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CHEMINFO Record Number: 738
CCOHS Chemical Name: Potassium hydroxide solid

Caustic potash
Potassium hydrate
Hydroxyde de potassium (solide)
Potassium hydroxide (non-specific name)

Chemical Name French: Hydroxyde de potassium (solide)
Chemical Name Spanish: Hidróxido de potasio
Hidróxido potásico
Potasa caústica
CAS Registry Number: 1310-58-3
Other CAS Registry Number(s): 29857-72-5 71769-53-4
UN/NA Number(s): 1813
RTECS Number(s): TT2100000
EU EINECS/ELINCS Number: 215-181-3
Chemical Family: Potassium and compounds / inorganic potassium compound / alkali metal hydroxide
Molecular Formula: H-K-O
Structural Formula: KOH


Appearance and Odour:
White or slightly yellow, odourless, non-volatile pellets, flakes, lumps or sticks. Deliquescent (absorbs moisture from the air and forms wet solutions).(10,17,18)

Odour Threshold:

Warning Properties:
POOR - odourless

Potassium hydroxide is a solid, commonly sold in the form of pellets, flakes, lumps or sticks. It is commonly 83-90% pure, with 2-3% potassium carbonate and the remainder (8-15%) predominantly water, in the form of hydrates (mono-, di- and tetrahydrates). Very high purity grades (99%+) are available. Potassium hydroxide is also available in solution. This record reviews the information for the solid form. CHEMINFO record 9 reviews information for solutions.

Uses and Occurrences:
Chemical intermediate for the production of inorganic potassium chemicals. Used in the manufacture of soaps, printing inks, paint and varnish removers, dyestuffs, liquid fertilizers and herbicides. Used in electroplating, photoengraving and lithography; veterinary medicine; petroleum refining; scrubbing and cleaning operations; and in analytical chemistry and organic synthesis. Used as an electrolyte in alkaline storage batteries and some fuel cells; a mordant for wood; for mercerizing cotton; an absorbent for carbon dioxide and hydrogen sulfide; and as a food additive.(15,16)


White or slightly yellow, odourless, non-volatile pellets, flakes, lumps or sticks. Deliquescent. Will not burn. Highly reactive. Can react violently with water and many commonly encountered materials, generating enough heat to ignite nearby combustible materials. Contact with many organic and inorganic chemicals may cause fire or explosion. Reaction with metals releases flammable hydrogen gas. EXTREMELY CORROSIVE. Can cause blindness, permanent scarring and death. Aerosols can cause lung injury--effects may be delayed.


Effects of Short-Term (Acute) Exposure

Potassium hydroxide does not readily form a vapour and inhalation exposure is only likely to occur to aerosols since the solid is deliquescent and not likely to form a dust. Potassium hydroxide would probably cause severe irritation of the respiratory tract based on human information for the closely related alkali hydroxide, sodium hydroxide, and the corrosive nature of potassium hydroxide. In severe cases, pulmonary edema (severe, life- threatening lung injury) could result.

Skin Contact:
There is no specific information available for solid potassium hydroxide, but it is probably a severe irritant or corrosive. Potassium hydroxide solutions are extremely corrosive and are capable of causing severe burns with deep ulceration, penetrating to deeper layers of skin causing permanent scarring and possibly death. The severity of injury depends on the concentration of the solution and the duration of exposure. The burns may not be immediately painful; onset of pain may be minutes to hours.

Eye Contact:
There is no specific information available for solid potassium hydroxide, but it is probably a severe irritant or corrosive. Potassium hydroxide solutions are extremely corrosive and can penetrate deeply, causing irritation or severe burns depending on the concentration and duration of exposure. In severe cases, ulceration and permanent blindness may occur.

There are no reported cases of occupational ingestion of potassium hydroxide. Ingestion is not a typical route of occupational exposure.
A review of 31 non-occupational cases of ingestion of strong alkalies showed that 3 people had ingested potassium hydroxide and 28 sodium hydroxide. Symptoms included pain, excessive salivation, vomiting and retching. Observed effects included corrosive burns of the esophagus, stomach and duodenum. Perforation of the esophagus or stomach occurred in 5 cases and there were 4 deaths. Seventeen survivors developed strictures of the esophagus and/or stomach. The authors observed that the degree and extent of burns with respect to type of alkali was not noticeably different.(1)

Effects of Long-Term (Chronic) Exposure

There have been no documented effects due to long-term exposure to potassium hydroxide. Repeated skin contact may result in drying, cracking and inflammation.


