CHEMICAL DATA NOTEBOOK SERIES #34 Methyl Bromide
HAZARDOUS METERIALS
MHTHYL BROMIDE is a toxic, corrosive, irritating, colorless gas with a sweet odor and burning taste. It is usually shipped and stored as a liquid under pressure. It is used as a degreaser, disinfectant, fumigant, herbicide, pesticide, refrigerant, solvent, and as a raw material for making other chemicals.
Although methyl bromide is considered practically nonflammable, it will burn. As a gas, it has no flash point, but it has a flammable range of 10% to 16%. Some references show the flammable range from 13.5% to 14.5%, which would make ignition difficult since it would have such a narrow flammable range (of 1%). However, within whatever its flammable range is, it will ignite at 999°F.
A word of caution is due here. There are several methods of determining flammability properties of materials. The fact that different values show up in different references for the same product indicates only that different methods may have been used to determine those values. An emergency responder needs to know what hazard he or she faces when responding to any incident, and the information contained in one reference book may not provide all the information needed. When emergency responders find different information in different references, they must choose the most conservative of the numbers in order to protect themselves. This writer, when researching information for this series of articles, always uses the information that will indicate the lowest flash point, the lowest ignition temperature, the widest flammable range, the lowest boiling point, et cetera from all the reference sources examined. This is done to provide the reader with the most conservative set of properties possible, so that the user of such information will have the best chance of handling the incident without injury or death to himself or herself.
The flammable range of methyl bromide might indeed be 13 5% to 14.5%, but would you bet your life or the life of those in your command on it? As long as there is evidence that the range might be wider, it is absolutely necessary for the number one exposure, the emergency responder, to investigate the differences, and, taking the conservative approach, accept the wider flammability range (or more conservative property of another nature) until it is disproven.
In its liquid form, methyl bromide has a specific gravity of 1.68; as a gas, it has a vapor density of 3.27. Its molecular weight is 94.94; it has a boiling point of 38.3°F., a freezing point of 135°F, and is very slighdy soluble in water.
Its molecular formula is CHjBr, and its structural formula is
Methyl bromide is toxic by all routes of entry into the body. Since it is a gas shipped and stored as a liquid, any release of the gas from the container will be under pressure, and any liquid released will generate large amounts of gas. It has a TLV-TWA (threshold limit value-time weighted average) of 5 ppm and STEL (short term exposure limit) of 15 ppm.
Inhalation of methyl bromide in low concentrations may cause blurred vision, slurred speech, headaches, nausea, and vomiting. Continued exposure will produce tremors and then convulsions. High concentrations may produce irritation of the lungs which may cause pulmonary edema. Permanent damage may be done to the central nervous system and the kidneys. Prolonged exposure may cause unconsciousness and death. One of the major problems with methyl bromide is that some of the symptoms may not manifest themselves for from short periods of time to days.
METHYL BROMIDE
Contact with the skin may cause blistering burns, but the vapors may be absorbed through the skin, causing many of the previously listed symptoms. Less severe contact can produce skin rashes.
Contact with the eyes may produce severe irritation. Eye injury may be reversible, even though temporary blindness may occur.
Ingestion of methyl bromide will cause damage to the mouth and esophagus because of its corrosiveness, and death will probably be caused by its toxic nature.
Methyl bromide is corrosive, especially toward aluminum, magnesium, and any alloys containing these metals. It is particularly dangerous when in contact with aluminum since it will form an organic-metallic compound that is air-reactive and will begin burning spontaneously.
It will also react with strong oxidizing and reducing agents, mineral acids, caustics, alkali or alkaline earth metals, nitrides, dimethyl sulfoxide, other metals, and organic chemicals such as amines, azo and diazo compounds, and hydrazines. It does not react with water.
NONFIRE RELEASE
Since methyl bromide is toxic, all efforts must be directed at preventing any contact with human life. Not only does this mean control of the vapors, but the liquified product must be prevented from getting into systems that would effect humans by its toxicity or corrosiveness. This means that steps must be taken to prevent its entry into sewers and waterways, among other systems.
Methyl bromide, in its liquified state, may be contained by the construction of containment ponds with the use of diking around the spill with soil, sand, clay, or other materials. A containment pit may be dug near the spill, and the product’s flow may be directed into the pit by digging trenches that lead from the spill to the pit. In either case, the liquid may percolate into the soil, spreading the contamination. Contamination will also spread by contact of the product with the sides of the containment pit or the diking material used in constructing the pond.
In all cases, the actions of the emergency responders in containing the release should be guided by the proper environmental authorities, once it is determined that there is no immediate danger to human life. The environmental authorities will have a better idea of the release’s potential damage to the environment, and fire departments and other emergency responders should realize this.
