Hazardous substance assessment - Potassium hydroxide

Identification

Chemical name:

Potassium hydroxide

CAS #:

1310-58-3

Chemical composition:

KOH

Synonyms:

Potash lye; Caustic potash; Potash.

UN #:

1813 (Solid), 1814 (Solution)

Pictogram(s):

Figure 1 - Text description

The symbol within the pictogram shows a container dripping liquid onto a piece of metal and another container dripping liquid onto a hand. This symbol indicates that hazardous products with this pictogram can:

• damage or destroy metal
• cause irreversible damage to the skin (for example, burns, blisters, scarring)
• produce tissue damage in the eye or vision loss that is irreversible or not fully reversible within 21 days

Figure 2 - Text description

The symbol within the pictogram is a human skull with 2 crossed bones behind it. The symbol indicates that hazardous products with this pictogram can cause death or poisoning.

WHMIS classification

Health hazards:

Acute Toxicity (Oral) - Category 3

Skin Corrosion - Category 1

Serious Eye Damage - Category 1

Physical hazards:

Potassium hydroxide does not meet the criteria for classification.

Health hazards

Acute Toxicity (Oral):

Category 3

Median lethal dose (LD₅₀): 205 mg/kg (rat)^Footnote 1.

The available data meet the classification criteria for Acute Toxicity (Oral) - Category 3 [HPR 8.1.1(1)].

Acute Toxicity (Dermal):

Does not meet criteria

LD₅₀: ≤ 2,000 mg/kg and >1,260 mg/kg (rabbit) ^Footnote 1.

In 1 non-guideline study, rabbits (1 per dose) were administered a 45% aqueous solution of potassium hydroxide in doses ranging from 1,000 mg to 3,160 mg/kg ^Footnote 1. No mortality occurred at 1,260 mg/kg, but 1/1 animal died at 2,000 mg/kg and above. The LD₅₀ value was reported to be ≤ 2,000 mg/kg and >1,260 mg/kg, which is equivalent to an acute toxicity point estimate of 1,100 mg/kg as per HPR 8.1.7. Because this study involves the use of a single animal per dose, it is insufficient for classification.

The available data do not meet the classification criteria for Acute Toxicity (Dermal).

Acute Toxicity (Inhalation - Gases):

Not applicable

Potassium hydroxide is not a gas. The classification criteria for Acute Toxicity (Inhalation - Gases) do not apply to this substance.

Acute Toxicity (Inhalation - Vapours):

No data available

Acute Toxicity (Inhalation - Dusts and Mists):

No data available

Skin Corrosion / Irritation:

Category 1

In a purposely generated animal study, 0.5 mL of 5% and 10% aqueous solutions of potassium hydroxide produced a corrosive response that exceeded the Draize grading scale (0-8) after 4 hours of application ^Footnote 2 following gradings at 24, 48 and 72 hours post-exposure. These results meet the classification criteria for Skin Corrosion - Category 1 [HPR 8.2.2(2)]. Several other studies also reported that 0.5 mL of 2%, 5%, and 10% aqueous solutions of potassium hydroxide produced necrosis after 4 hours of application that extended beyond the application sites [^Footnote 3,^Footnote 4,^Footnote 5,^Footnote 6,^Footnote 7 ]. With the 10% solution, edema could not be evaluated due to the severity of the reactions after 4 hours of application. In another study, a 1% solution of potassium hydroxide was not corrosive in animals ^Footnote 5.

Due to the absence of animal data looking at shorter exposure durations, subcategorization is not possible.

The available data meet the classification criteria for Skin Corrosion - Category 1 [HPR 8.2.2(2)].

Serious Eye Damage / Eye Irritation:

Category 1

No human data are available. In an Organisation for Economic Co-operation and Development Test Guideline 405-compliant animal study, 0.1 mL of a 5% solution was extremely irritating and corrosive to albino rabbit eyes after a 5-minute exposure ^Footnote 8. The results meet the classification criteria for Serious Eye Damage – Category 1 [HPR 8.3.2(1)]. The same study reported that a 1% solution was irritating after 5-minute and 24-hour exposure periods, a 0.5% solution was slightly irritating after 24 hours of exposure, and a 0.1% solution was not irritating at all. No scores were reported. The available data meet the classification criteria for Category 1 for a ≥5% potassium hydroxide solution [HPR 8.3.2(1)].

