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CHEMINFO Record Number: 347
CCOHS Chemical Name: Propionic acid

Ethanecarboxylic acid
Ethylformic acid
Methylacetic acid
Metacetonic acid
Propanoic acid
Pseudoacetic acid

Chemical Name French: Acide propanoïque
CAS Registry Number: 79-09-4
UN/NA Number(s): 1848
RTECS Number(s): UE5950000
EU EINECS/ELINCS Number: 201-176-3
Chemical Family: Saturated aliphatic carboxylic acid / saturated aliphatic monocarboxylic acid / alkanoic acid / propionic acid
Molecular Formula: C3-H6-O2
Structural Formula: CH3-CH2-C(=O)-OH


Appearance and Odour:
Clear, colourless, oily liquid; pungent, rancid, acrid, irritating, disagreeable odour.(14,15)

Odour Threshold:
0.026-0.17 ppm (geometric mean odour threshold: 0.066) (detection); 0.033 ppm (recognition) (16)

Warning Properties:
GOOD - TLV is more than 10 times the geometric mean odour threshold.

Uses and Occurrences:
Propionic acid is used in the production of its calcium and sodium salts, which are used as antimicrobial agents and mould inhibitors in bread, other baked goods, cheese and cheese products; in animal feed: grain and wood chip preservative; manufacture of fungicides, herbicides, plasticizers, pharmaceuticals, artificial fruit flavourings, perfumes, emulsifying agents, cellulose acetate propionate, used to produce thermoplastics, vinyl propionate, used as a basic monomer for dispersions, and solvents for resins and paints; and additive in electroplating solutions. Propionic acid is a constituent of a variety of foods, including dairy products, and occurs in Swiss cheese at levels as high as 1%.(4,5,14,17)


Clear, colourless, oily liquid with a pungent, rancid, acrid, irritating, disagreeable odour. COMBUSTIBLE LIQUID AND VAPOUR. TOXIC. Harmful following skin contact. CORROSIVE to the eyes and skin. Can cause permanent eye damage, including blindness, or permanent scarring of the skin.


Effects of Short-Term (Acute) Exposure

Inhalation of vapours or mists will likely result in mild to severe irritation of the nose, throat and lungs, depending on airborne concentration. Symptoms would include nasal irritation, sore throat, coughing, hoarseness and, in extreme exposures, difficulty breathing.
Propionic acid is acidic and a related chemical, n-butyric acid, has caused similar effects. No irritant effects were reported among employees exposed to below 0.25 ppm (8-hour average) propionic acid, with excursions up to 2.1 ppm.(1, unconfirmed) Irritation of the nose and throat, and respiratory discomfort were reported among workers exposed to propionic acid, acetic acid, di(2-ethylbutyl)azelate and low levels of ethyl acetate. The exact agent responsible for the reported effects was not determined.(2)

Skin Contact:
Propionic acid can likely cause moderate to severe skin irritation depending upon the concentration of chemical and the duration of contact. Direct contact has caused irritation, redness and pain. Prolonged exposures have caused burns, blistering, and tissue destruction (corrosive effects).
Faint pain after 40 minutes, some redness and swelling and slight tissue death (necrosis) was observed following skin contact with undiluted propionic acid for 1 hour. Healing was complete within three days.(3) Short-term occupational exposures have caused mild to moderate skin burns.(1, unconfirmed) Based on animal studies, the acid can result in serious burns if it is not washed from the skin. Depending on the concentration of the solution and the degree of exposure, corrosive materials can cause permanent scarring.
Based on limited animal information, propionic acid may be absorbed through the skin and cause harmful effects by this route of exposure.

Eye Contact:
Contact with vapour, mist or splashes of dilute solutions can likely cause redness and pain. Direct contact with concentrated solutions can cause corneal burns based on animal information. Depending on the concentration of the solution and the duration of exposure, the damage may be permanent and may include blindness.
Irritation of the eyes was reported among workers who were exposed to propionic acid, acetic acid, di(2-ethylbutyl)azelate and low levels of ethyl acetate. The exact agent responsible for the reported effects was not determined.(2) Mild eye redness has been reported after short-term occupational exposures.(1, unconfirmed)

Propionic acid occurs naturally in Swiss cheese at levels as high as 1%.(4,5) It is used as a food additive because of its antimicrobial effect.(5) It is a corrosive liquid and ingestion of concentrated solutions can cause severe irritation or corrosive injury to the mouth, throat and stomach, based on animal information. Permanent injury and death could result. There is no human information available. Ingestion is not a typical route of occupational exposure.

