CHEMICAL DATA NOTEBOOK SERIES #104: PROPYLENE OXIDE
BY FRANK L. FIRE
Propylene oxide is a flammable, toxic, irritating, highly volatile, colorless liquid with a sweet odor resembling alcohol and ether. Its odor may be detected at levels as low as 10 ppm (parts per million of air). It is used to manufacture brake fluids, detergents, fumigants, propylene glycol, ingredients of polyurethane foam, and synthetic lubricants. There is some evidence that propylene oxide may be a carcinogen.
PROPERTIES
Propylene oxide has a flash point of -37°F, an explosive (flammable) range of from 2.1 to 38.5 percent in air, an ignition temperature of 840°F, a specific gravity of 0.83, a molecular weight of 58, a vapor density of 2.0, a boiling point of 93.7°F, and a freezing point of -169.4°F. It is soluble in water. Its molecular formula is C3H6O or CH3CHOCH2.
HAZARDS
Propylene oxide`s major hazard is flammability: It has a very low flash point, a low ignition temperature, and a wide explosive (flammable) range. In addition, it is highly volatile–it evaporates rapidly, producing vapors sufficient to form an ignitable mixture with the air at a very low temperature. This, of course, is the definition of “flash point,” which in propylene oxide`s case is -37°F. At all ambient temperatures around the world (with the possible exceptions of Antarctica, some parts of Siberia, and Grand Forks, North Dakota), propylene oxide will produce sufficient vapors to ignite and explode.
Propylene oxide`s low ignition temperature of 840°F can be reached easily by all common ignition sources, and its wide explosive range of 2.1 to 38.5 percent in air means that almost any release will immediately produce an explosive situation. All of this translates into making propylene oxide a very dangerous material when released.
Also a toxic material, propylene oxide has a TLV-TWA (threshold limit value-time weighted average)–established by the American Conference of Governmental Industrial Hygienists (ACGIH)–of 20 ppm over each eight hours of a 40-hour workweek. The Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) has also been set at 20 ppm. The major toxicity hazard is inhaling the relatively high vapor concentrations that may be present in air. Direct contact with the material also must be strictly avoided.
Inhaling the vapors may cause coughing and irritation of the eyes, nose, throat, and lungs. High concentrations in air may cause central nervous system depression with symptoms that include difficulty in breathing and coordination, headache, nasal discharge, nausea, vomiting, weakness, unconsciousness, and possibly death. Aspiration, resulting in lung damage, may occur during swallowing or vomiting.
Should propylene oxide vapor or liquid contact the eyes, it will cause irritation, considerable pain, excessive blinking and tear production, excessive redness, swelling, and possible injury to the cornea. The liquid will cause more severe irritation, with chemical burns to the eye, producing possible irreversible damage.
Prolonged or widespread skin contact may result in the absorption of potentially harmful amounts of material. Contact with the skin will cause irritation, blistering, and burns on short exposure, especially when the product is confined to the skin by contaminated jewelry or clothing.
Ingesting liquid propylene oxide may irritate and burn the mouth and gastrointestinal tract as well as cause several of the symptoms of vapor inhalation.
Considered a stable material, propylene oxide does not react with water. However, it reacts violently with amines, acidic alcohols, anhydrous metal chlorides, iron, strong acids (such as hydrochloric acid, sulfuric acid, and nitric acid), strong bases, copper or copper alloys, peroxides, alkali metal hydroxides, ammonia, chlorine, other oxidizing materials, and various oxides and chlorides. It also will attack some forms of plastics, rubbers, and polymeric coatings.
Under certain conditions, propylene oxide will polymerize (a chemical reaction possible only with chemical compounds called “monomers” that release large quantities of heat energy, which often results in a violent explosion), particularly when in contact with highly active catalytic surfaces such as the anhydrous chlorides of aluminum, iron, and tin; peroxides of iron and aluminum; alkali metal hydroxides; and clay-based absorbents. Anhydrous means that the chemical has no water present; the common alkali metals are lithium, sodium, and potassium.
Propylene oxide is slightly corrosive and may react violently on contact with acetylide-forming metals such as copper and its alloys.
NONFIRE RELEASE
A release of propylene oxide should be treated with considerably more caution than a spill of gasoline. Although gasoline may have a slightly lower flash point (-45°F vs. -37°F for propylene oxide), propylene oxide is several times more hazardous and many times more toxic and reactive than gasoline. Moreover, it also has the capability to polymerize. Propylene oxide`s explosive range is many times wider than that of gasoline, and its ignition temperature is also lower. All in all, although a release of propylene oxide should be handled in the same manner as releases of many other flammable liquids, the incident commander must be concerned about considerably more hazards.
