CHEMICAL DATA NOTEBOOK SERIES #107: ETHYL ACRYLATE
BY FRANK L. FIRE
Editor`s note: The Chemical Abstract Services (CAS) number for sodium hydrosulfide in the May 1995 Chemical Data Notebook Series #105 (page 75) should be 16721-80-5.
Ethyl acrylate is a carcinogenic, flammable, polymerizable, toxic, irritating, colorless liquid with a sharp, nauseating odor. It is a monomer for one of the acrylic resins used in making adhesives, paint, paper, plastic films, and textiles and is becoming an increasingly popular chemical.
The term acrylic covers a wide family of plastics. In addition to polyethyl acrylate (formed by the polymerization of ethyl acrylate), other acrylic plastics include ethylene acrylic acid (EAA) copolymers; ethylene butyl acrylate; ethylene-ethyl acrylate (EEA); ethylene methacrylate; ethylene methacrylic acid copolymer; and, the most common, polymethyl methacrylate (PMMA). All monomers of thermoplastics are hazardous materials.
Ethyl acrylate has a flash point of 44°F, an explosive (flammable) range of 1.8 percent to 12.1 percent in air, an ignition temperature of 721°F, a specific gravity of 0.923, a molecular weight of 100, and a vapor density of 3.45. It boils at 211.3°F, freezes at -98°F, and is slightly soluble in water. Its chemical formula is CH2CHCOOC2H5.
Ethyl acrylate`s major hazard is flammability. Its flash point of 44°F means that at all ambient temperatures in industrial and warehouse conditions, ethyl acrylate will generate sufficient vapors to form an explosive mixture with the air near the surface of the liquid. Its ignition temperature of 721°F can be easily reached by all common ignition sources. Its explosive range is sufficiently wide that once the lower explosive limit is reached, it will be almost impossible to find concentrations above the upper explosive limit. The rather high vapor density of 3.45 means the vapors of ethyl acrylate are 3.45 times as heavy as air; consequently, vapors will drop to the ground, flow along lower areas in the terrain, and accumulate in these low spots. The heavy vapors also will accumulate in any confined areas they happen to enter. Since vapors are fluids, they will flow downhill if undisturbed by wind. “O`Brien`s Law” (which states that Murphy, as in “Murphy`s Law,” was an optimist) seems to cause all vapors of flammable and combustible liquids to move toward likely ignition sources. Once they reach an ignition source, the vapor/air mixture explodes, flashing back to the original vapor source.
Toxicity is another hazard of ethyl acrylate. Inhaling high concentrations can produce drowsiness; headache; narcosis; nausea; vomiting; and, under some circumstances, death. Ethyl acrylate has a TLV-TWA (threshold limit value-time weighted average) of five ppm (parts per million of air) and an STEL (short-term exposure limit) of 15 ppm. It is a suspected human carcinogen, and its vapors irritate the skin, eyes, nose, throat, and respiratory system.
Entering, without respiratory protection, low-lying areas or confined spaces that have an accumulation of ethyl acrylate can severely irritate the lungs and cause unconsciousness and death.
Used almost exclusively as a monomer, ethyl acrylate`s only reason for existing is to polymerize plastics. Polymerization is a process in which a relatively small molecule has the rare ability to react with itself to form a giant molecule called a “polymer.” When performed under the proper conditions–in a polymerization container (reactor or a closed vat) where the heat and pressure applied to the monomer are carefully controlled–this chemical reaction is very safe. Polymerization is an exothermic (heat is liberated) reaction, and the evolved heat must be systematically removed. When polymerization occurs outside the reactor, as in an accidental release, the evolved heat of reaction builds up so rapidly that the polymerization reaction quickly becomes out of control (a so-called “uncontrolled” or “runaway” polymerization). On some occasions, this uncontrolled chemical reaction produces an explosion that closely resembles a BLEVE (boiling-liquid, expanding-vapor explosion).
Uncontrolled polymerization can occur any time the monomer`s temperature rises rapidly, such as when a container being transported is subjected to the heat of the sun on a hot day. To prevent premature polymerization reaction, an inhibiting or stabilizing chemical is added to the monomer. As long as the inhibitor stays dissolved in the monomer, the monomer will resist the urge to react with itself and begin a runaway polymerization. However, if the temperature increases enough and the pressure over the liquid is released, the inhibitor may be forced out of the monomer. In a now unprotected condition, the monomer may begin to polymerize, producing heat as the reaction proceeds. As this evolved heat is absorbed by the remaining unreacted monomer, the polymerization reaction proceeds even faster, producing even more heat. Inhibitors used to prevent premature polymerization of ethyl acrylate include hydroquinone, hydroquinone methyl ether, and dimethyl tert-butylphenol.