In other words, the role of first responders at a haz-mat incident should be life rescue; prevention of injury to exposed persons; and prevention of the spread of harm to humans from the original incident scene (containment or stabilization). Once that is accomplished (or simultaneously, if possible), potential damage to the environment must be avoided; decisions regarding this aspect of emergency response are best made by environmental protection specialists. Prevention of property damage is probably now the lowest ranking (but still important) consideration the emergency responders must make.
Once the methyl bromide is contained, remember that this material is actually a gas in liquified form, and when it is released from its container, the product’s temperature may be above its boiling point (38.3°F). This will produce the rapid evolution of methyl bromide gas, which will drift with the wind, hanging close to the ground because of its relatively high vapor density of 3.27. These vapors will travel great distances (unless disturbed by the wind), and accumulate in low places or confined areas. Any unprotected entry into these areas of high concentration of the gas could produce severe injury or death. Evacuation of inhabitants of the area, especially downwind, must always be considered as a tactic.
METHYL BROMIDE
The colorless vapors of methyl bromide can be dispersed by using highpressure water spray or fog patterns, as long as efforts are made to reduce the chance of spread of contamination by containing the runoff. Foam may be applied to try to slow the evolution of vapors, as long as the foam blanket is replenished as it breaks down. Remember that any liquid products of the foam will add to the volume of the liquid being contained. This must be planned for if foam application is the tactical choice.
The liquified methyl bromide should be removed from the containment area and placed into secure containers as soon as possible. This may be done by vacuuming the liquid from the pond or pit with compatible pumping equipment. Whatever contaminated soil remains after the liquid is suctioned up will have to be removed and disposed of under the supervision of the proper environmental authorities and in accordance with federal, state, and local laws. All salvage and clean-up operations should be done by properly educated, properly trained, and properly equipped professionals.
During salvage and clean-up operations, care must be taken to eliminate all ignition sources, and attention must be given to prevent an ignition source from appearing during any exposure to the gas. Even though methyl bromide is considered practically nonflammable by some references, and, as explained earlier, its flammable range may be 10% to 16% (or 13.5% to 14.5%), the fact is that methyl bromide gas will ignite explosively at some concentration between 10% and 16% as long as there is energy sufficient to raise some small portion of the gas to 999°F. All common sources of ignition will provide that energy.
Should the liquid reach a sewer, all downstream receivers of the sewer system must be notified immediately. If the liquid reaches a waterway, all downstream users of the water must be warned that contaminated water may be moving their way. The proper environmental authorities have the equipment, training, education, and experience necessary to take sewage and/or water samples to determine the degree the contamination spread and of the potential danger (or lack thereof) downstream.
The liquid will sink slowly to the bed of a waterway because of its specific gravity of 1.68. It will not “sink like a rock,” but it will eventually make it to the bed of the waterway, unless the current is strong. Once on the bottom, it may continue to move downstream, and collect in deep spots. If this occurs, the stream may be diked and the methyl bromide suctioned from beneath the surface of the water.
If the waterway is small enough, the water may be diverted to a field or other low-lying area adjacent to the stream, and the spilled product may be collected either by suctioning or by the use of an adsorbent material such as activated charcoal. Once the contaminated water is collected and contained, the activated charcoal (carbon) may be mixed with the water. The methyl bromide liquid will adhere to the surface of the carbon, which may then be dredged from the bed of the contained water. Keep in mind that methyl bromide is really a gas, and the liquified methyl bromide, as it boils at temperatures above 38.3°F, will be evolving toxic gas. The activated charcoal, with the methyl bromide adhered to the surface, should be placed immediately into a secure container, since it will be nearly as hazardous as the liquid itself. During all operations involving released liquified methyl bromide, the toxic gas will be evolved.
IDENTIFICATION NUMBERS AND RATINGS
UN/NA
(United Nations/North America)
1062
CAS
(Chemical Abstract Services)
74-83-9
STCC
(Standard Transportation Commodity Code)
4921440
RTECS
(Registry of Toxic Effects of Chemical Substances)
PA4900000
CHRIS
(Chemical Hazard Response Information System)
MTB
EPA RCRA Waste Number
(Environmental Protection Agency Resource Conservation and Recovery Act)
UO29
NFPA 704 Rating
(National Fire Protection Association)
3-1-0
DOT
(Department of Transportation)
Poison B
IMO
(International Maritime Organization)
2.3, poison gas
SYNONYMS
Should the original release of methyl bromide from its container be in the gaseous form rather than the liquid, a dispersal of the gas by a high-pressure spray or fog can be used. If this is not possible and the gas continues to leak (threatening lives because of its toxic nature), a deliberate ignition of the gas may be more desirable than the uncontrolled movement of toxic vapors. This should be done only if it can be determined that there will not be an explosion of the gas upon ignition. Deliberate burns are very radical mitigation techniques, and should be carried out only on the advice of the proper resource people, and executed only under conditions that will reduce the hazard rather than adding to it or producing one more severe.
