Methyl Ethyl Ketone

Methyl Ethyl Ketone


Chemical Data Notebook Series #25:

Methyl ethyl ketone, better known as MEK, is among the most widely produced chemicals in the United States. Its odor is familiar to anyone who has been around cleaning fluids, some paint strippers, and nail polish remover. Its dangers are very common. MEK is moderately toxic and flammable, and it poses many potential dangers for responders in event of a spill or fire.

MEK is a solvent for plastic resins, coatings, and films. Because it is so powerful, it is used in the manufacture of adhesives and cements, in making wax from petroleum, as a printing catalyst and carrier, and in the manufacture of smokeless powder.

MEK is irritating, volatile, and somewhat pungent. Its flash point is 16°F, attesting to its flammability. The solvent’s ignition temperature is 759°F, and its flammable range is from 1.4% to 11.5% in air. It has a specific gravity of 0.806, a molecular weight of 72, and a vapor density of 2.49. It boils at 175.3°F, freezes at -123.3°F, and is moderately soluble in water. It is stable in that it does not react with water. But it reacts with strong oxidizing agents. It is not corrosive to metal, but softens some plastics.

The molecular formula for MEK may be written as either (CH3)2CH2CO or, more commonly, CH3COCH2CH3. It can also be written C4H8O, which can be very misleading. The student of hazardous-materials chemistry recognizes the “CO” group, or radical, in the structural formula, and knows it is a ketone. He or she also recognizes the fact it is a flammable liquid from the “short chain” hydrocarbon radical attached to this carbonyl group.

MEK, if ingested, causes irritation of the mouth, throat, and stomach. There is no specific lethal dose information available for humans, but toxicity for rats has been measured, producing an LD50 (see glossary, page 106) of 0.5 grams per kilogram.

Inhalation of high concentrations of MEK vapors has a narcotic effect and depresses the central nervous system. Symptoms include dizziness, drowsiness, headache, nausea, weakness, vomiting, and loss of consciousness. Continued inhalation of vapors could cause death. The first symptoms are noticeable near 300 parts per million (ppm), which is the short term exposure limit (STEL) for methyl ethyl ketone. The threshold limit value – time weighted average (TLV-TWA) for MEK is 200 ppm. There is no immediately dangerous to life and health (IDLH) value listed. Its odor may be detected at levels between 10 and 15 ppm.

Contact of MEK vapors with the eyes, nose, and throat produces irritation in these organs. Contact of the liquid with the eyes causes irritation and possible permanent damage. Contact of the liquid with skin causes irritation by defatting.

Precautions on approaching a MEK spill are the same as for any flammable liquid: approach from upwind, eliminate all ignition sources, isolate the area, and evacuate downwind. The spilled product must be prevented from entering sewers and waterways. This can be done by constructing a containment pond by diking the area around the spill with dirt, sand, clay, or other absorbent materials. Trenches or ditches may be dug to contain the product or can be used to direct the liquid to a containment pit that is dug.

Containment ponds are usually easier to construct, but are generally shallower and larger in surface area than a pit or trench. The larger the surface area, the more rapid the generation of explosive vapors. Also, the smaller the surface area, the easier it is to cover the liquid with a tarp or with the application of alcohol-type foam. Both procedures are appropriate to slow down the evolution of vapors. If the foam breaks down, reapplication may be necessary. With each application of foam, contamination of the product will occur, making its salvage value less and less.

Once the liquid is contained, it may be salvaged by suction or vacuum pumping into secure containers. This should be done only by experienced professionals using the proper equipment: explosionproof motors and switches which prevent the salvage equipment from becoming an ignition source. Salvage should not be a normal duty for firefighters or other first responders to a hazardous materials incident unless they are properly educated, trained, and equipped. Even in that case, salvage should be reserved for professionals unless the emergency dictates immediate removal of the product.