An irrevocable law of chemistry states, as the temperature of a chemical reaction increases by 10°C (18°F), the speed of that chemical reaction doubles. As the material (in this case, a reactive monomer) continues to react and the temperature of the reactants continues to rise, the reaction and the release of heat speed up. Very rapidly, the chemical reaction increases its speed until the unreacted monomer explodes. For this reason, the polymerization reactor must be able to withstand certain pressures and remove the evolved heat as it is produced. This is also the reason emergency responders must be aware of the explosive hazards of monomers in general, including the temperatures and pressures to which the material has been exposed, and for how long. The emergency responder must realize the container (sometimes as large as a rail tank car) may ex-plode with deadly results.
Since ethyl acrylate is a monomer, it is inherently an unstable chemical. It reacts with strong acids, alkalis, and reducing agents and with oxidizers (including organic peroxides and any initiators for polymerization).
The release of an appreciable quantity of ethyl acrylate should activate the community`s emergency response plan. Since fire and explosion (a released vapor explosion as well as a BLEVE) are imminent once the material is released, the local fire department will almost always assume command of the incident, except where federal, state, or local law stipulates that another response organization is to command the incident.
Treat a release of ethyl acrylate as any other flammable liquid release: Approach always from upwind and uphill; eliminate all possible ignition sources, especially downwind and downhill; remove all nonessential personnel from the danger zone as soon as possible; and consider immediately evacuating the area surrounding the danger zone. The radius of evacuation depends on the size of the container, the amount of material pres-
ent, the local terrain, and present and forecast weather conditions.
The chemical and physical properties of ethyl acrylate must be considered when mitigating an incident. Knowing all these properties enables the responder to predict with some certainty what will occur under different sets of circumstances and can save many lives, including those of emergency responders.
Caution is needed when ethyl acrylate liquid has been released from its original container. Should it be contaminated by contact with any other material, it will become sensitized and ready to polymerize. Although this reaction is less dangerous if it occurs in the open instead of when the liquid is confined, enough heat will be generated to volatilize the liquid, increasing the amount of vapors present in the air so that they could ignite and explode. The source of ignition could be the heat energy released from the reaction itself as the reaction speed increases.
Water spray or fog may be used to disperse the vapors. The contaminated runoff water created when using this mitigation technique must be contained by constructing containment ponds by diking earth, clay, sand, or other absorbent materials around the spilled material or, if the proper equipment is available, digging a pond to hold the ethyl acrylate. Use compatible tools and equipment–made of materials that are nonsparking and compatible with (resistant to) ethyl acrylate. In addition, all electrical equipment must be explosionproof; no flammable vapors should be exposed to electrical sparks generated by electrical motors or batteries. Block catch basins and other entries to the sewer systems. Once the liquid is contained, professional salvage personnel–not emergency responders–may suction it from the containment pond or pit and place it in secure containers.
While the salvage and cleanup operations are being carried out by professionals, the environmental authorities activated by the emergency response plan must determine how much of the soil and other materials must be removed to decontaminate the site. The amount, of course, depends on how far or deep the contaminating material has traveled. Liquid remaining in the pond or pit after the suctioning-out process has been completed may be absorbed by applying cement powder, clay, fly ash, hay, peat, sand, sawdust, soil, straw, or other sorbent materials. This absorbed material must be handled carefully; since it contains ethyl acrylate liquid, it must be disposed of in accordance with federal, state, and local regulations.
Efforts must be made to prevent ethyl acrylate from entering sewers and waterways. If ethyl acrylate enters a sewer system, explosive vapors will be generated and may spread throughout the system, threatening the entire city with an explosion. Of course, the vapors, like the liquid, will flow downgrade; but they will move upward once the system downgrade is “filled” with vapors. Alert all sewage-treatment facilities immediately; care must be exercised throughout the system.
If ethyl acrylate enters a waterway, the liquid, since it is only very slightly soluble in water and has a specific gravity of 0.923, will float on the water`s surface. Alert downstream users of the water immediately, and all use of the water must be discontinued until the environmental experts declare it safe for use. Techniques–such as containment booms, surface-skimming devices, bypass dams, and adsorbents–may be used to skim or otherwise remove oil from a waterway.
Since ethyl acrylate is only very slightly soluble in water, explosive vapors will be produced as the liquid floats on top of the water, unless the water temperature is lower than 44°F. The warmer the water, the faster the evolution of explosive vapors. If the waterway has steep banks, a considerable buildup of the vapors on the water`s surface will produce a highly dangerous explosion risk.