The available data meet the classification criteria for Serious Eye Damage - Category 1 [HPR 8.3.2(1)].

Respiratory Sensitization:

No data available

Skin Sensitization:

Does not meet criteria

In the only available study, which did not follow any guidelines, an intra-cutaneous induction of 0.1 % potassium hydroxide (85% pure) in guinea pigs, 3 times weekly for a total of 9 treatments, did not result in skin sensitization when challenged with the same concentration 2 weeks after the final induction (0/5 animals responded) ^Footnote 6.

The available data do not meet the classification criteria for Skin Sensitization.

Germ Cell Mutagenicity:

Does not meet criteria

In vivo: No studies are available.

In vitro: Potassium hydroxide tested negative in an Ames test, with and without metabolic activation (based on study summary ^Footnote 9). Potassium hydroxide tested positive in a chromosome aberration assay in Chinese hamster ovary cells, with and without metabolic activation; however, the positive response was attributed to the non-physiological pH (10.4) of the potassium hydroxide solution tested ^Footnote 10.

The available data do not meet the classification criteria for Germ Cell Mutagenicity.

Carcinogenicity:

No data available

Potassium hydroxide has not been reviewed by the International Agency for Research on Cancer (IARC), the National Toxicology Program (NTP), or the American Conference of Governmental Industrial Hygienists (ACGIH).

No carcinogenicity studies were available.

Reproductive Toxicity:

No data available

Specific Target Organ Toxicity - Single Exposure:

Does not meet criteria

Oral Route of Exposure: The acute ingestion of potassium hydroxide has been shown to cause severe corrosive burns to the esophagus, stomach and duodenum in both humans and animals ^Footnote 6,^Footnote 11. In severe cases, deaths have been reported. As the effects can be lethal, and given that it has been classified in the more severe hazard class for this route (Acute Toxicity (Oral)), potassium hydroxide does not meet classification criteria.

Dermal Route of Exposure: No data available

Inhalation Route of Exposure: No data available

The available data do not meet the classification criteria for Specific Target Organ Toxicity - Single Exposure.

Specific Target Organ Toxicity - Repeated Exposure:

No data available for oral, dermal or inhalation routes of exposure

Aspiration Hazard:

No data available

No human data are available for potassium hydroxide. This substance is not a liquid hydrocarbon.

Biohazardous Infectious Materials:

Not applicable

Potassium hydroxide is not a microorganism, protein, or nucleic acid.

Physical hazards

Explosives:

Not evaluated*

* Explosives are excluded from the HPA and its regulations. Explosives are regulated under the Explosives Act. For more information, visit Natural Resources Canada.

Flammable Gases:

Not applicable

Potassium hydroxide is not a gas. The classification criteria for Flammable Gases do not apply to this substance.

(Flammable) Aerosols:

Not evaluated

Classification of a hazardous product in the Flammable Aerosols or Aerosols hazard class is product dependent.

Oxidizing Gases:

Not applicable

Potassium hydroxide is not a gas. The classification criteria for Oxidizing Gases do not apply to this substance.

Gases Under Pressure:

Not applicable

Potassium hydroxide is not a gas. The classification criteria for Gases Under Pressure do not apply to this substance.

Flammable Liquids:

Not applicable

Potassium hydroxide is not a liquid. It is hygroscopic and dissolves readily in water^Footnote 12,^Footnote 13. Potassium and hydroxide ions are quite stable in solution and, thus, potassium hydroxide is not flammable when dissolved (based on study summary ^Footnote 9).

The classification criteria for Flammable Liquids do not apply to this substance.

Flammable Solids:

Does not meet criteria

The inorganic element in potassium hydroxide is in its highest oxidation state, making it unable to react with oxygen, and the substance is considered non-flammable (based on study summary ^Footnote 9).