Potassium and sodium hydroxide have been implicated as a cause of cancer of the esophagus in individuals who have ingested it. The cancer may develop 12 to 42 years after the ingestion incident. Similar cancers have been observed at the sites of severe thermal burns. These cancers are due to tissue destruction and scar formation rather than the action of the hydroxide itself.(2,3,4,5,6)

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:
No human or animal information available.

Reproductive Toxicity:
No human or animal information available.

There is no in vivo information available. In vitro information suggests that potassium hydroxide is not mutagenic.

Toxicologically Synergistic Materials:
No information available.

Potential for Accumulation:
Does not accumulate


Remove source of contamination or move victim to fresh air. If breathing is difficult, oxygen may be beneficial if administered by trained personnel, preferably on a doctor's advice. DO NOT allow victim to move about unnecessarily. Symptoms of pulmonary edema can be delayed up to 48 hours after exposure. Immediately transport victim to an emergency care facility.

Skin Contact:
Avoid direct contact with this chemical. Wear chemical protective clothing, if necessary. Quickly and gently blot or brush away excess chemical. As quickly as possible, remove contaminated clothing, shoes and leather goods (e.g. watchbands, belts). Flush contaminated area with lukewarm, gently flowing water for at least 60 minutes, by the clock. DO NOT INTERRUPT FLUSHING. If necessary, keep emergency vehicle waiting. Transport victim to an emergency care facility immediately. Discard contaminated clothing, shoes and leather goods.

Eye Contact:
Avoid direct contact. Wear chemical protective gloves, if necessary. Quickly and gently blot or brush away excess chemical. Immediately flush the contaminated eye(s) with lukewarm, gently flowing water for at least 60 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 unaffected eye or onto the face. Quickly transport victim to an emergency care facility.

NEVER give anything by mouth if victim is rapidly losing consciousness, 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 to dilute material in stomach. If milk is available, it may be administered AFTER the water has been given. If vomiting occurs naturally, repeat administration of water. Quickly transport victim to an emergency care facility.

First Aid Comments:
Provide general supportive measures (comfort, warmth, rest). Consult a doctor and/or the nearest Poison Control Centre for all exposures except minor instances of inhalation contact.
Some recommendations in the above sections may be considered medical acts in some jurisdictions. These recommendations should be reviewed with a doctor and appropriate delegation of authority obtained, as required.
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:
Non-combustible (does not burn)

Lower Flammable (Explosive) Limit (LFL/LEL):
Not applicable

Upper Flammable (Explosive) Limit (UFL/UEL):
Not applicable

Autoignition (Ignition) Temperature:
Not applicable

Sensitivity to Mechanical Impact:
Not sensitive. Stable material.

Sensitivity to Static Charge:
Not applicable. Not combustible.

Combustion and Thermal Decomposition Products:
Toxic potassium oxide fumes.

Fire Hazard Summary:
Potassium hydroxide will not burn or support combustion. However, reaction of potassium hydroxide with a number of commonly encountered materials (see Chemical Reactivity) can generate sufficient heat to ignite nearby combustible materials. Potassium hydroxide can react with metals, such as aluminum, tin and zinc, to form flammable and explosive hydrogen gas.

Extinguishing Media:
Use an extinguisher appropriate for the surrounding fire. If water is used, care should be taken, since it can generate heat and cause spattering if applied directly to potassium hydroxide. Also, use care if carbon dioxide is used, since it reacts with potassium hydroxide with the generation of heat.

Fire Fighting Instructions:
Evacuate area and fight fire from a safe distance or a protected location. Approach fire from upwind. If possible, isolate materials not involved in the fire and protect personnel. Move containers from fire area if it can be done without risk.
Water can be used with extreme caution to extinguish a fire in an area where potassium hydroxide is stored. The water must not come into contact with the potassium hydroxide. Water can be used in flooding quantities as a spray or fog to keep fire-exposed containers cool and absorb heat.
At high temperatures, fuming may occur, giving off a strong, corrosive gas. 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: 0 - Will not burn under typical fire conditions.
NFPA - Instability: 1 - Normally stable, but can become unstable at elevated temperatures and pressures, or may react vigorously, but non-violently with water.