The contaminated water may be diverted into low-lying areas, if any, near the waterway to allow it to flow downstream, allowing for the removal of dissolved product as well as product floating on the surface. Once the contaminated water has been diverted out of the waterway bed and contained, skimming techniques may be used to remove the ethyl acrylate on the surface while activated charcoal is gently mixed into the water to adsorb the dissolved ethyl acrylate. Floating contaminants also may be removed by absorption. Hay, peat moss, straw, or other compatible materials may be used to “soak up” the ethyl acrylate on the surface. The dissolved product also can be removed by agitation and aeration.
Care must be taken when disposing of all materials used to absorb or adsorb the ethyl acrylate since the flammable material is still present. The other techniques, especially agitation and aeration, will force the dissolved ethyl acrylate out of the water, and explosive vapors may be present. Environmental authorities are responsible for monitoring the purification techniques carried out by professionals trained in those techniques; they will continuously test the water downstream to determine when it can be safely used again. The water must be safe not only for human consumption but also for industrial use. If water contaminated by ethyl acrylate is allowed to enter an industrial operation, a dangerous accumulation of vapors may occur when it contacts a hot surface or equipment.
Sealed containers of ethyl acrylate exposed to flames or the radiant heat of a fire will catastrophically fail due to the rapid pressure rise caused by absorbed heat energy from the fire. The container failure will be explosive; in essence, it could be a BLEVE. The containers must be cooled with flooding amounts of water delivered by unmanned appliances from as far away as possible. Firefighters should never let themselves be caught between a fire and containers that might explode when exposed to heat.
Pressure-relief valves on heated containers will be venting flammable vapors and almost always will be ignited, adding additional heat energy and danger to the situation. The danger of a potential BLEVE from impinging flames is bad enough, but responders must keep in mind that ethyl acrylate is a monomer as well as a flammable liquid. Exposure to heat will sensitize the monomer by overcoming the stabilizing effect of the inhibitor (as well as possibly driving the inhibitor completely out of the monomer), making a violent, explosive, runaway polymerization imminent. Regardless of which explosion occurs (and by what mechanism), the results will be disastrous.
Water, if applied in the proper manner, may be used to extinguish burning ethyl acrylate. A high-pressure water spray may be effective if applied in the same manner as for other burning flammable liquids. Foam (AFFF) may be used to blanket the burning liquid if it can be applied in the quantities appropriate for the volume of the liquid burning. Dry chemical and carbon dioxide may be used on smaller fires if the proper terrain and atmospheric conditions exist.
PROTECTIVE CLOTHING AND EQUIPMENT
Since ethyl acrylate is a suspected human carcinogen as well as an irritant and a toxin, protective clothing and equipment must prevent the liquid or vapor from contacting the eyes, skin, and respiratory system. Splashproof chemical goggles, a face shield, and positive-pressure self-contained breathing apparatus must be used. Rubber boots, gloves, aprons, and other impervious clothing will offer some protection. According to one reference, total encapsulating suits made only of butyl rubber, polyvinyl alcohol, and Teflon® offer adequate protection. Consult manufacturers of total encapsulating suits and ethyl acrylate monomer for their recommendations.
Inhalation. Move the victim to fresh air. If breathing has stopped or becomes difficult, administer artificial respiration. (Mouth-to-mouth resuscitation may expose the first-aid provider to the material in the victim`s mouth or vomit.) Provide medical attention immediately.
Ingestion. Give the victim at least two glasses of water and induce vomiting. Never force an unconscious person to drink anything or to vomit. Call for immediate medical attention while making sure the victim is warm and comfortable.
Skin. Remove all contaminated clothing, and wash all affected body areas with large amounts of water. Medical attention is necessary if irritation of the skin persists after washing.
Eye contact. Immediately flush the eyes with large amounts of water for 20 minutes, occasionally lifting the eyelids. Provide medical attention immediately. n
acrylic acid, ethyl ester
2-propenoic acid, ethyl ester
IDENTIFICATION NUMBERS AND RATINGS
(Chemical Abstract Services)
(Standard Transportation Commodity Code)
(Registry of Toxic Effects of Chemical Substances)
(United Nations/North America)
(Resource Conservation and Recovery Act)
(Chemical Hazard Response Information System)
(U.S. Department of Transportation)
flammable liquid 3
NFPA 704 Rating
(National Fire Protection Association)
(International Maritime Organization)
3.2, flammable liquid substance
FRANK L. FIRE is the vice president of marketing for Americhem Inc. in Cuyahoga Falls, Ohio. He`s an instructor of hazardous-materials chemistry at the University of Akron as well as an adjunct instructor of haz mats at the National Fire Academy. Fire is the author of The Common Sense Approach to Hazardous Materials and an accompanying study guide, Combustibility of Plastics, and Chemical Data Notebook: A User`s Manual, published by Fire Engineering Books. He is an editorial advisory board member of Fire Engineering.