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Propylene Oxide Chemical Backgrounder


Propylene oxide (C.A.S. 75-56-9) is a colorless liquid with an ether-like odor that is used mainly (60%) as a chemical intermediate in the production of polyurethane polyols, which are used to make polyurethane foams, coatings, and adhesives. It is used (20%) in the manufacture of propylene glycol, which is used in fiberglass-reinforced plastics, foods, cosmetics, pharmaceuticals, cigarette tobacco, packaging materials, dyes, and hydraulic fluids. It is also used in the preparation of glycol ethers (3%), dipropylene glycol (2%), industrial polyglycols, lubricants, surfactants, oil demulsifiers, isopropanolamines, and as a solvent and soil sterilant (6%). It is used in fumigation chambers for the sterilization of packaged foods; as a stabilizer for methylene chloride, fuel, and heating oils; in treating wood for termite resistance; as an acid scavenger and pH control agent; for removing residual catalysts from crude polyolefins; in fuel-air explosives in munitions; and as a component of Zeospan, a polyether rubber.

Chemical properties:

Propylene oxide is a volatile, flammable liquid that is soluble in water, alcohol, and ether. It is highly dangerous when exposed to heat or flame. It has a violent reaction with hydrogen chloride, chlorosulfonic acid, hydrogen fluoride, and oleum. It should not be stored in the presence of acids, bases, chlorides of iron, aluminum, and tin, or peroxides of iron and aluminum; any of these may cause violent polymerization. Propylene oxide is miscible with most organic solvents, and forms a two-layer system with water. It is incompatible with anhydrous metal chlorides, iron, strong acids, caustics, and peroxides, and reacts vigorously with oxidizing materials. When exposed to flame, propylene oxide will burn with a hot flame like isopropyl if not confined, but it may explode if confined. Polymerization may occur due to high temperatures or contamination with alkalis, aqueous acids, amines, and acidic alcohols.

Synonyms for propylene oxide are epoxypropane; 1,2-epoxypropane; methyl ethylene oxide; methyl oxirane; propene oxide; and 1,2-propylene oxide.

Derivatives of propylene oxide are polyether polyols; propylene glycol; di- and tripropylene glycol; poly (propylene glycol)s; surfactants; glycol ethers; and isopropanolamines.


  • Chemical Name: Propylene Oxide
  • Regulatory Name: Propylene Oxide
  • Formula: C3H6O
  • DOT Label: Flammable Liquid
  • CAS: 75-56-9
  • STCC: 4906620
  • UN Number: 1280

Health effects:

Propylene oxide is classified as a substance which may reasonably be anticipated to be a carcinogen, according to the Sixth Annual Report on Carcinogens, published by the National Toxicology Program, U.S. Department of Health and Human Services. It is also classified as a carcinogen in EPA’s Toxic Release Inventory (TRI). If it is inhaled or ingested, or makes eye or skin contact, it can irritate the eyes, upper respiratory system, lungs, and skin.

Exposure Values:

  • IDLH: 400 ppm; Not applicable for Propylene oxide, a potential human
  • carcinogen (NIOSH, 1997)
  • TLV TWA: 5 ppm Confirmed animal carcinogen (ACGIH, 1999)
  • ERPG-1: 50 ppm (AIHA, 1999)
  • ERPG-2: 250 ppm (AIHA, 1999)
  • ERPG-3: 750 ppm (AIHA, 1999)
  • OSHA PEL: TWA 100 ppm (240 mg/m3)


U.S. manufacturers of propylene oxide are Dow Chemical Co, Midland, MI; Freeport, TX; and ARCO Chemical Co, Philadelphia; Bayport, TX.


The Occupational Safety and Health Administration (OSHA) issues permissible exposure limits for propylene oxide; that eight-hour time-weighted average (TWA) limit is 100 ppm. It also regulates propylene oxide under the Hazard Communication Standard and as a chemical hazard in laboratories.

EPA regulates propylene oxide under the Clean Air Act, Clean Water Act, Comprehensive Environmental Response, Compensation, and Liability Act; Food, Drug, and Cosmetic Act; Resource Conservation and Recovery Act; and Toxic Substances Control Act.

The Food and Drug Administration regulates propylene oxide as an indirect food additives in products which may come into contact with food and as an adjuvant for pesticide chemicals.

Under Section 302 of the Emergency Planning and Community Right to Know Act of 1986, propylene oxide is listed as an Extremely Hazardous Substance and has a threshold planning quantity of 10,000 lbs.

Under Section 313 of the Emergency Planning and Community Right to Know Act of 1986, releases of more than 100 lbs/24 hours of propylene oxide into the air, water, and land must be reported annually and entered into the Toxic Release Inventory (TRI).