Molecular Weight: 56.11

Conversion Factor:
Not applicable

Physical State: Solid
Melting Point: 360 deg C (680 deg F) (varies with water content) (17,18); 380 deg C (716 deg F) (anhydrous) (15)
Boiling Point: 1320-1324 deg C (2408-2415 deg F) at 101.33 kPa (17)
Relative Density (Specific Gravity): 2.044 at 15 deg C (water=1) (17,18)
Solubility in Water: Very soluble (111 g/100 mL at 25 deg C) (15,16)
Solubility in Other Liquids: Soluble in ethanol and glycerol; insoluble in diethyl ether and ammonia.(16,17)
Coefficient of Oil/Water Distribution (Partition Coefficient): Not available
pH Value: 13.5 (0.1M (0.56%) solution) (15); 14 (1M (5.6%) solution at 25 deg C)
Vapour Density: Not applicable
Vapour Pressure: Negligible at room temperature
Saturation Vapour Concentration: Not applicable
Evaporation Rate: Not applicable
Critical Temperature: Not applicable


Normally stable. Potassium hydroxide rapidly absorbs carbon dioxide from the air (forming potassium carbonate).(15)

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.

Potassium hydroxide reacts vigorously, violently or explosively with many organic and inorganic chemicals, such as strong acids, acid chlorides, acid anhydrides, nitroaromatic, nitroparaffin and organohalogen compounds and organic peroxides.
Reacts violently with water generating significant heat and dangerously spattering corrosive potassium hydroxide.
Violently polymerizes acetaldehyde, acrolein or acrylonitrile.
Produces flammable and explosive hydrogen gas if it reacts with sodium tetrahydroborate or metals, such as aluminum, tin, or zinc.
Produces spontaneously flammable phosphine gas if it reacts with phosphorus.
Can form spontaneously flammable chemicals upon contact with 1,2- dichloroethylene, trichloroethylene or tetrachloroethane.
Can react explosively with chlorine dioxide, maleic anhydride, nitrogen trichloride, n-nitrosomethylurea and tetrahydrofuran.
Can produce carbon monoxide upon contact with solutions of sugars, such as fructose, lactose and maltose.
References 19, 21 and 22 provide more complete lists of chemicals that may react hazardously with potassium hydroxide.

Hazardous Decomposition Products:
Potassium carbonate

Conditions to Avoid:
Water, moisture

Corrosivity to Metals:
Corrosive to aluminum, lead, tin, zinc, copper, brass and bronze. Corrosive to steel at elevated temperatures (above 40 deg C). Not corrosive to nickel.(23)

Stability and Reactivity Comments:
Will attack wool and leather. Practically non-corrosive to rubber.(20)


LD50 (oral, rat): 365 mg/kg (7)
LD50 (oral, male rat): 273 mg/kg (8)

Eye Irritation:

Application of 0.1 mL of 5.0% potassium hydroxide solution for 5 minutes, before washing the eye with distilled water for 2 minutes, resulted in extreme irritation and corrosion in rabbits. Application of 0.1 mL of a 1% solution for 5 minutes, or 24 hours before washing the eye resulted in irritation. A 0.1% solution applied for 24 hours before washing the eye caused no irritation.(7)

Skin Irritation:

A 10% solution was corrosive to rabbits and guinea pigs when applied to intact or broken skin for 4 hours. Severe destruction or irreversible alterations in the tissue at the site of contact were produced in all animals tested.(9) Application of 0.1 mL of a 5% solution to intact or broken skin of rabbits for 24 hours resulted in mild irritation to intact skin and extreme irritation of broken skin.(7)

Effects of Short-Term (Acute) Exposure:

Exposure to very low doses, even for a short period of time, has produced extensive damage to the esophagus, stomach and intestine extending into surrounding tissues, as well as hyperexcitability followed by apathy and weakness. In some cases, death has resulted from haemorrhage, adhesions or perforation. Following esophageal damage, strictures have frequently developed in surviving animals.(2,10,11)

Skin Sensitization:
Potassium hydroxide did not cause skin sensitization in guinea pigs in one study.(7)

In a poorly reported study designed to assess the carcinogenic effect of prolonged and repeated applications of potassium hydroxide, 3-6% solutions were applied to the skin of mice for 25-46 weeks at a frequency that would avoid deep lesions but not allow healing to occur. Tumours developed in 15% of the treated areas. However, the authors noted that considerable difficulty was encountered in judging whether the tumours were malignant or benign.(12) No conclusions can be drawn from this study.