Effects of Long-Term (Chronic) Exposure

There is no human or animal information available.


There is no human information is available. In one animal study, ingestion of large concentrations of propionic acid caused early evidence of a possible carcinogenic response. No firm conclusions can be drawn based on this limited information.

The International Agency for Research on Cancer (IARC) has not evaluated the carcinogenicity of this chemical.

The American Conference of Governmental Industrial Hygienists (ACGIH) has not assigned a carcinogenicity designation to this chemical.

The US National Toxicology Program (NTP) has not listed this chemical in its report on carcinogens.

Teratogenicity and Embryotoxicity:
There is no human or animal information available.

Reproductive Toxicity:
There is no human or animal information available.

Negative results were obtained in most bacterial test systems and in an in vivo test in hamsters. There is no human information available.

Toxicologically Synergistic Materials:
There is no information available.

Potential for Accumulation:
Propionic acid does not accumulate in the body. It is a normal product of the breakdown of fatty acids and of the side chain of cholesterol in the body. It is rapidly absorbed through the gastrointestinal tract, metabolized, and rapidly used by the body or excreted. Three days after a single oral dose of labelled sodium propionate, 77% of the radioactivity was found in expired air, and 7% in urine and feces.(5)


If symptoms are experienced, remove source of contamination or have victim move to fresh air. Obtain medical advice immediately.

Skin Contact:
Avoid direct contact with this chemical. Wear chemical protective gloves, if necessary. As quickly as possible, flush contaminated area with lukewarm, gently flowing water for 20-30 minutes, by the clock. DO NOT INTERRUPT FLUSHING. If necessary, keep emergency vehicle waiting. Under running water, remove contaminated clothing, shoes, and leather goods (e.g., watchbands, belts). If irritation persists, repeat flushing. Transport victim to an emergency care facility immediately. Completely decontaminate clothing, shoes and leather goods before re-use or discard.

Eye Contact:
Avoid direct contact with this chemical. Immediately flush the contaminated eye(s) with lukewarm, gently flowing water for 20-30 minutes, by the clock, while holding the eyelid(s) open. Neutral saline solution may be used as soon as it is available. DO NOT INTERRUPT FLUSHING. If necessary, keep emergency vehicle waiting. Take care not to rinse contaminated water into the non-affected eye or onto the face. Quickly transport victim to an emergency care facility.

NEVER give anything by mouth if victim is rapidly losing consciousness, or is unconscious or convulsing. Have victim rinse mouth thoroughly with water. DO NOT INDUCE VOMITING. Have victim drink 240 to 300 mL (8 to 10 oz.) of water. If milk is available, it may be administered AFTER the water has been given. If vomiting occurs naturally, have victim rinse mouth and repeat administration of water. Quickly transport victim to an emergency care facility.

First Aid Comments:
Provide general supportive measures (comfort, warmth, rest).
All first aid procedures should be periodically reviewed by a doctor familiar with the material and its conditions of use in the workplace.


Flash Point:
52.2 to 54.4 deg C (126 to 130 deg F) (closed cup) (14)

Lower Flammable (Explosive) Limit (LFL/LEL):
2.9% (15)

Upper Flammable (Explosive) Limit (UFL/UEL):
12.1% (15)

Autoignition (Ignition) Temperature:
Lowest reported value: 466 deg C (870 deg F) (14)

Sensitivity to Mechanical Impact:
Probably not sensitive. Stable material.

Sensitivity to Static Charge:
It has been reported that flow or agitation can cause build-up of electrostatic charge due to propionic acid's low electrical conductivity (100 pS/m at 2 deg C).(17,18)

Combustion and Thermal Decomposition Products:
Acrid smoke and irritating fumes of unburned acid and products of incomplete combustion.(14)

Fire Hazard Summary:
Combustible liquid. Can form explosive mixtures with air at, or above, 52.2 deg C. During a fire irritating/toxic gases may be formed. Reacts with some metals to form flammable hydrogen gas. Vapours from warmed liquid can accumulate in confined spaces, resulting in a explosion and toxicity hazard. Closed containers may rupture violently when exposed to fire or excessive heat for sufficient time.

