CHEMICAL DATA NOTEBOOK SERIES #117: HEXANE
BY FRANK L. FIRE
Hexane is a flammable, volatile, irritating, slightly toxic, clear, colorless liquid with an odor similar to gasoline. A pure substance that may be used as an ingredient in gasoline, it is used principally as a solvent, an extractant, and a medium in which chemical reactions are carried out to produce pharmaceuticals and polymers. It is also used in the manufacture of many materials such as adhesives, food additives, inks, lacquers, stains, and thermometers.
Hexane is a pure compound, a member of the analogous series of compounds known as the alkanes. It is a saturated hydrocarbon, meaning it has no double covalent bonds between its carbon atoms. As a hydrocarbon, it is not soluble in water or perhaps very slightly soluble. Its molecular formula is C6H14.
Hexane has a flash point of -7°F, an ignition temperature of 437°F to 835°F, and an explosive (flammable) range of from 1.1 to 7.7 percent. This narrow explosive range is one of the properties that makes it an ideal gasoline additive. The narrower the explosive range of a gas or the vapors of a flammable or combustible liquid, the (relatively) less hazardous and the better a fuel it is. Hexane has a specific gravity of 0.73, a molecular weight of 86, and a vapor density of 2.97. It boils at 155.7°F, freezes at -139°F, and is insoluble in water.
Flammability is hexane`s major hazard, and its properties reinforce that. Its low flash point means it will produce vapors sufficient to form an ignitable mixture with the air near the liquid or container`s surface at temperatures of -7°F and higher. Therefore, in any setting in which hexane is used and the temperature is -7°F or higher (as it would be in any industrial setting), an explosion will occur if enough vapors have accumulated and a proper ignition source is present.
With such a high vapor density of almost 3.0 (air`s average vapor density is 1.0), vapors from a spill or other release will sink to the ground and flow (gases and vapors are fluids) along any depressions–always downhill and seemingly looking for an ignition source–at which time the vapors will ignite explosively and “flash” back to the vapor source, where another explosion may occur due to the vapor accumulation.
An explosion is the first reaction when flammable gases or flammable or combustible liquid vapors are ignited within their explosive ranges–hence the tendency for some to think of this range as explosive instead of flammable. Too often, emergency responders think that these gases and vapors will simply burn when first ignited. The resulting explosion (the strength of which is determined by the amount of vapors in the air), however, can be fatal to anyone making this mistake.
Hexane`s relatively low ignition temperature of 437°F is well within the range of all common ignition sources, even a smoldering cigarette. The narrow flammable range means that the vapors may be too rich to burn near the surface of the spilled liquid, but the high vapor density means the vapors will “hang together” for a long time, flowing along low spots in the terrain “looking” for an ignition source.
A very volatile material, hexane has a very high evaporation rate, and explosive vapors will be rapidly generated at all ambient temperatures. The flash point of the liquid is very low (-7°F), and enough explosive vapors will be in the air at all temperatures above -7°F when enough energy is present to raise just a small amount of the vapors to 437°F. The tiniest of sparks or the slightest friction could cause ignition.
Hexane is considered a very stable material. It will not react with many chemicals. It, however, will react violently or explosively with all strong oxidizers. Its solvent nature also will cause it to dissolve some rubbers, plastics, and polymeric coatings.
Although hexane is considered only slightly toxic, its toxic hazard should not be overlooked. Its TLV-TWA (threshold limit value-time weighted average) is 50 ppm (parts per million of air), and its STEL (short-term exposure limit) is 176 ppm.
Some hexane may be sold with small amounts of benzene present. Repeated contacts of such liquid with the skin may cause irritation and redness due to its defatting action, and some individuals may develop hypersensitivity.
Contact with the eyes usually will cause irritation and perhaps only temporary injury.
Inhaling the vapors may irritate the eyes, nose, and respiratory tract and depress the central nervous system. Low concentrations can cause dizziness, headache, and mental confusion; high concentrations can cause convulsions, unconsciousness, coma, pulmonary edema, and death from asphyxiation or respiratory failure. Other organs, including the pancreas, liver, and kidneys, also may be damaged.
Ingestion can cause irritation of the mouth, swelling of the abdomen, headache, and depression of the central nervous system. Aspiration into the lungs can result in severe lung irritation, producing pulmonary edema and pneumonitis. If benzene is pres-ent, there is the additional hazard of carcinogenicity.
When hexane is released accidentally, follow the same procedures as those used for safely handling incidents involving other hydrocarbon flammable liquids. As a matter of fact, many of the procedures the fire service uses in handling flammable liquid spills were developed from reports of its experiences with gasoline spills.
Always approach a hexane spill or release from upwind and uphill, and immediately eliminate all ignition sources. Keep all unauthorized personnel from entering the area, and prevent all bodily contact with the liquid. Make respiratory protection mandatory.
Prevent hexane from entering sewers and waterways by blocking catch basins and other entryways to sewers and containing the liquid in ponds or pits. Ponds can be constructed by building dikes of soil, sand, clay, or other absorbent materials that may be present, and containment pits and trenches to lead the liquid to the pit may be dug. In all cases, use sparkproof tools and explosionproof equipment to avoid igniting the explosive vapors. A containment pit is more desirable than a pond because the pit probably will have a smaller surface area. One of the variables controlling the evolution of liquid vapors (evaporation rate) is the surface area of the liquid interfacing with the atmosphere. All other factors (temperature, pressure, and so on) being equal, the larger the surface area, the higher the rate of evaporation. Mitigation techniques such as covering the surface with a tarpaulin and blanketing it with foam are more feasible when the surface area is small. If sheets of polymeric material (rubber or plastic) are used to cover the hexane surface, run tests to determine the material`s compatibility with the product.