Selected Bibliography:
(1) Zargar, S.A., et al. Ingestion of strong corrosive alkalis: spectrum of injury to upper gastrointestinal tract and natural history. The American Journal of Gastroenterology. Vol. 87, no. 3 (March, 1992). p. 337- 341
(2) Ashcroft, K.W., et al. The effect of dilute corrosives on the esophagus. Pediatrics. Vol. 53, no. 2 (February, 1974). p. 226-232
(3) Benedict, E. Carcinoma of the esophagus developing in benign stricture. New England Journal of Medicine. Vol. 224 (1941). p. 408-412
(4) Bigelow, N.H. Carcinoma of the esophagus developing at the site of lye stricture. Cancer. Vol. 6 (1953). p. 1159-1164
(5) Gerami, S., et al. Carcinoma of the esophagus engrafted on lye stricture. Chest. Vol. 59, no. 2 (1971) p. 226-227
(6) Parkinson, A.T., et al. Verrucous squamous cell carcinoma of the esophagus following lye stricture. Chest. Vol. 57, no. 5 (1970). p. 489- 492
(7) Johnson, G.T., et al. Acute toxicity of cesium and rubidium compounds. Toxicology and Applied Pharmacology. Vol. 32 (1975). p. 239-245
(8) Bruce, R.D. A confirmatory study of the up-and-down method for acute oral toxicity testing. Fundamental and Applied Toxicology. Vol. 8 (1987). p. 97-100
(9) Nixon, G.A., et al. Interspecies comparisons of skin irritancy. Toxicology and Applied Pharmacology. Vol. 31 (1975). p. 481-490
(10) NIOSH pocket guide to chemical hazards. National Institute for Occupational of Safety and Health, June, 1994. p. 262-263, 284-285
(11) Bosher, Jr., L.H., et al. The pathology of experimentally produced lye burns and strictures of the esophagus. Journal of Thoracic and Cardiovascular Surgery. Vol. 21 (1951). p. 483-489
(12) Narat, J.K. Experimental production of malignant growths by simple chemicals. Journal of Cancer Research. Vol. 9 (1925). p. 135-147
(13) Morita, T., et al. Effects of pH in the in vitro chromosomal aberration test. Mutation Research. Vol. 225 (1989). p. 55-60
(14) Demerec, M., et al. A survey of chemicals for mutagenic action on E. Coli. The American Naturalist. Vol. 85, no. 821 (March-April, 1951). p. 119-136
(15) The Merck index: an encyclopedia of chemicals, drugs, and biologicals. 11th edition. Merck & Co., Inc., 1989. p. 1215
(16) HSDB record for potassium hydroxide. Last revision date: 95-01-24.
(17) Potassium hydroxide. In: Documentation of the threshold limit values and biological exposure indices. 6th edition. American Conference of Governmental Industrial Hygienists, 1994. p. 1284-1285
(18) Pierce, J.O. Alkaline materials. In: Patty's Industrial Hygiene and Toxicology. 4th Edition. Edited by G.D. Clayton, et al. Toxicology. Volume II, Part A. John Wiley & Sons, Inc, 1993. p. 755, 766-768, 779-782
(19) Fire protection guide to hazardous materials. 13th ed. Edited by A.B. Spencer, et al. National Fire Protection Association, 2002. NFPA 49; NFPA 491
(20) Emergency action guide for potassium hydroxide. Association of American Railroads, January, 1988
(21) Bretherick, L. Bretherick's handbook of reactive chemical hazards. 4th edition. Butterworths, 1990. p. 1143-1145
(22) The Sigma-Aldrich library of chemical safety data. Edition II. Volume 2. Sigma-Aldrich Corporation, 1988. p. 2904D
(23) Corrosion data survey: metals section. 6th edition. National Association of Corrosion Engineers, 1985. p. 102-103
(24) Forsberg, K., et al. Quick selection guide to chemical protective clothing. 4th ed. Van Nostrand Reinhold, 2002
(25) European Communities. Commission Directive 98/98/EC. December 15, 1998
(26) Occupational Safety and Health Administration (OSHA). Metal and Metalloid Particulates in Workplace Atmospheres (Atomic Absorption). In: OSHA Analytical Methods Manual. Revision Date: Oct. 31, 2001. Available at: <>
(27) National Institute for Occupational Safety and Health (NIOSH). Alkaline Dusts. In: NIOSH Manual of Analytical Methods (NMAM(R)). 4th ed. Edited by M.E. Cassinelli, et al. DHHS (NIOSH) Publication 94-113. (Aug. 1994). Available at: <>

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: 1996-01-30

Revision Indicators:
Sampling 1996-06-01
Respiratory guidelines 1996-06-01
US transport 1998-03-01
Resistance of materials 1998-05-01
EU Class 2000-04-01
EU Risk 2000-04-01
EU Safety 2000-04-01
EU Comments 2000-04-01
Bibliography 2000-04-01
TDG 2002-05-29
Bibliography 2003-04-15
Resistance of materials for PPE 2004-04-02
Bibliography 2004-04-02
Sampling/analysis 2005-02-28
Bibliography 2005-02-28

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