
METHYL CHLORIDE
HAZARDOUS MATERIALS
CHEMICAL DATA NOTEBOOK SERIES #37
METHYL CHLORIDE is a flammable, toxic, corrosive, narcotic, clear, colorless gas with a sweet aroma similar to ether. It is easily liquifiable and therefore Is usually stored and/or shipped as a liquid under pressure. Its major uses are as a solvent, an extractant, propellant, herbicide, topical anesthetic, refrigerant, catalyst carrier in low-temperature polymerization, and is used to manufacture drugs, fumigants, herbicides, and many other chemicals.
PROPERTIES
Methyl chloride has no flash point, and, since it is a gas, it will always be ready to burn. Even as a liquid it is under pressure, and when that pressure is released, flammable gas will be generated in very large quantities. It has an ignition temperature of 1,170°F and a flammable range of 8.1 to 18.7%. The liquid has a specific gravity of 0.92, a vapor density of 1.74, and a molecular weight of 50.5. It boils at – 11.6°F, freezes at – 1439°F, and is slightly soluble in water. Its chemical formula is CH3C1, and its structural formula is
HAZARDS
Methyl chloride is usually stored and/ or shipped as a liquid under pressure. Any leak in the container will involve potentially large volumes of gas escaping under some considerable force from within (the vapor pressure of methyl chloride is 70.5 psia, which means its vapor pressure is 4.8 times that of atmospheric pressure). Any liquid that is released will evolve tremendous quantities of flammable, toxic, and corrosive gas.
Methyl chloride does not react quickly in water, but whenever it comes into contact with moisture it will hydrolyze to hydrogen chloride gas, which in turn will dissolve in moisture to become hydrochloric acid.
Its fairly wide flammable range and its vapor density of 1.74 means that any vapor generated from a release will hang near the ground and flow along low spots. Accumulation of gas in low areas and confined areas presents an explosive and toxic hazard. Whenever gases or vapors are in the flammable range and a suitable ignition source is present, an explosion will occur-even in wide-open, unconfined areas.
Methyl chloride has been lethal to laboratory animals in concentrations of 3,000 ppm (parts per million of air). This is only 0.3% in air, considerably below the lower flammable limit. Its odor has been reported to be detectable as low as 10 ppm. Its TLV-TWA (threshold limit value-time weighted average) is 50 ppm, and its STEL (short term exposure limit) is 100 ppm.
Inhalation of methyl chloride gas may cause narcosis and brain swelling. Symptoms of exposure include diarrhea, dizziness, abdominal pain, anemia, nausea with vomiting, weakness, confusion, and slurred speech. Continued exposure can cause convulsions, paralysis, coma, and death. Chronic exposure can cause liver and kidney damage. Some of the symptoms can be delayed for several hours. Since methyl chloride is only slightly narcotic, its symptoms may not be apparent to the victim.
Contact with the liquid or gas as it has just evolved from the liquid can cause frostbite. Eye contact with the gas can cause temporary burning of the eyes.
Ingestion of the liquid will cause frostbite of the mouth, tongue, and esophagus. It will also produce symptoms similar to those of inhalation.
Methyl chloride reacts corrosively with aluminum, magnesium, zinc, and their alloys, especially if the metals are powdered. When in the presence of moisture, hydrochloric acid may be formed, which will react with these metals to liberate flammable (explosive) hydrogen gas. Methyl chloride will also react with some rubber and plastic compounds and is incompatible with lithium, sodium, and potassium. Even so, methyl chloride is considered a stable chemical.
METHYL CHLORIDE
SYNONYMS
Artie monochloromethane
chloromethane R 40
Freon 40
IDENTIFICATION NUMBERS AND RATINGS
CAS
(Chemical Abstract Services)
74-87-3
STCC
(Standard Transportation Commodity Code)
4905761
RTECS
(Registry of Toxic Effects of Chemical Substances) PA6300000
UN/NA
(United Nations/North America)
1063
CHRIS
(Chemical Hazard Response Information System)
MIC
RCRA
(Resource Conservation and Recovery Act)
U045
DOT
(U.S. Department of Transportation)
Flammable gas
NFPA
2-4-0
IMO
(International Maritime Organization)
2.3, poison gas
In addition to the hydrolysis which produces hydrogen chloride, methyl chloride’s combustion products include hydrogen chloride, carbon monoxide, carbon dioxide, and water.