Extinguishing Media:
Dry chemical powder, carbon dioxide, "alcohol resistant" foam, polymer foam, water spray or fog.(14,19)

Fire Fighting Instructions:
Evacuate area and fight fire from a safe distance or protected location. Approach fire from upwind to avoid hazardous vapours and toxic decomposition products.
Closed containers may rupture violently when exposed to heat of fire. If possible, isolate materials not yet involved in the fire, and move containers from fire area if this can be done without risk, and protect personnel. Otherwise, fire-exposed containers or tanks should be cooled by application of hose streams. Application should begin as soon as possible and should concentrate on any unwetted portions of the container. If this is not possible, use unmanned monitor nozzles and immediately evacuate the area.
If a leak or spill has not ignited, use water spray in large quantities to disperse the vapours, protect personnel attempting to stop a leak and to dilute the spill to a nonflammable mixture. Water spray may be used to flush spills away from ignition sources. Solid streams of water may be ineffective and spread material.
For a massive fire in a large area, use unmanned hose holder or monitor nozzles. If this is not possible, withdraw from fire area and allow fire to burn. Stay away from ends of tanks. Withdraw immediately in case of rising sound from venting safety device or any discolouration of tank due to fire.(14)
Propionic acid and its decomposition products are hazardous to health. Do not enter without wearing specialized protective equipment suitable for the situation. Firefighter's normal protective clothing (Bunker Gear) will not provide adequate protection. Chemical resistant clothing (e.g. chemical splash suit) and positive pressure self-contained breathing apparatus (MSHA/NIOSH approved or equivalent) may be necessary.


NFPA - Health: 3 - Short exposure could cause serious temporary or residual injury.
NFPA - Flammability: 2 - Must be moderately heated or exposed to relatively high ambient temperatures before ignition can occur.
NFPA - Instability: 0 - Normally stable, even under fire conditions, and not reactive with water.


Molecular Weight: 74.08

Conversion Factor:
1 ppm = 3.02 mg/m3; 1 mg/m3 = 0.33 ppm at 25 deg C (calculated)

Physical State: Liquid
Melting Point: -20.8 to -22 deg C (-5.4 to -7.6 deg F) (14,17,20)
Boiling Point: 141.1 deg C (286 deg F) (5,20)
Relative Density (Specific Gravity): 0.992-0.994 (water = 1) (5,17,20)
Solubility in Water: Soluble in all proportions (5,14)
Solubility in Other Liquids: Soluble in all proportions in ethanol, diethyl ether and chloroform.(5)
Coefficient of Oil/Water Distribution (Partition Coefficient): Log P(oct) = 0.25; 0.33 (21)
pH Value: 2.9 (0.1 M solution in water); 2 (about 55% solution in water) (calculated)
Vapour Density: 2.55 (air = 1) (19)
Vapour Pressure: 0.32 to 0.4 kPa (2.4 to 3.0 mm Hg) at 20 deg C (14)
Saturation Vapour Concentration: Approximately 3150 to 4000 ppm (0.32 to 0.4%) at 20 deg C (calculated)
Evaporation Rate: Not available
Critical Temperature: 339 deg C (642.2 deg F) (17)

Other Physical Properties:
ACIDITY: Weak acid; pKa = 4.87 (Ka = 1.338 x 10(-5) at 20 deg C) (17)
VISCOSITY-DYNAMIC: 1.099 mPa.s (1.099 centipoises) at 20 deg C (20)
VISCOSITY-KINEMATIC: 1.106-1.108 mm2/s (1.106-1.108 centistokes) at 20 deg C (calculated)
SURFACE TENSION: 26.7 mN/m (26.7 dynes/cm) at 20 deg C (17)
CRITICAL PRESSURE: 5370 kPa (53 atmospheres) (17)


Normally stable (14)

Hazardous Polymerization:
Does not occur

Incompatibility - Materials to Avoid:

NOTE: Chemical reactions that could result in a hazardous situation (e.g. generation of flammable or toxic chemicals, fire or detonation) are listed here. Many of these reactions can be done safely if specific control measures (e.g. cooling of the reaction) are in place. Although not intended to be complete, an overview of important reactions involving common chemicals is provided to assist in the development of safe work practices.