Firefighting foam is fairly effective in reducing vapor evolution, even with a low flash point liquid like hexane. However, the foam may break down, and reapplication may be necessary. As the foam breaks down, it will add to the volume of the contained liquid and could cause a runoff, which also will have to be contained. A fine water spray or fog may be used to accelerate the dispersal of vapors immediately downwind of the spill. This water, which may be contaminated with hexane, must be contained; any spray used in dispersal may add to the volume of the contained product.
In all cases, when dealing with an accidental release of hexane, contained or not, immediately consider evacuating local and downwind areas. If the liquid should enter a sewer or waterway and containment by damming or diking or diverting the water is not possible, immediately notify all downstream users of the water and operators of sewage treatment facilities. Disastrous explosions could occur if water contaminated with hexane is used for an industrial operation.
With its specific gravity of 0.73 (the specific gravity of water is 1.0) and its insolubility in water, hexane will float on the water`s surface. It, therefore, may be skimmed off the top of a lake or slow-moving stream by conventional floating booms and then suctioned into secure containers. It may be possible to dam or dike a waterway and divert the hexane into a containment area, where it can be removed. Again, all tools and equipment must be sparkproof and explosionproof and the containment area must be evacuated.
Contained hexane may be absorbed with clay, soil, sand, fly ash, cement powder, peat moss, straw, and most other commercial sorbents. After the material has been absorbed, the product still is a hazardous flammable liquid and must be handled as carefully as the spilled product. Qualified professionals operating in accordance with all the safety rules and within all federal, state, and local regulations should dispose of the material. Environmental authorities must oversee the cleanup, and their instructions must be followed.
Hexane in containment ponds and pits will soak into the soil and spread contamination underground. At the first indication of a spill of hexane or other hazardous material, notify the proper environmental authorities, who must have the final word on how the cleanup procedure should be carried out. They will determine how far contamination may have spread.
Qualified professionals–not firefighters–should clean up at hazardous-materials incidents unless, of course, the firefighters have been properly educated, trained, and equipped for the task. Cleanup may be every bit as hazardous as mitigation, and most fire departments are not qualified to do it.
When a tank truck or other container of hexane not involved in fire is threatened by flames or radiant heat, keep the truck or container as cool as possible by applying water with unmanned appliances positioned as far away as possible. As the container is heated, catastrophic failure can occur if excess pressure is not vented away. Hexane tank trucks ordinarily are not subject to a BLEVE (boiling-liquid, expanding-vapor explosion), since, like gasoline tank trucks, the aluminum tank usually will melt or burn away, relieving the pressure. However, if conditions are “just right,” the container may rupture, and the resulting explosion and fire could be as devastating as a BLEVE.
Most fire departments have responded to gasoline fires and therefore have experience in handling emergencies involving similar flammable liquids such as hexane burns. Great strides have been made in using water, which at one time was forbidden because it displaced the burning flammable liquid and carried it beyond the fire scene. New nozzles and delivery techniques that present the water to the fire as a fine spray or fog have made it possible to control “normal” fires involving flammable liquids. Note: The vapors evolved from the liquid, not the liquid, burn. If evolution of the vapors can be slowed, the fire may be controlled sooner. Also, any metal exposed to the liquid and heated by the fire may be the source of the fire`s explosive reignition after extinguishment. Always be aware of the potential for reignition when dealing with hexane or similar products such as pentane, heptane, octane, nonane, and gasoline.
PROTECTIVE CLOTHING AND EQUIPMENT
Choose protective clothing and equipment that will prevent hexane liquid or vapors from contacting the eyes, skin, and respiratory system. Wear splashproof chemical goggles and a face shield and use positive-pressure self-contained breathing apparatus. Rubber boots, gloves, and aprons and other impervious clothing offer protection. Some manufacturers of total encapsulating suits claim that chlorinated polyethylene, neoprene, nitrile-butadiene rubber, nitrile rubber, polyurethane, polyvinyl alcohol, and Viton® will offer protection. At least one other reference claims that only nitrile rubber, polyvinyl alcohol, Teflon®, and Viton® offer protection. Contact the manufacturers of total encapsulating suits and hexane for their recommendations.
Inhalation of vapors. Move the victim to fresh air. Keep him/her calm and warm. If breathing has stopped or becomes labored, administer artificial respiration. Be aware that such action might expose the first-aid giver to the material in the victim`s lungs or vomit. Immediate medical attention is needed.
Eye contact. Flush the eyes immediately for at least 20 minutes, lifting the eyelids occasionally. Immediate medical attention is necessary if the irritation remains after flushing.
Skin contact. Remove contaminated clothing and wash the affected body areas with large amounts of soap and water. If the irritation continues after washing, immediate medical attention is needed.
Ingestion. Keep the victim calm and warm. Do not induce vomiting. Get immediate medical attention. n
IDENTIFICATION NUMBERS AND RATINGS
(Chemical Abstract Services)
(Standard Transportation Commodity Code)
(Registry of Toxic Effects of Chemical Substances)
(United Nations/North America)
(Chemical Hazard Response Information System)
(U.S. Department of Transportation)
NFPA 704 Rating
(National Fire Protection Association)
(International Maritime Organization)
3.1, flammable liquid
n 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.