FIRE SITUATIONS
Liquified methyl bromide will almost always be stored or shipped at temperatures above its boiling point, so the gas is always ready to escape from its container. Even at temperatures below 38.3°F, methyl bromide exhibits a vapor pressure (as do all liquids below their boiling points), which means the liquid will almost always produce deadly or flammable amounts of the gas. Any time heat from impinging flames or radiated heat from a fire or other heat source contacts the methyl bromide container, the liquid will heat up and produce more vapor, until a state of equilibrium exists between the liquid phase and the gas phase within the container. As more heat is absorbed by the container (and consequently, the contents), more and more gas is evolved, causing the pressure within the container to rise. This will continue until either equilibrium is again reached, or the design pressure of the pressure relief valve (if there is one present) is surpassed, at which time methyl bromide gas will be vented to the atmosphere. If the pressure rises faster than the vent can act to relieve it, or the valve malfunctions (or is not present), catastrophic failure of the container will occur when the design strength of the container is surpassed. If this occurs, the escaping gas may ignite, and a resulting explosion, a BLEVE, is possible with methyl bromide.
METHYL BROMIDE
All containers being heated by a fire or other heat source should be cooled from a distance that will provide safety to all personnel in the event of such an explosion. Water should be delivered from as far from the container as possible with the use of unmanned appliances. The radius of evacuation distance depends upon the size of the container. A rail tank car, for example, should cause an evacuation of at least 2,500 feet.
If the threatened container is “out in the middle of nowhere,” (that is, there are no threatened exposures, including human life), no attempt to approach it is necessary. In other words, when there is no life threatened by the possible explosion of the container, there is no need for emergency responders to put their lives in danger. If the environment is threatened (again, the determination must be made by the proper environmental authorities), action can be taken based on the severity of the threat. In recognizing that there may be an explosion, escaping gas may be allowed to ignite. The technique of deliberate ignition may be attempted sooner in this scenario, as long it presents no danger to human life.
PROTECTIVE CLOTHING AND EQUIPMENT
Protective equipment and clothing for use in an incident involving methyl bromide should be selected to prevent the contact of liquid and/or gas with the eyes, skin, or respiratory system. This may include rubber boots, gloves, aprons, the proper face shields, splashproof chemical safety goggles, and positive-pressure, self-contained breathing apparatus. Total encapsulating suits should be worn any time contact with the liquid or gas is possible. Protection from methyl bromide is claimed by some manufacturers of suits made from butyl rubber, neoprene, and Viton. Other manufacturers do not recommend butyl or neoprene. It is of paramount importance that the user of chemical protective suits consult the manufactuer’s recommendations for their particular material.
FIRST AID
In the event of inhalation, the victim must be moved immediately to fresh air and kept quiet and warm. If breathing stops or becomes labored, artifical respiration should be administered in a manner to protect the first-aid provider from the product in the victim’s lungs. Medical attention must be immediate.
For skin contact, all contaminated clothing must be removed and the affected area must be washed with large amounts of water. Immediate medical attention is necessary.
For eye contact, the eyes must be flushed immediately for fifteen minutes, occasionally raising the eyelids. Again, medical attention is required immediately.
If the victim has ingested methyl bromide, he or she must be made to drink a strong solution of salt water. Do not attempt to make an unconscious person drink anything. The victim must not be made to vomit, unless immediate medical attention is not available.
GLOSSARY
Adsorbent—A material that will “pick up” and hold other materials on its surface. Contrast with absorbent.
Alkali metal—A member of Group I on the Periodic Table of the Elements; lithium, sodium, potassium, rubidium, cesium, and francium.
Alkaline earth metal—A member of Group II on the Periodic Table of the Elements; beryllium, magnesium, calcium, strontium, barium, and radium.
Alloy—A physical mixture, usually of metals, created by melting the metals together. Alloys are not chemical compounds.
Equilibrium—Physical equilibrium occurs when two or more physical states or phases are changing at the same rate, with no net change in the system.
Fumigant—A type of pesticide, usually in vapor form, that is used to kill rodents, insects, and unwanted organisms.
Organo-metallic compound—An organic compound that contains a metal attached directly to a carbon atom.
Vapor pressure—The pressure exerted by a vapor on the sides of its container at equilibrium.
