CHEMICAL DATA NOTEBOOK SERIES #97: METHYL METHACRYLATE
HAZARDOUS MATERIALS
Methyl methacrylate is a flammable, irritating, colorless liquid with a fragrant, fruity, but sharp odor. Its main use is as a monomer (a “tiny” molecule possessing the unusual chemical property of being able to react with itself to form a polymer) for one of the most popular acrylic plastics.
Methyl methacrylate has a flash point of 50°F, an ignition temperature (sometimes referred to as the autoignition temperature) of 790°F, and an explosive range of from 2.1 to 12.5 percent in air. It has a specific gravity of 0.95, a molecular weight of 100, and a vapor density of 3.45. It freezes at -54°F. boils at 214°F, and is slightly soluble in water. Its molecular formula is CH,C(CH,)COOCH..
HAZARDS
Methyl methacrylate’s major hazard is that it is a flammable liquid. Its flash point of 50°F means that at most temperatures in industrial situations, the liquid will generate vapors sufficient to form an ignitable mixture with the air near the liquid’s surface. Its ignition temperature of 790°F is reachable by all common ignition sources, and its explosive range is wide enough that once the lower explosive limit (LEL) is reached. it will be very difficult to get concentrations above the upper explosive limit (UEL). Methyl methacrylate vapors are 3.45 times as heavy as air, as indicated by a rather high vapor density of 3.45. The implication of a very high vapor density is that the vapors will “hug” the ground, flow along low spots in the terrain, and accumulate in low spots and confined areas. Flowing vapors of flammable and combustible liquids always seem to move toward likely ignition sources. Once the vapors reach such an ignition source, the vapor/air mixture will explode and flash back to the original source of the vapors.
Methyl methacrylate vapors irritate the skin, eyes. nose, throat, and respiratory system. Inhaling high concentrations can produce drowsiness, headache, nausea, vomiting, and possibly narcosis. Death can occur under some circumstances. Methyl methacrylate has a TLV-TWA (threshold limit value-time weighted average) of 100 ppm (parts per million of air) and a STEL (short-term exposure limit) of 125 ppm. An additional hazard is present in low-lying areas or confined spaces, where methyl methacrylate may accumulate. Anyone entering such a space without respiratory protection could suffer anything from severe lung irritation to unconsciousness and death.
Methyl methacrylate’s almost exclusive use is as a monomer that when polymerized forms polymethyl methacrylate (PMMA), the most popular of the wide family of acrylic plastics, which includes—in addition to polymethyl methacrylate—ethylene acrylic acid (EAA) copolymers, ethylene butyl acrylate, ethylene-ethyl acrylate (EEA), ethylene methacrylate, and ethylene methacrylic acid copolymer. All monomers of thermoplastics are hazardous materials of one sort or another. Since methyl methacrylate is a monomer, it is an inherently unstable chemical. It will react with strong acids, strong alkalis, strong reducing agents, and oxidizers (including organic peroxides and any other material that is an initiator for polymerization).
Polymerization is the process through which a monomer reacts with itself to form a giant molecule, called a polymer, under controlled conditions in a polymerization container (reactor), in which the heat and pressure applied to the monomer are carefully controlled. Polymerization is an exothermic reaction, and the evolved heat must be systematically removed. If this reaction were to occur outside the reactor, the released heat would build up so rapidly that the polymerization reaction would be out of control (uncontrolled or runaway polymerization). Sometimes, this uncontrolled chemical reaction produces an explosion that resembles a BLEVE (boiling-liquid, expanding-vapor explosion). This uncontrolled reaction can occur any time the monomer’s temperature is significantly raised. To prevent the polymerization reaction from beginning prematurely, a chemical called an inhibitor or a stabilizer is added to the monomer. As long as this inhibitor stays dissolved in the monomer, the monomer will be somewhat impervious to a rise in temperature. However, if the temperature increases enough and pressure over the liquid is released, the inhibitor will be forced out of the monomer. Now unprotected, the monomer will begin to polymerize, producing heat as the reaction proceeds. As this evolved heat is absorbed by the unreacted monomer, the reaction proceeds faster, producing even more heat. Inhibitors for methyl methacrylate include hydroquinone. hydroquinonc methyl ether, and dimethyl tert-butylphenol.
