CHEMICAL DATA NOTEBOOK SERIES #80: ISOPENTANE
Isopentane is a flammable, mildly irritating, clear, colorless, liquid hydrocarbon that belongs to the alkane family. It has a low boiling point and an odor similar to gasoline. It is used as a solvent and has replaced foamed polystyrene blowing agents that are harmful to the ozone layer. It also is used to manufacture other chemicals and may be used in the formulation of gasoline because of its very low flash point.
Isopentane has a flash point of 70°F, a flammable range of 1.32 to 8.3 percent in air, and an ignition temperature of 788°F. It has a specific gravity of 0.62, a molecular weight of 72, and a vapor density of 2.5. It boils at 82°F, freezes at – 256°F, and is not soluble in water. Its molecular formula is which sometimes is written (CH,)2CHCH2CHJ.
Isopentane is an isomer of pentane (also known as n-pentane or normal pentane). An isomer is one of two or more chemical compounds with the same molecular formula but a different structural formula. Isopentane contains exactly the same amount of carbon and hydrogen as pentane, but the two compounds are arranged slightly differently. The difference is enough to provide some changes in properties between pentane and isopentane. These properties are listed in the box below, which includes the properties of a third isomer, neopentane.
Isopentane, neopentane, and pentane have the same molecular formula, molecular weight, and vapor density. Some of the differences between them may seem insignificant, but they just might mean the difference between a devastating explosion and the safe mitigation of an incident.
The principal hazard of isopentane is its flammability. Its flash point is so low that vapors sufficient to form an ignitable mixture with the air near the surface of a spill of isopentane will be present at all ambient temperatures. Its very low ignition temperature can be reached by all common ignition sources. This combination of very low flash point and very low ignition temperature means that ignition of any released vapors is an almost certainty. Its vapor density of 2.5 means that its vapors, whether released from a leaking container or a pool of liquid, will sink to the ground, stay together in an invisible vapor cloud, and flow (vapors are fluids) down any low spots in the terrain until they encounter an ignition source. The result will be an explosion of the vapors, with the explosion and flames “flashing back” to the vapor source.
The only fairly “safe” property of isopentane is its relatively narrow flammable range, representing a spread of only seven percent. This narrow flammable range means that the vapors of isopentane may build rapidly in concentration (because of its volatility) and may surpass its upper flammable (or explosive) limit quickly, thus becoming too rich for ignition. The “best” fuels are those with low flash points, low ignition temperatures, and narrow flammable ranges. Isopentane’s properties fit these general properties very well, although an even narrower flammable range would make it ideal.
Generally, the saturated hydrocarbons, of which isopentane is an example, are nontoxic. However, as the molecule gets bigger, some low-tomoderate degree of toxicity apparently develops. Isopentane has a TLVTWA (threshold limit value-time weighted average) of 119 ppm (parts per million of air) and an STEL (shortterm exposure limit) of 610 ppm. These levels are moderately high when compared with truly toxic materials.
Avoid repeated exposure to high concentrations of the vapors or to the liquid itself. Repeated contact of isopentane with the skin causes reddening, irritation, and cracking due to the material’s defatting action on body fat. Contact with the eyes can cause moderate irritation. Exposure to high concentrations of isopentane can cause breathing difficulties, coughing, irritation of the nose and throat, and eventually unconsciousness. Ingestion of isopentane can cause depression, headaches, nausea, swelling of the abdomen, and vomiting. Inhaling isopentane vapors can cause lung irritation and pulmonary edema on a delayed basis.
Isopentane is considered a stable chemical, but under some conditions it will react violently with all strong oxidizers. The class of hazardous materials called oxidizers includes all chemicals that contain oxygen, which they readily give up. But since anything that will support combustion is an oxidizer, this hazard class also includes the halogens (fluorine, chlorine, bromine, and iodine). Since isopentane is an excellent fuel, once it is mixed with a strong oxidizer the only missing “leg” of the fire triangle is the energy leg. This can be provided in the form of an open flame, a spark, an electrical discharge, heat caused by friction, or simply the energy input by the sun or a man-made light source. Once the energy input has heated some small portion of the vapors of isopentane to its ignition temperature, an explosion will follow.
Isopentane is not corrosive to metals, but it may attack plastics, rubber, and some other polymeric coatings by its solvent action.
Because of the volatility of isopentane and the vapor density of its vapors, consider immediate evacuation downwind of the release. The evacuation distance should be a minimum of ‘A mile from the release and should extend to a mile in the event of a large release. The evacuation distance downwind should be a minimum of one mile (two miles for large releases).
Consider any large release of isopentane a major hazardous-materials incident. Although isopentane is not particularly toxic, corrosive, or reactive, it is a major hazard because of the flammability, volatility, and explosiveness of its vapors when ignited in large quantities. Such a release should activate the community’s emergency response plan as dictated by SARA (Superfund Amendments and Reauthorization Act of 1986) Title III.
Approach from upwind, and eliminate all ignition sources. Limit the spread of isopentane by constructing containment ponds and pits. Use nonsparking tools and equipment when working near released isopentane.