If the spill is caused by a leaking container, and the leaking product may be caught in another type of container, it may be collected to be pumped back into the leaking container. Be cautious when using portable tanks utilizing sheets of plastic as the containing element, since MEK might dissolve, soften, or weaken it. In any case, the material may be ruined. (This is also true if you attempt to cover a spill with plastic sheeting, although it is not as critical as trying to contain the liquid, since failure of the sheeting will not cause spreading of the liquid.) The act of pumping the liquid back into the leaking container gives a sort of semiclosed system, which may or may not be desirable. On one hand, it prevents contamination of the soil and the product; on the other hand, the procedure could cause a dangerous generation of vapors.

If the leak can be plugged by driving wooden plugs (rubber or plastic may dissolve) using a nonsparking hammer, or if any other emergency patching system can be implemented, it should be done as soon as possible.

Should the liquid enter a sewer or waterway, the sewage treatment plant and all users of water downstream must be notified immediately. It is assumed that the proper environmental authorities have also been called. The MEK will float on the surface of the water for a short while until it all dissolves. There will probably be no time to use floating booms to contain the MEK before it dissolves.

If the waterway can be diverted to contain the dissolved MEK, it should be done immediately, preventing the product from moving downstream. Once it has escaped and is flowing downstream in solution, the problem is magnified.

The product may be removed from water with the use of activated charcoal, which works by adsorption rather than absorption. Any remaining product may be removed by aeration, stripping, or sparging. Again, this work should be done by professionals using the proper equipment. Activated charcoal recovered from the process will have a flammable liquid on its surface. Air stripping, sparging, and aeration all generate vapors from the contaminated water, so the hazard remains present.

Where MEK vapors are being generated by a spill, water fog or spray may be used to reduce the amount of vapors by dissolving them out of the air. Care must be taken to control the runoff. A sweeping motion by one or more spray nozzles applied just above the surface of the liquid and immediately downwind of the spill should effectively reduce and disperse the vapors leaving the scene of the spill. Flammable vapor detectors specific for MEK should be used downwind to determine if vapors have escaped. Evacuation downwind should always be considered. Attention should be given to low spots and confined areas.

As the solubility of MEK in water is used in the “sweeping” of the air with fog or spray, so should dilution be considered as a mitigation technique. The addition of water to the spill effectively raises the flash point to safe levels. Of course, dilution should be used only when the resulting volume of MEK-water solution can be contained until it is removed.

Removal of spilled product, dissolved or contaminated product, and contaminated soil and diking material should be done by professionals, under guidance of the proper environmental authorities. These authorities should decide how much contamination of the soil has occurred, and should instruct the professionals on how much to remove. They will also decide where contamination may have spread downstream, and when it is safe to use the water once again.

Where removal has been delayed, or dilution and/or salvage are not possible, the MEK may be absorbed by the use of soil, sand, clay, cement powder, fly ash, saw dust, straw, peat moss, or any other compatible material. Any equipment used to remove soil or absorbent must not produce an ignition source, otherwise a fire or explosion might occur. Any spilled MEK exposed to air generates considerable amounts of vapor. Its vapor density of 2.49 indicates that the vapors “hang together” and flow along low spots in the ground, seeking an ignition source. If one is found, the vapors explode, and flash back to their source. They also collect in confined areas, potentially producing an extremely hazardous explosion and fire situation for exposed personnel.

With a flash point of 16°F, any spilled MEK is produces vapors sufficient to form an ignitable mixture with the air near the surface of the liquid (the definition of flash point) at all temperatures of the liquid from 16°F and higher.





Ethyl methyl ketone


Methyl acetone

Identification Numbers and Ratings


(United Nations/North America)


National Fire Protection Association 704 rating



(Chemical Abstract Service)



(Registry of Toxic Effects of Chemical Substances) National Institute of Occupational Safety and Health



(Standard Transportation Commodity Code)

Association of American Railroads, Bureau of Explosives



(Chemical Hazard Response Information System)

U.S. Coast Guard



(International Maritime Organization)

3.2, flammable liquid

NOTE: Both the IMO and the U.S. Department of Transportation accept ethyl methyl ketone as a proper shipping name for the material.