A rule of thumb in chemistry states that as the temperature of reacting materials increases by 10°C (18°F), the speed of the reaction will double. As the materials continue to react and the temperature of the reactants continues to rise, the reaction speeds up and the release of heat speeds up. Very rapidly, the reaction increases its speed until it literally explodes. For this reason, the polymerization reactor must be able to withstand certain pressures and to remove the evolved heat as it is produced. For this reason also, emergency responders must be aware of the explosive hazards of monomers in general as well as of the temperatures and pressures to which the material has been exposed and for how long a period of time. The emergency responder must realize that the container (sometimes as large as a rail tank car) may explode with deadly results.
NONFIRE RELEASE
A release of any appreciable quantity of methyl methacrylate should activate the community’s emergency response plan. Since fire and explosion are imminent once the material is released, the local fire department will almost always assume command of the incident. The exception to this rule is when federal, state, or local law names some other emergency response organization to command the incident. The fire chief or head of the local fire department’s hazardous-materials response team usually will serve as incident commander.
Treat a release of methyl methacrylate 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 and nonemergency responders from the danger zone as soon as possible; and immediately consider evacuating from an area surrounding the danger zone. The evacuation radius depends on the size of container, the amount of material present, the local terrain, and present and forecast weather conditions.
In trying to mitigate the incident, the emergency responders must consider all the chemical and physical properties of methyl methacrylate. Knowing these properties helps the responder to predict with some certainty w hat w ill occur under different sets of circumstances and within different scenarios. Knowing these hazards may save many lives, including those of the emergency responders.
Care must be taken with any methyl methacrylate liquid that may have been released from its original container. Contact with any foreign material will contaminate it. and it will be sensitized and ready to polymerize. Although it would be less dangerous if this reaction were to occur in the open than if the liquid were confined, enough heat still would be generated to volatilize the liquid, increasing the amount of vapors present in the air that could ignite and explode. The source of ignition could be the heat energy released from the reaction itself as the reaction speed increases.
SYNONYMS
acrylic acid, 2-methyl-, methyl ester
acrylic resin monomer
alpha-methyl acrylic acid
Diakon
methacrylic acid, methyl ester
methyl-alpha-methacrylate
methyl methacrylate monomer
methyl methylacrylate
methyl-2-methyl-2 propenoate
2-methylpropenoic acid
2-methyl-2-propenoic acid, methyl ester
MMA
MME
“Monocite” methacrylate monomer NCI-C50680
2-propenoic acid, 2-methyl-, methyl ester
IDENTIFICATION NUMBERS AND RATING
CAS (Chemical Abstracts Service) 80-62-6
STCC (Standard Transportation Commodity Code) 4907250 for inhibited form; 4907255 for uninhibited form
RTECS (Registry of Toxic Effects of Chemical Substances) OZ5075000
UN/NA (United Nations/North America) UN 1247 for inhibited form; NA 1247 for uninhibited form
CHRIS (Chemical Hazard Response Information System) MMA
RCRA (Resource Conservation and Recovery Act) U162
DOT (U.S. Department of Transportation) Class 3, flammable liquid
NFPA 704 Rating (National Fire Protection Association) 2-3-2
IMO (International Maritime Organization) 3.2, flammable liquid
Water spray or fog may be used to disperse the methyl methacrylate vapors. The contaminated runoff water created when using this mitigation technique must be carefully contained. Emergency containment ponds may be constructed by diking earth, clay, sand, or other absorbent material around the spilled material; or, if the proper equipment is available, a containment pond may be dug to hold the methyl methacrylate. In any event, compatible tools and equipment must be used—that is, the materials used to make the tools and equipment must be nonsparking and cannot be attacked by the methyl methacrylate. Also, all electrical equipment must be explosionproof—no flammable vapors may be exposed to any electrical sparks generated by the electrical motors or batteries. Catch basins and other entries to the sewer systems must also be blocked. 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.
All emergency responders must realize their mission, their liabilities, and their capabilities. Firefighters trained in mitigating hazardous-materials operations also must recognize their responsibilities, which, in most cases, are directed toward life rescue and containment of the released hazardous material. Most emergency responders are not properly educated, trained, or equipped to salvage or clean up at hazardous-materials incident sites.
While the salvage and cleanup operations are being carried out by professionals, the environmental authorities must determine how much of the soil must be removed. This would depend, of course, on how far or how deep the contaminating material has traveled. Any liquid remaining in the pond or pit after completion of the suctioning-out process may be absorbed by applying cement powder, clay, fly ash, hay, peat, sand, sawdust, soil, straw, or another sorbent material. This absorbed material must be handled carefully, since it contains methyl methacrylate liquid, and must be disposed of in accordance with federal, state, and local regulations.