Do not allow isopentane to enter any sewers or waterways. If any of the product does enter a sewer, evaporation will produce large volumes of heavier-than-air explosive vapors, which then will spread slowly throughout the system. Any vapors that subsequently escape from the sewer system at any catch-basin or manhole quickly will enter the flammable range and become capable of producing an explosion along the entire sewer line. Notify all connected sewage treatment facilities immediately of the presence of isopentane in the system.
If isopentane enters a river, stream, lake, or pond, it will float on the surface and spread into a film, evaporating as it does so. Because of its vapor density, the vapors may accumulate over the surface of stationary water and within the banks of moving water. The vapors may be too rich to ignite right near the surface of the water, but they will be within the flammable range somewhere near the edge of the invisible vapor cloud. This is where the explosive ignition of vapors is likely to occur.
Slow the evolution of vapors by covering the surface of the contained product with a cover made from compatible material or by applying firefighting foam.
Notify all downstream users of the water immediately of the contamination. Extremely dangerous conditions will exist anywhere downstream where an industrial operation may draw water in from the river or stream to cool its process equipment. Explosive vapors will be present in large quantities as soon as the w ater is heated slightly by the hot equipment, and there are usually many ignition sources within the average industrial plant that does not handle flammable liquids.
If it is possible, divert moving water into a low-lying area until it can be decontaminated. It may be necessary to divert only the top few’ inches of water, since this is where the isopentane will be.
Isopentane also may be removed from the waterway with floating booms, floating barriers, or skimming devices such as those used to skim spilled oil. The material then should be suctioned off and transported to secure containers. Barriers may be constructed on the surface using compatible netting, holding peat moss or straw’, on the upstream side of the barrier. Properly trained, educated, and equipped professional salvage crews will dispose of contaminated barrier materials in the same manner as they would absorbent materials used on land.
Once the material is contained, it may be salvaged by suctioning or pumping the isopentane from the pond or pit wfith compatible equipment (the metal in the equipment must be nonsparking, and the gaskets and other polymeric parts must be resistant to the solvent power of the isopentane). Any material left in the pond or pit may be removed using absorbents such as clay, peat moss, sand, sawxlust, soil, or other commercial sorbents. This work should be done by a professional salvage firm, the shipper, or the seller of the isopentane—never by the fire department. The contaminated sorbent must be handled carefully, since it will have the same properties as the isopentane, and it must be disposed of according to all federal, state, and local regulations. The environmental experts mobilized by the emergency plan will determine when the water is no longer contaminated.
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
(International Maritime Organization)
3.1, flammable liquid
Isopentane vapors may be dispersed into the air (and out of its flammable range) with high-pressure sprays or water fogs. Dispersing techniques must be carried out carefully, since it is possible to produce a static discharge caused by the movement of water through the hose and the air. Contain all runoff water.
If containers of isopentane are exposed to the radiated heat of a fire or impinging flames, keep them as cool as possible by applying water with unmanned appliances from as far away as possible. Any heated containers can fail catastrophically due to overpressurization. If safety relief devices are present and functioning, the released vapors may be burning. Do not extinguish these flames unless the flow of fuel can be stopped immediately after extinguishment.
Pools of burning isopentane can be extinguished using carbon dioxide, dry chemicals, foam, or water delivered as a spray or fog, depending on the amount of burning isopentane, the amount of extinguisher available, and weather conditions. Straight water streams may spread the isopentane, consequently spreading the fire.
Once a pool of burning isopentane is extinguished, explosive reignition is still possible. This can occur if the fire has heated a piece of metal to a temperature above the ignition temperature of isopentane, which is relatively low. If the fire is extinguished and the metal has not been cooled below 788°F, the isopentane vapors will reignite if they are within the flammable range.
When it burns, isopentane, like other hydrocarbon liquids, produces large amounts of carbon monoxide. This means firefighters must wear respiratory’ protection even when fighting fire outside. Respiratory protection should be worn by all personnel on the fireground during any fire, inside or out, as well as during all overhaul procedures.
PROTECTIVE CLOTHING AND EQUIPMENT
Protective clothing and equipment should prevent contact of the material with the skin and eyes. This requires materials that are impervious to isopentane and that will not absorb it. Nitrile rubber gloves and boots, chemical splashproof goggles, and face shields may suffice. Compatible materials include nitrile rubber, polyethylene/polyvinyl alcohol, polyvinyl alcohol, and Viton®. Consult manufacturers of protective clothing. Respiratory protection in the form of positive-pressure, self-contained breathing apparatus is required.
For inhalation, move the victim to fresh air, and keep him/her calm and warm. If the victim’s breathing has stopped or has become labored, administer artificial respiration, being aware that such action might expose the first-aid giver to the material in the victim’s lungs and/or vomit. Seek immediate medical attention.
For eye contact, flush the eyes immediately for at least 15 minutes, lifting the eyelids occasionally. Medical attention is required if irritation persists after flushing.
For skin contact, wash the affected body areas with large amounts of soap and water. If irritation continues after washing, seek immediate medical attention.
For ingestion, do not induce vomiting. Keep the victim warm and calm, and seek immediate medical attention.