Facilities having a threshold quantity of 10,000lbs of propylene oxide are subject to the Risk Management Program Rule (RMP), Section 112r of the 1990 Clean Air Act with a toxic endpoint of 0.59 mg/L.

National Overview of 1998 Toxics Release Inventory

In 1998, 122 facilities released 773,937pounds of propylene oxide. Of those releases, 739,974 pounds were air emissions; 1,124 pounds were surface water discharges; 15,303 pounds were released by underground injection; 691 pounds were released to land; and, 16,845 pounds were transferred off-site for disposal. Total emissions for 1998 represented an increase from 1997 emissions, which totaled 609,055 pounds; from 1996 emissions, which totaled 680,747 pounds; a decrease from 1995 emissions, which totaled 909,949 pounds; and a decrease from 1988 (baseline) emissions, which totaled 4,934,754 pounds.

In 1998, 30,772,552 pounds of propylene oxide waste were managed; 1,081,157 pounds were recycled on-site; none was recycled on-site; 13,924,312 pounds were used for energy recovery on-site; 109,647 pounds were used for energy recovery off-site; 14,410,947 pounds were treated on-site; 475,694 pounds were treated off-site; and 770,795 pounds were released on-and off-site.

The 10 states in which the largest amounts of propylene oxide were released in 1998 were: Texas (268,455 pounds); Kentucky (184,237 pounds); California (54,374 pounds); Indiana (48,637 pounds); Louisianna (37,586 pounds); Mississippi (29,591 pounds); Pennsylvania (19,360 pounds); Arkansas (18,502 pounds); Michigan (17,103 pounds); and West Virginia (10,800 pounds).

The 10 facilities releasing the largest amounts of propylene oxide in 1998 were: Carpenter Co., Russellville, KY (179,166 pounds); Huntsman Corp. - C4/O&O Plant, Port Neches, TX (59,450 pounds); Carpenter Co., Pasadena, TX (44,800 pounds); Lyondell Chemical Worldwide Inc., Channelview, TX (36,279 pounds); Lyondell Chemical Worldwide Inc. Bayport Plant, Pasadena, TX (33,736 pounds); Carpenter Co. ,Tupelo Div., Verona, MS (25,823 pounds); A. E. Staley Mfg. Co. Sagamore Ops., Lafayette, IN (25,148 pounds); Rhodia Inc., Vernon, TX (23,900 pounds); Kelco Biopolymers, San Diego, CA (22,574 pounds); and Dow Chemical Co. Louisiana Div., Plaquemine, LA (22,384 pounds).


The NIOSH recommended exposure limits (RELs) are time-weighted average (TWA) concentrations for up to a 10-hour workday during a 40-hour workweek. A short-term exposure limit (STEL) is designated by "ST" preceding the value; unless noted otherwise, the STEL is a 15-minute TWA exposure that should not be exceeded at any time during a workday. A ceiling REL is designated by "C" preceding the value. Any substance that NIOSH considers to be a potential occupational carcinogen is designated by the notation "Ca."

The OSHA permissible exposure limits (PEL) are found in Tables Z-1, Z-2, and Z-3 of the OSHA General Industry Air Contaminants Standard (29 CFR 1910.1000). Unless noted otherwise, PEL are TWA concentrations that must not be exceeded during any 8-hour workshift of a 40-hour workweek. A STEL is designated by "ST" preceding the value and is measured over a 15-minute period unless noted otherwise. OSHA ceiling concentrations (designated by "C" preceding the value) must not be exceeded during any part of the workday; if instantaneous monitoring is not feasible, the ceiling must be assessed as a 15-minute TWA exposure. In addition, there are a number of substances from Table Z-2 (e.g., beryllium, ethylene dibromide, etc.) that have PEL ceiling values that must not be exceeded except for specified excursions. For example, a "5-minute maximum peak in any 2 hours" means that a 5-minute exposure above the ceiling value, but never above the maximum peak, is allowed in any 2 hours during an 8-hour workday.

Information Sources:

  • CAMEO®, U.S. Environmental Protection Agency, National Oceanic and Atmospheric Administration,
  • Chemical Manufacturers Association, 1300 Wilson Blvd., Arlington, VA 22209: (703) 741-5000 or Chemical Referral Library, (800) 262-8200.
  • National Institute of Environmental Health Sciences, Clearinghouse on Environmental Health Effects, 100 Capitola Drive, #108, Durham, NC 27713; (800) 643-4794; fax (919) 361-9408.
  • TOXNET, National Library of Medicine, National Institutes of Health;
  • U.S. Environmental Protection Agency, 401 M St., SW, Washington, DC 20460; Right to Know Hotline (800) 535-0202.
  • U.S. Department of Labor, Occupational Health and Safety Administration, Washington, DC,
  • OSHA PEL: Z-1 Table:
  • OSHA PEL: Z-2 Table:

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