The term “flash point” comes from the reaction that occurs in the laboratory as a technician warms up a liquid whose vapors are exposed to an ignition source, and denotes the temperature at which a flame “flashes” across the surface of the small cup used in the testing apparatus. It is extremely important to note that this small “flash” in the laboratory becomes an explosion in a real-world spill, with the size and devastation of the explosion directly linked to the volume of the spill, its surface area, the ambient temperature, and wind conditions. The longer a large surface area of the liquid is exposed to high temperatures, the larger the buildup of vapors, and the more powerful the explosion.

There will always be some argument as to whether or not the temperature of the liquid must reach its fire point (the temperature of the liquid at which it produces vapors sufficient to produce sustained combustion), but this is a moot point. The fire point is only about 3°F to 8°F higher than the flash point, and the fire point is reached very easily by the liquid being treated by radiated heat from the “flash.” There can be no argument that the most important property of any liquid producing vapors that burn is its flash point.

Where a container of MEK is being threatened by impinging flame or radiated heat, a danger of container failure exists. All containers exposed to heat or flame must be cooled by the application of water from as far away as possible, or by unmanned appliances. If the containers cannot be cooled, withdrawal and evacuation are warranted in a radius of from 500 to 2,000 feet, depending on the size of the container. If the container fails, it will do so explosively, spewing flaming liquid in all directions.

The final combustion products of MEK will be water, carbon, carbon dioxide, and carbon monoxide. Anyone fighting the fire should be wearing respiratory protection. The fire may be fought by using carbon dioxide or dry chemical on small or confined fires. Alcohol-type foam is effective, but might have to be applied several times during the incident. Water applied as a spray or fog is also effective in cooling down the fire and extinguishing it. Remember that foam and water, when used to fight the fire, will add volume to the pool if confined. The amount of additional volume that the confinement techniques can hold must be considered in the mitigation decision.

If the ambient temperature and the temperature of the liquid are below 16°F, fire will not occur unless localized heating of the liquid occurs and an ignition source sufficient to heat the vapors to 759°F is present. In cold weather below 16°F, the only actions needed might be evacuation and monitoring the air until the spilled product can be removed.

Any equipment used or clothing worn should prevent contact with the eyes, skin, and respiratory system. This may include face shields, splash-proof goggles, rubber boots, rubber gloves, or other clothing that the manufacturer claims is impervious to MEK, which may include butyl rubber.

For respiratory protection, a positive-pressure self-contained breathing apparatus should be used. Some references suggest the use of a gas mask, equipped with an organic vapor cartridge respirator with full face pieces, within the safety-use limitations of those devices. However, it is risky to use such a device unless the concentration of MEK vapor is known —the vapor concentration may exceed specifications of the device. It is always best to use an SCBA.

Should a victim inhale MEK, he or she should be removed to fresh air. If the victim has stopped breathing, or breathing has become difficult, artificial respiration must be administered (mouth-tomouth resuscitation may expose the provider of first aid to the material in the victim’s mouth or vomit). Medical attention must be provided immediately.

In case of ingestion, the victim, if conscious, should be induced to drink a strong solution of salt water. One should never try to make an unconscious person drink anything or vomit.

For contact with the skin, all contaminated clothing should be removed and all affected body areas washed with large amounts of water. Medical attention is necessary if irritation of the skin persists after washing.

If there is eye contact with MEK, the eyes should be flushed immediately with large amounts of water for 15 minutes, occasionally lifting the eyelids. Medical attention should be provided immediately.


Absorption—The penetration of one substance into the inner structure of another substance.

Adsorption—The adherence of one substance to the outer surface of another substance.

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.

Combustible liquid— A liquid with a flash point higher than 100°F.

Explosion-proof— Usually refers to switches, lights, motors, and other devices run by electricity that have all areas which might produce an electrical discharge, or spark, covered so that no flammable gas, vapor, fume, or dust can be ignited by such discharge.

Flammable liquid—A liquid with a flash point less than 100°F.

LD50—A measured amount of material is fed to a group of test animals, which are then observed for a standard observation period, usually 14 days. The amount fed to the animals that results in the death of half the test animals during the observation period becomes the LD50.

Sparging—A process by which air or other gas is bubbled through a liquid, solid, or gas to remove a contaminant.

Volatile—The capability of evaporating rapidly at normal temperatures and pressures.

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