If propylene oxide is leaking but is not on fire, approach it from upwind and uphill, eliminate all ignition sources, and exclude all unauthorized personnel from the danger zone. All emergency personnel must wear the proper protective clothing. Immediately consider evacuation within a minimum radius of 2,500 feet–or larger areas if downwind.
The explosive ignition of propylene oxide vapors is the major danger to life; therefore, exercise care near the spill and within the immediate areas to which the vapors might spread downwind. Propylene oxide`s vapor density of 2.0 means that (with no appreciable breeze present) the vapors will hug the ground and flow downhill and along low spots and may accumulate in such low-lying areas or in confined spaces, producing concentrations above the level that causes severe eye and nose irritation–possibly even reaching the lower flammable limit. Always consider evacuation of the area downwind–and an area up to one-half mile around the source of vapors and further downwind (depending on the size of the leaking container).
Emergency responders always must keep in mind that a fire usually is the second reaction produced by the ignition of flammable vapors; the first is explosion of the vapors.
If the liquid leaking from a container can be captured in a container, this technique should be tried, since the liquid, once captured, then can be transferred to a secure container. Use only sparkproof/explosionproof tools, pumping equipment, lights, fans, and electrical equipment.
If the leaking liquid cannot be captured in a portable tank or some other type of container, its spread should be prevented by capturing it in a containment pond constructed by pushing dirt, sand, or some other absorbent material into a diking configuration around the spill. Do not use clay; propylene oxide may react violently with it. If the proper equipment is available, a containment pit or pond of a size sufficient to hold the amount of material involved (and whatever may result from the mitigation techniques available) may be dug.
Dilution is one mitigation technique option. This process involves adding water to increase the flash point of the resulting solution so that the temperature at which vapors sufficient to form an ignitable mixture with the air will be considerably higher than ambient temperatures. This technique can be used only if the containment pond or pit is large enough to contain the added volume that results. Since pure propylene oxide has a flash point of -37°F, it may not be possible to raise it high enough to be effective unless the amount of leaked product is small and the containment area is large.
Applying alcohol-type foam or aqueous film-forming foam (AFFF) to the surface of the liquid may slow down the evolution of vapors. The foam layer may have to be replenished from time to time as it breaks down, and the resulting added volume–as well as all other runoff water or dilute solutions–must be contained.
Some type of impervious material may be used to cover the contained liquid. This technique is easier to use for a small pit rather than a large pond. Also, the evolution of vapors in a pit is slower than in a pond, since the rate of evaporation is lower with a smaller surface area of the liquid exposed to the atmosphere.
Another option is to use high-pressure water spray or fog to sweep the propylene oxide vapors from the air. The vapors will be dispersed or dissolve in the spray or fog; the runoff water must be contained, of course.
Once the product has been properly contained, professional cleanup crews may use explosionproof equipment to pump or suction the product from a container or the containment pond or pit into secure containers. Only properly educated, trained, and equipped personnel provided or paid for by the manufacturer of the spilled product, shipper, or buyer should do this work. Firefighters and most other emergency response personnel should not be involved in salvage or cleanup operations.
Once the product is in secure containers, any remaining liquid may be absorbed by using cement powder, earth, fly ash, sand, sawdust, soil, commercial products, or any other available absorbent material. The resulting sorbent containing propylene oxide must be handled just as safely as the original material and must be disposed of in accordance with federal, state, and local regulations. The environmental authorities will determine how much soil will have to be removed and disposed of in the same manner as the soaked sorbent.
All released product must be prevented from reaching a sewer or waterway. Product entering a sewer system can spread flammable vapors and pose the threat of a citywide explosion via the sewer system. Should product enter the sewer system, immediately warn all sewage treatment facilities.
If the propylene oxide enters a stream or other waterway, immediately warn all downstream users of the water. The toxicity of the product and its effect on fish, waterfowl, and other wildlife depend on the amount of the product entering the waterway, the volume of water, and the rate at which the water is moving. The product will dissolve in the waterway, especially if the water is moving fairly rapidly. If the waterway can be diverted into a low-lying area by use of a temporary dam, the propylene oxide can be removed by aeration techniques. The same techniques can be used if the product enters a pond or lake.
If the waterway is fast-moving, the product will be diluted fairly rapidly and all resulting dangers may be removed (unless the volume of the spilled product is very large). However, this can be determined only by testing the water at different points downstream; testing must be done by trained personnel under the supervision of environmental agency personnel. Water treatment plants–if properly and timely warned and properly equipped– may be able to remove the contamination, but do not take the chance. If heavily contaminated water enters an industrial intake and contacts hot equipment (the reason water is taken in in the first place), the vapors of the product driven out of solution by the process heat might produce vapors sufficient to produce an explosion.
In a slow-moving waterway or in lakes and ponds, adding activated carbon or peat moss to the contaminated water, followed by effective mixing, may capture spilled product that has dissolved in water. Adsorbent materials later may be removed by mechanical means.