NONFIRE RELEASE
As in any incident involving flammable gases, flammable liquids, or toxic materials (or any hazardous material, for that matter), approach must always be made from upwind, and all ignition sources must be eliminated. All unnecessary personnel must be kept from the danger area or secured area, and the proper environmental authorities must be notified. It is always recommended that Chemtrec be called (800-4249300) in addition to the manufacturer of the product and the company to which the material is being shipped. No matter what the nature of the release, notification of the danger and evacuation of the population within 3,000 feet of the container and further downwind is always in order.
If the container is leaking gas or a small liquid stream that is immediately evaporating, evacuation downwind should be carried out. If the container can be plugged or otherwise sealed safely by emergency responders, that may be considered. The emergency responders must be properly protected from the toxic, corrosive, and narcotic effects of the gas, and all efforts must be made to eliminate ignition sources. Methyl chloride’s vapor density is greater than 1.0, which means the gas will flow downhill, seeking an ignition source. Once that source is reached, the gas will ignite (perhaps explosively), and flash back to the source. If the leak cannot be stopped safely, other mitigation techniques must be considered. In any event, materials and/or tools used to stop the leak must be compatible and nonsparking.
The gas may be dispersed by a water fog or spray, but care must be taken to prevent the runoff from spreading. Also, remember that the hydrolysis of methyl chloride will produce hydrochloric acid. If movement of the contaminated water can be contained, this technique may be preferable to trying to stop the leak.
If the leak is large, consider the building of containment ponds by making dikes of soil, sand, clay, or other materials. A containment pit may be dug, with trenches leading from the leak to the pit. The pit may be preferable (if easy to dig) since the surface area of the liquid will be smaller in the pit, and the less liquid exposed to the atmosphere means that less gas will be generated from the boiling liquid.
Foam may be applied to the surface in an attempt to reduce the production of vapors, but again, since all foams are water-based, the hydrolysis of the methyl chloride will generate hydrogen chloride vapors. Since methyl chloride is a gas and its vapor pressure is high, this technique may not be effective. It may percolate into the soil, and its dispersion may be delayed.
All efforts must be taken to prevent methyl chloride from entering into sewer systems. The liquid will produce large quantities of flammable and toxic gas, which will rapidly expand throughout the sewers, presenting an explosive and toxic potential throughout the system. If the material does enter a sewer, evacuation of any place where the vapors may spread must be considered, and the sewage treatment facility must be warned.
If the product does enter a waterway, alert all downstream users. Movement of the contaminated water may be interrupted by the use of containment dams or by diverting the water into a lowlying area next to the waterway. Dammed water or impounded water can then be removed or treated in place to remove the contamination. Absorbents such as activated charcoal may be added to the water to remove contamination.
However, since methyl chloride is a gas, much of it can be removed from the water by agitation or aeration by sparging or air stripping. Ordinarily, when a liquified gas contacts water, it will boil away rather quickly, but some of the methyl chloride will dissolve in the water. It is this contamination that must be removed.
In all cases, the product is flammable and toxic. Emergency responders must protect themselves from the vapors and use compatible tools. Environmental authorities should be consulted on all mitigation alternatives, and it is they who will decide whether the contamination has spread or not.
FIRE SITUATION
Whenever a container holding a liquified gas is exposed to the radiated heat of a fire or the heat of impinging flames (with the possible exception of cryogenic containers, which are insulated), a violent release of the material is to be expected as the container fails catastrophically.
As the liquid is heated within the container, the pressure-relief valve (usually a spring-loaded valve) will be forced open by the rising pressure and some gas will be vented. If an ignition source is nearby, the gas will ignite, producing a tongue of flame from the vent. This flame should not be extinguished unless the flow of gas can be stopped immediately after extinguishment. If there is no nearby ignition source, the gas will flow upward at first, due to the relatively high temperature of the gas. As it cools, it will sink because of its vapor density and begin to flow along the ground. Eventually, it will find an ignition source (Murphy’s Law, which says that if anything can go wrong, it will), explode, and flash back to the source, trapping firefighters near the container (O’Brien’s Law, which says Murphy was an optimist).
If the container is being impinged by flame, a BLEVE (boiling liquid, expanding vapor explosion) may be imminent. If the flame is impinging above the liquid level, the tank will continue to heat and the metal may be weakened, both by the high heat of the flame and the rising pressure within the tank. As the metal continues to weaken, it may part slightly, exposing liquified gas (at a temperature considerably above its boiling point) to normal atmospheric pressure. The resulting rapid expansion as liquid turns to vapor will widen the tear in the metal, and the release of pressure may propel the container (or parts of it) some distance. As the vapor leaves the tank, it will be ignited by the impinging flame, producing a fireball of awesome proportions, perhaps up to 1,000 feet wide. Anyone within 500 feet of the tank will he caught within the fireball. The danger zone (radiated heat and pressure rise) will be at least another 2,000 feet.
