioned later) as well as the liquid.
Preventing water contamination
In addition to disposal methods, the proper environmental authorities (who must be alerted whenever any hazardous material is released) should be consulted to avoid possible groundwater contamination. With this in mind, it might be better for you to use a shallow containment pond rather than a deep containment pit. You may also consider using trenches and other excavations, always keeping groundwater contamination in mind.
The product must not be allowed to enter into sewers and waterways. If contaminated water downstream of an acrylonitrile incident is taken into an industrial process or any enclosed structure where an ignition source may be present, an explosion is possible. Entry into a sewer poses another explosion problem, particularly with a material with such a wide flammable range.
Dikes built in front of catch basins and low-lying ground leading to a waterway are necessary to prevent such occurrences.
If acrylonitrile does enter a waterway or sewer, all downstream users must be notified immediately; don’t forget sewage treatment plants. Since acrylonitrile is somewhat soluble in water, the product, in a stream of other moving water, will be dissolving in the water as the product and water are moving downstream. The product can be forced out of the water by agitation or heating, such as entry into an intake pipe leading into an industrial operation or some other use. If possible, all contaminated water should be diverted to a large containment area. Here, the water may be treated for safe removal of the product by the addition of an adsorbent or the use of aeration.
Adsorption may be contrasted with absorption in the manner in which the product is “captured” by the additive. Absorption is when a material actually penetrates the additive and “soaks” it, like water does to a paper or cloth towel. The absorbent material may then be taken to a secure container and deposited, or it may be physically “squeezed” in one manner or another to force out the absorbed product. In this manner, the absorbent may be used again.
Adsorption is when a material adheres (or “sticks”) to the outside of the adsorbent and is held there by some physical or chemical force. The contaminated adsorbent must then be disposed of or treated in some manner to get the contaminant to leave the adsorbing material.
Either method may be used to handle a spill. Absorbents usually are used to “soak up” a spilled product on the ground or floating on the water, while an adsorbent may be used to remove gases, vapors, and fumes from the air or to remove dissolved material from water.
Aeration is a technique whereby dissolved fluids may be removed from water or other solvents by agitation. The agitation is usually accomplished by bubbling air through the solvent (water, in this case). Agitation may also be accomplished by disturbing the water by causing it to go over waterfalls, stirring it vigorously, or pumping it into the air and letting it fall back to the surface of the water. With any aeration technique, vapors of the contaminant will be released into the air, and care must be taken to limit exposure and to prevent explosive accumulations of vapors.
All contaminated sorbents must now be disposed of by qualified agents according to all levels of regulation. This must also include all contaminated soil contacted by the acrylonitrile, as well as any contaminated product that may have been collected. It is always a good procedure for emergency responders to refrain from cleanup unless they have been properly educated, trained, and equipped to do the job.
First aid
The inhalation of acrylonitrile will produce effects that resemble poisoning by hydrogen cyanide. However, those effects may be delayed several hours. Death can occur when a person is subjected to levels as low as 400 ppm for four hours, and higher concentrations can be lethal in less time.
Glossary
BLEVE—Boiling liquid, expanding vapor explosion.
Initiator—A chemical added to a monomer that will overcome the stabilizer to allow the polymerization reaction to begin.
Monomer—A “tiny” molecule that has the unique chemical property of being able to react with itself to form a polymer.
Polymer—A “giant” molecule made up of thousands of monomer molecules that have reacted with themselves.
Polymerization—The chemical process in which monomers react with themselves to form polymers.
Stabilizer—A chemical added to a monomer to prevent polymerization. May also be called an inhibitor.
Acrylonitrile is highly toxic when it is inhaled, so attention must be paid immediately to anyone overcome by vapors. Fresh air and artificial respiration must be available at once. Procedures for hydrogen cyanide poisoning are recommended, including the administration of the vapors of amyl nitrate for 15 seconds. This must be repeated every 15 seconds for five minutes. After five minutes, use a fresh pearl of amyl nitrate. In the meantime, request emergency medical attention. The amyl nitrate treatment must continue for at least four pearls.
Acrylonitrile is also hazardous if ingested or if contact occurs with the skin. In case of ingestion, force the victim to drink large quantities of water, and then induce vomiting. If the victim is unconscious, administer amyl nitrate.
In case the victim has been splashed with acrylonitrile, remove the contaminated clothing at once, and use large amounts of water to wash the body where contact was made. If the liquid comes in contact with the eyes, flush them with water for a minimum of 15 minutes, occasionally raising the eyelid.
Any emergency medical facility receiving a victim who has been exposed to acrylonitrile must be alerted to the nature of the material. If for some reason the victim is still wearing the contaminated clothing or if it is still with him, the entire emergency room or trauma response capabilities of the medical facility may be shut down due to contamination by a toxic material.
Protective clothing
The protective clothing you select should prevent the liquid from reaching the eyes and skin. Anyone who will be entering a large spill area, who will be near any release where he may be splashed, or who must work in the product must wear a fully encapsulating suit with positive-pressure selfcontained breathing apparatus (SCBA). All material used to make the total encapsulating suit should be tested for resistance to acrylonitrile before use. Manufacturers of these suits will provide you with samples of the material for testing. Some manufacturers claim that suits made of butyl rubber, neoprene, nitrile-butadiene rubber, and polyethylene will protect against acrylonitrile. Protection is affected not only by the material used, but by the thickness of the material, integrity of the seams, concentration of the product contacted, and length of time of contact. In some cases, rubber gloves and boots, impervious turnout gear, and resistant face shields and goggles may be sufficient protective clothing for you to wear.
In any situation where unknown or high concentrations (anything above 100 ppm) are encountered, positive-pressure SCBA with full facepiece must be used. An umbilical air supply may also be used. NIOSH-approved respirators with the proper canisters or cartridges may be used in environments of lower concentrations. In any situation involving acrylonitrile, emergency responders must be protected against breathing the vapors and contact with the liquid.
Summary
The emergency responder must be protected against the hazards of acrylonitrile. Its low flash point means the danger of explosion is present at all normal temperatures. Its wide flammable range means the danger of explosion is present over a very wide area. Its low boiling point means the liquid will produce vapors that will endanger anyone who does not have breathing protection.
The vapors will produce poisoning similar to the ingestion of hydrogen cyanide, and the material itself is considered to be a suspected carcinogen.
Because acrylonitrile is a monomer, the possibility of uncontrolled, violent polymerization exists whenever the product is heated or when its container is leaking. This could produce a violent rupture of its container, with a resulting BLEVE-like explosion. And because acrylonitrile is a flammable liquid, all containers that carry it may rupture violently when they are heated.