Prevent methyl methacrylate from entering sewers or waterways. If it does enter 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 also move upward once the system downgrade is “filled” with vapors. Alert all sewage treatment facilities immediately.
If methyl methacrylate enters a waterway, the liquid, since it is only very slightly soluble in water and has a specific gravity of 0.95, will float on the water’s surface. All downstream users of the water must be alerted immediately, and all water use must be discontinued until the environmental experts declare it safe. Techniques used to skim or otherwise remove oil from a waterway, such as containment booms, surface-skimming devices, bypass dams (constructed with pipes or conduits placed well below the water’s surface to allow the subsurface water to pass through while keeping material on the surface from flowing downstream), and adsorbents, may be used to remove methyl methacrylate from the water.
Since methyl methacrylate is only slightly soluble in water, explosive vapors will be produced as the liquid floats on top of the water. If the waterway has steep banks, there could be a considerable buildup of vapors on the water’s surface, producing a highly dangerous explosion risk near that waterway.
If there are any low-lying areas next to the waterway, you can divert the water into them instead of allowing it to How downstream. This technique will allow dissolved product and product floating on the surface to be removed. Once the contaminated water has been diverted out of the waterway bed and contained, skimming techniques may be used to remove methyl methacrylate on the surface, while activated charcoal may be gently mixed into the water to adsorb the dissolved methyl methacrylate. Adsorption techniques also may be used to remove the floating contaminant. Hay, peat moss, straw, or any other compatible material may be used to “soak up” the methyl methacrylate on the surface. Agitation and aeration techniques also may be used to remove the dissolved product.
All material used to absorb or adsorb the methyl methacrylate must be carefully disposed of, since the flammable material is still present. The other techniques, especially agitation and aeration, will force the dissolved methyl methacrylate out of the water; explosive vapors may be present. The environmental authorities on the scene are responsible for monitoring purification techniques, which should be carried out by professional personnel trained in those techniques. These same environmental experts will continuously test the water downstream to determine when it is safe for human consumption and for use by industry. If water contaminated by methyl methacrylate enters an industrial operation and contacts hot surfaces or equipment, a dangerous accumulation of the vapors might occur.
FIRE SCENARIO
Sealed containers of methyl methacrylate exposed to flames or the radiated heat of a fire will be subject to a catastrophic failure due to the rapid pressure rise caused by the heat energy absorbed from the fire. The failure will be explosive; it could be a BLEVE. Flooding amounts of water must be used to cool such containers, and the water must be delivered by unmanned appliances from as far away as possible. Firefighters must never let themselves be caught between a fire and containers that might explode when exposed to heat.
Pressure-relief valves present on the heated containers will be venting flammable vapors, and they 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 remember that methyl methacrylate 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), and a violent, explosive, runaway polymerization may be imminent. Regardless of which kind of explosion occurs (and by which mechanism), the results will be disastrous.
Water may be used to extinguish burning methyl methacrylate if applied in the proper manner. High-pressure water spray may be effective if it is applied in the same manner as it is when used against any other burning flammable liquid. Foam 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
Select protective clothing and equipment that prevent contact of methyl methacrylate liquid or vapor with the eyes, skin, or respiratory system. Use splashproof chemical goggles and a face shield for eye protection and positive-pressure, self-contained breathing apparatus. Rubber boots, gloves, aprons, and other impervious clothing will offer some protection. If total encapsulating suits are worn, one reference states that only polyvinyl alcohol, Teflon®, and polyethylene/ethylene vinyl alcohol will offer adequate protection. Consult the manufacturers of the total encapsulating suits and the methyl methacrylate monomer for their recommendations.
FIRST AID
Inhalation. Move the victim to fresh air. If breathing has stopped or becomes difficult, administer artificial respiration (mouth-to-mouth resuscitation may expose the provider of first aid to the material in the victim’s mouth or vomit). Medical attention must be provided immediately.
Ingestion. Give the victim large amounts of water to drink 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 contact. Remove all contaminated clothing and wash all affected body areas with large amounts of water. Medical attention is necessary if skin irritation persists after washing.
Eye contact. Immediately flush the eyes with large amounts of water for 20 minutes, occasionally lifting the eyelids. Provide immediate medical attention.