OXIDIZING AGENTS (e.g. chromium trioxide, nitric acid, peroxides, permanganates) - may react violently or explosively. Increased risk of fire.(14,19,22)
PHOSPHORUS TRICHLORIDE - may form spontaneously flammable phosphine and explode.(23)
REACTIVE METALS (e.g. powdered aluminum or zinc) - may produce flammable hydrogen gas.(18)
POTASSIUM t-BUTOXIDE - may ignite.(23)
REDUCING AGENTS (e.g. hydrides such as lithium aluminum hydride) - reaction may be vigorous or violent.(19)
STRONG BASES (including alkalis, such as sodium hydroxide) - vigorous reaction may occur producing heat and pressure.(19,22)

Hazardous Decomposition Products:
None reported

Conditions to Avoid:
Temperatures above 52 deg C, open flames

Corrosivity to Metals:
Corrosive to steel, grey cast iron, nickel, nickel-chromium-iron alloy and lead.(24) Aluminum is resistant to anhydrous, concentrated acid at room temperature, but not aqueous acid. At higher temperatures, corrosivity varies with concentration. Not corrosive to copper, bronze and brass, up to 141.1 deg C, provided solutions are free of air and oxidizing substances.(17)


LD50 (oral, rat): 4270 mg/kg (6)
LD50 (oral, rat): 2600 mg/kg (7, unconfirmed)

LD50 (dermal, rabbit): 500 mg/kg (6)

Eye Irritation:

Application of in excess of a 5% solution of propionic acid caused severe injury in rabbits (graded 9/10; scored over 5 where 5 is severe injury).(6) Application of 0.99 mg propionic acid produced a severe response in rabbits.(8, unconfirmed)

Skin Irritation:

Application of 0.01 mL of 100% propionic acid produced tissue death (necrosis) in rabbits (graded 6/10).(6)

Effects of Short-Term (Acute) Exposure:

No deaths were observed in rats following inhalation of a saturated vapour concentration (approximately 3800 ppm) of propionic acid for 8 hours.(6)

Damage to the lining of the stomach was observed in dogs following oral administration of 30 mL of 0.1 N propionic acid for 30 minutes.(9) Similar effects were observed in rats, mice and hamsters following feeding of high concentrations (4% propionic acid) in the diet for 7 days in one study (10) and in rats for 21 or 27 days only in a second study (11). In the second study, effects were not observed at 9 or 15 days.(11)

Possible precancerous changes in the stomach (hyperplasia, hyperplastic ulcers and proliferation of basal cells in the stomach) and benign tumours (papillomas) were observed following lifetime feeding of 4% propionic acid in the diet of rats. Only mild evidence of stomach injury (hyperplasia) was observed after feeding rats 0.4% in the diet in the same study.(12, unconfirmed)

Negative results were obtained in one in vivo (micronucleus) test in hamsters.(12)
Negative results have been obtained in the majority of short-term tests conducted. Of 5 studies, only one DNA repair assay using bacteria cells was clearly positive.(12,13)