METHYL CHLORIDE
The BLEVE is one of the most horrible and deadly events a firefighter can face, and for this reason, heated tanks must be cooled from great distances, using unmanned appliances. If there is no life exposed and the incident is far from any other exposure, it may be safer to let the fire burn itself out or let the BLEVE occur with no one around.
If the flame is accidently extinguished, there will be rapid build up of explosive vapors. If the safety relief valve is venting straight up or at a steep angle, it may be safe to try to deliberately reignite the vented gases. However, this alternative should be considered extremely dangerous and should be carried out only if the chance of an explosion is considered nonexistent.
Just because an impinging flame is below the liquid level on the tank, it must not be assumed that a BLEVE will not occur. The heat may be so intense and the liquid producing so much vapor that either the liquid level could drop below the original point of flame impingement, thus removing the heat sink property of the liquid behind it, or the ‘ rise in pressure could be more than the vent could relieve. In either situation, the BLEVE could occur.
GLOSSARY
Aeration-The process by which air is passed through a liquid.
Air-stripping-A process by which a material is pumped through an air chamber or sprayer into the open air at high pressure to remove contaminants.
Extractant-A solvent that is used to separate a material from a mixture or solution.
Halogenated hydrocarbon-A hydrocarbon compound that has had one or more hydrogen atoms replaced by a halogen (fluorine, chlorine, bromine or iodine)
Hydrolyze-When a substance reacts with water to form two or more new substances. The reaction is called hydrolysis.
Sparging-A process by which air or another gas is bubbled through a liquid, solid, or another gas to remove a contaminant.
STEL-The maximum amount of material to which a person may be exposed over a short time period (usually 15 minutes) without harm.
TLV-TWA-The amount of material to which a person may be exposed for 8-hours-a-day, 40-hours-a-week with no harmful effects. The amounts are a weighted average over the time period.
Water, dry chemical, and carbon dioxide are recommended fire extinguishing agents, depending on the size of the spill and wind and weather conditions. Water should be used to cool the containers, again, from a safe distance. Any water used on a spill will increase the evolution of vapors. The old rule was to approach a tank from the sides and not the ends, but the first BLEVE caused the adoption of a new rule: Do Not Approach the Tank!
Methyl chloride is a halogenated hydrocarbon, which means its products of combustion include (in addition to carbon, carbon monoxide, carbon dioxide, and water) hydrogen chloride. One reference includes phosgene as a combustion product, and phosgene is extremely toxic. Hydrogen chloride is an irritant acid gas, which, when dissolved in water, forms hydrochloric acid.
FIRST AID
For inhalation, the victim must be removed to fresh air immediately and kept warm and quiet. Artificial respiration should be administered if breathing becomes difficult or stops. Mouth-tomouth resuscitation will expose the provider of first aid to the product in the victim’s lungs and/or vomit. Immediate medical attention must be sought.
For eye contact, the eyes must be flushed with water for a minimum of fifteen minutes, with occasional lifting of the eyelids. Immediate medical attention is necessary.
For skin contact, care must be taken if frostbite has occurred. Affected areas of skin should be washed with soap and water, being careful not to use hot water. Medical attention is necessary.
Ingestion is unlikely, but if it has occurred, the victim must be made to drink warm water. Never try to make an unconscious victim drink anything. If a victim has ingested methyl chloride, he will need immediate medical attention.
PROTECTIVE CLOTHING AND EQUIPMENT
Personnel must protect themselves from breathing methyl chloride vapors by using positive-pressure SCBA with full facepiece.
Clothing should prevent the liquid from contacting the skin, and the eyes must be protected with face shields and splash-proof safety goggles. Rubber boots, gloves, and aprons may be worn to keep the liquid from the skin, but the most conservative approach requires the use of a total encapsulating suit. Manufacturers of such suits claim that neoprene, nitrile-butadiene rubber (NBR), and Viton will offer protection. The selection of a total encapsulating suit must be made after consulting the manufacturer for the most resistant material that can be used, in addition to several other factors. The thickness of the material should be considered, plus integrity of the seams, the chemical to which it will be exposed, the concentration of that chemical, and the length of time of exposure. There is no one material that will resist all chemicals, so a great deal of thought must go into the selection process, which incidently, might call for the purchase of at least two types of suits