FIRE SCENARIO
If a container of propylene oxide is heated by radiant heat or impinging flame, there is always the possibility of catastrophic container failure and the releasing of flammable liquid and vapors–probably explosively. Whenever possible, a container stressed by heat should be cooled by as much water as can be delivered safely to the container, preferably by unmanned monitors.
According to many references, carbon dioxide, dry chemical, alcohol foam, and water spray may be used to fight the fire. The choice of extinguishing agent depends on factors such as the amount of propylene oxide released, the location of the release, weather conditions, the “lay of the land,” and the amount of extinguishing agent available. Water may be ineffective as an extinguisher but may be used to dilute spills to nonflammable mixtures.
If the propylene oxide vapors from a release have traveled some distance and have been ignited, they will explode and “flash” back to the spill area. Even after burning propylene oxide has been extinguished, the vapors of the hot propylene oxide could reach the explosive range again and cause another explosion. In certain special cases, as when there is no danger to life, exposure, or the environment or systems, it may be wise to allow a controlled burn until the fuel has been consumed.
If the fire is the result of a leak from a container that is still leaking and is exposed to the fire, another set of problems is produced. Although technically a BLEVE (boiling-liquid, expanding-vapor explosion) will not occur with a flammable liquid, there is always the danger of overpressure in the leaking container caused by flame impingement or radiant heat that will result in the container`s rapid failure, releasing large amounts of hot fuel that will vaporize fast enough to cause an explosion resembling a BLEVE. The volatility of propylene oxide is such that tremendous volumes of vapors will be produced and could cause this overpressurization. Whatever the mechanism of the explosion, it will be serious enough to cause death and injury to anyone in the vicinity.
In many cases, it may be wise not to extinguish the fire until the flow of product can be stopped, just as is done in a fire involving a leaking gas. This, of course, will prevent the previously mentioned reignition (an explosion). Any closed container exposed to heat may suffer a pressure-relief explosion and, depending on the container`s size and shape (such as 55-gallon drums), will rocket into the air, trailing burning propylene oxide behind it. Larger containers may or may not leave the ground, but the resulting pressure-relief explosion and dispersal of burning liquid (and the rising fireball) will produce proportionately larger devastation. The implication here is to try to cool all containers exposed to the heat, including those behind you that may be experiencing the energy of radiant heat. Firefighters should never get between a fire and containers holding gases and liquids, whether flammable or not.
PROTECTIVE CLOTHING AND EQUIPMENT
Protective clothing and equipment should prevent any reasonable probability of eye contact and any possibility of skin contact with the spilled propylene oxide. Protective gear may include rubber boots, gloves, face shields, splashproof safety goggles, and other impervious and resistant clothing. Total encapsulating suits with self-contained breathing apparatus (SCBA) may be advisable in some cases to prevent contact with high vapor or fume concentrations in air. The references differ with regard to the compatible materials that may be used in the construction of total encapsulating suits. Consult manufacturers of propylene oxide and total encapsulating suits about which materials will provide the best protection.
FIRST AID
Inhalation of vapors. Move the victim to fresh air and keep him warm and at rest. If breathing becomes difficult or has stopped, administer artificial respiration. Administering mouth-to-mouth resuscitation may expose the first-aid provider to the chemical in the victim`s lungs or vomit. Get immediate medical attention.
Eye contact. Immediately flush the eyes with water for at least 20 minutes. Hold eyelids apart while flushing, to rinse the entire surface of the eye and lids. Always seek medical attention.
Skin contact. Wash the skin with plenty of soap and water until all traces of material have been removed. Remove and clean contaminated clothing and shoes. Seek immediate medical attention.
Ingestion. If the patient is conscious and can swallow, administer two glasses of water, but do not induce vomiting. Never give anything by mouth to an unconscious or convulsing person. Keep the victim warm and at rest. Get immediate medical attention.
SYNONYMS
epoxy propane
1,2-epoxypropane
2,3–epoxypropane
methylethylene oxide
methyl oxirane
NCI-c50099
oxirane, methyl-
propene oxide
propylene epoxide
1,2-propylene oxide
IDENTIFICATION NUMBERS AND RATING
CAS
(Chemical Abstract Services)
75-56-9
STCC
(Standard Transportation Commodity Code)
4906620
RTECS
(Registry of Toxic Effects of Chemical Substances)
TZ2975000
UN/NA
(United Nations/North America)
UN1280
CHRIS
(Chemical Hazard Response Information System)
POX
DOT
(U.S. Department of Transportation)
Class 3, flammable liquid
NFPA 704 Rating
(National Fire Protection Association)
2-4-2
IMO
(International Maritime Organization)
3.1, flammable liquid
FRANK L. FIRE is the vice president of marketing for Americhem Inc. in Cuyahoga Falls, Ohio. He is 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.