Selected Bibliography:
(1) Propionic acid. In: Documentation of the threshold limit values and biological exposure indices. 6th edition. American Conference of Governmental Industrial Hygienists, 1991. p. 1294-1295
(2) Gorman, R.W., et al. Health hazard evaluation report, no. HETA-80-186- 1149, TLB Plastics Corporation, Marion, Indiana. National Institute for Occupational Safety and Health, July, 1982
(3) Oettel, H. Effect of organic liquids on the skin. Archiv fuer Experimentelle Pathologie. Vol. 83 (1936). p. 641-696. (English translation: NIOSHTIC Control Number: 00071872)
(4) Furia, T.E., editor. CRC handbook of food additives. 2nd edition. Volume 1. CRC Press, 1972. p. 137-141
(5) Katz, G.V., et al. Aliphatic carboxylic acids. In: Patty's industrial hygiene and toxicology. 4th edition. Edited by G.D. Clayton et al. Volume II. Toxicology. Part E. John Wiley and Sons, 1994. p. 3525, 3528, 3536-3538
(6) Smyth, H.F., et al. Range-finding toxicity data: list VI. American Industrial Hygiene Association Journal. Vol. 23, no. 1 (1962). p. 95-107
(7) Toxicological evaluation of some food additives including anticaking agents, antimicrobials, antioxidants, emulsifiers and thickening agents. WHO Food Additives Series, 1974, No. 5. World Health Organization, 1974. p. 110- 118
(8) RTECS record for propionic acid. Last updated: 9603
(9) Davenport, H.W. Gastric mucosal injury by fatty and acetylsalicylic acids. Gastroenterology. Vol. 46, no. 3 (March, 1964). p. 245-253
(10) Harrison, P.T., et al. Early changes in the forestomach of rats, mice and hamsters exposed to dietary propionic and butyric acid. Food and Chemical Toxicology. Vol. 29, no. 6 (1991). p. 367-371
(11) Rodrigues, C. et al. Short-term effects of various phenols and acids on the Fischer 344 male rat forestomach epithelium. Toxicology. Vol. 38, no. 1 (1986). p. 103-117
(12) Basler, A. Screening of the food additive propionic acid for genotoxic properties. Food and Chemical Toxicology. Vol. 25, no. 4 (1987). p. 287-290
(13) Sipi, P.H., et al. Sister-chromatid exchanges induced by vinyl esters and respective carboxylic acids in cultured human lymphocytes. Mutation Research. Vol. 279, no. 2 (May, 1992). p. 75-82
(14) Emergency action guide for propionic acid. Association of American Railroads, January, 1988
(15) Fire protection guide to hazardous materials. 13th ed. Edited by A.B. Spencer, et al. National Fire Protection Association, 2002. NFPA 325; NFPA 49
(16) Odor thresholds for chemicals with established occupational health standards. American Industrial Hygiene Association, 1989. p. 28, 73-74
(17) Samel, U-R., et al. Propionic acid and derivatives. In: Ullmann's encyclopedia of industrial chemistry. 5th completely revised edition. Volume A 22. VCH Verlagsgesellschaft, 1993. p. 223-238
(18) Chemical safety sheets: working safely with hazardous chemicals. Kluwer Academic Publishers, 1991. p. 755
(19) The Sigma-Aldrich library of chemical safety data. Edition II. Volume 2. Sigma-Aldrich Corporation, 1988. p. 2957C
(20) Bagby, M.O. Carboxylic acids: survey. In: Kirk-Othmer encyclopedia of chemical technology. 4th edition. Volume 5. John Wiley and Sons, 1993. p. 147-168
(21) Leo, A., et al. Partition coefficients and their uses. Chemical Reviews. Vol. 71, no. 6 (December, 1971). p. 560
(22) NIOSH pocket guide to chemical hazards. National Institute for Occupational Safety and Health, June 1994. p. 2-3; 266-267
(23) Urben, P.G., ed. Bretherick's handbook of reactive chemical hazards. 5th edition. Volume 1. Butterworth-Heinemann Ltd., 1995. p. 567, 1350
(24) Corrosion data survey: metals section. 6th edition. National Association of Corrosion Engineers, 1985. p. 104-8 to 105-8
(25) Abramova, Yu V. Separate determination of C1 to C9 monocarboxylic acids in air by paper chromatography. Hygiene and Sanitation. Vol. 33, no. 6 (1968). p. 360-362
(26) Forsberg, K., et al. Quick selection guide to chemical protective clothing. 4th ed. Van Nostrand Reinhold, 2002
(27) European Economic Community. Commission Directive 93/72/EEC. September 1, 1993
(28) Industrial Bio-Test Labs Inc. Primary skin irritation tests with eighteen materials in albino rabbits with cover letter dated 061589. Date produced: July 28, 1972. Hoechst Celanese Corp. EPA/OTS 86-890001277. NTIS/OTS0520783.
(29) Sekizawa, J., et al. A simple method for screening assessment of skin and eye irritation. Journal of Toxicological Sciences. Vol. 19, no. 1 (1994). p. 25-35

Information on chemicals reviewed in the CHEMINFO database is drawn from a number of publicly available sources. A list of general references used to compile CHEMINFO records is available in the database Help.

Review/Preparation Date: 1997-04-30

Revision Indicators:
US transport 1998-03-01
Resistance of materials 1998-04-01
Bibliography 1998-04-01
Emergency overview 2000-08-01
Acute exposure (ingestion) 2000-08-01
First aid (ingestion) 2000-08-01
TDG 2002-05-29
Bibliography 2003-04-16
PEL-TWA final 2003-12-04
Resistance of materials for PPE 2004-04-05
Bibliography 2004-04-05
Bibliography 2006-03-30

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