The available data do not meet the classification criteria for Flammable Solids.

Self-Reactive Substances and Mixtures:

Does not meet criteria

Potassium hydroxide is a non-flammable substance and is not auto-flammable up to a temperature of 400 °C (based on study summary ^Footnote 9). Self-Reactive Substances and Mixtures must have a self-accelerating decomposition temperature (SADT) of ≤75 °C to meet the minimum classification in this hazard class.

The available data do not meet the classification criteria for Self-reactive Substances and Mixtures.

Pyrophoric Liquids:

Not applicable

Potassium hydroxide is not a liquid. The classification criteria for Pyrophoric Liquids do not apply to this substance.

Pyrophoric Solids:

Does not meet criteria

The inorganic element in potassium hydroxide is in its highest oxidation state, making it unable to react with oxygen (based on study summary ^Footnote 9).

The available data do not meet the classification criteria for Pyrophoric Solids.

Self-Heating Substances and Mixtures:

Does not meet criteria

Potassium hydroxide did not demonstrate auto-flammability at temperatures up to 400°C (based on study summary ^Footnote 9), which is well above the maximum spontaneous ignition temperature of 140°C for classification.

The available data do not meet the classification criteria for Self-heating Substances and Mixtures.

Substances and Mixtures which, in Contact with Water, Emit Flammable Gases:

Does not meet criteria

Potassium hydroxide is a strong alkali that dissociates completely in water into the potassium ion (K+) and hydroxyl ion (OH-). The dissolution/dissociation in water is strongly exothermic, so a vigorous reaction occurs when potassium hydroxide is added to water (based on study summary ^Footnote 9). However, no testing has been done in accordance with test N.5 of sub-section 33.5.4 of Part III of the Manual of Tests and Criteria to determine a classification.

The available data do not meet the classification criteria for Substances and Mixtures which, in Contact with Water, Emit Flammable Gases.

Oxidizing Liquids:

Not applicable

Potassium hydroxide is not a liquid. The classification criteria for Oxidizing Liquids do not apply to this substance.

Oxidizing Solids:

No data available

While potassium hydroxide does not meet the exclusion of paragraph 7.14.1(1)(c) of the HPR, no data from a test referred to in subsection 7.14.1(2) of the HPR are available for evaluation.

Organic Peroxides:

Not applicable

Potassium hydroxide is an inorganic compound and is not a peroxide. The classification criteria for Organic Peroxides do not apply to this substance.

Corrosive to Metals:

No data available

Potassium hydroxide, when wet, attacks metals such as aluminium, tin, lead and zinc to produce flammable hydrogen gas (based on study summary ^Footnote 9). Two publications have reported corrosion rate values for potassium hydroxide on aluminum, > 50 mil/year (equivalent to >1.27 mm/year at 15°C, 5-90% KOH in aqueous solution) ^Footnote 14 and 0.8 mg.cm-2.min-1 (equivalent to 7.8 mm/year at 50°C, 22.5% KOH in aqueous solution) ^Footnote 15.

The temperatures used in the above studies are not those required by the test method prescribed in section 7.16.1 of the HPR (55°C). As such, no data are available that are suitable to determine whether potassium hydroxide meets the classification criteria for Corrosive to Metals.

Combustible Dusts:

No data available

No data are available to determine whether potassium hydroxide meets the classification criteria for Combustible Dusts.

Simple Asphyxiants:

Not applicable

Potassium hydroxide is not a gas. The classification criteria for Simple Asphyxiants do not apply to this substance.

Pyrophoric Gases:

Not applicable

Potassium hydroxide is not a gas. The classification criteria for Pyrophoric Gases do not apply to this substance.

Chemicals Under Pressure:

Not evaluated

Classification of a hazardous product in the Chemicals Under Pressure hazard class is product dependent.

Regulatory and other information

Regulatory information:

Hazardous substance assessments are prepared by Health Canada as educational and information resources. Under the HPA, suppliers of hazardous products must, upon the sale or importation of a hazardous product, provide safety data sheet and label that meet the requirements set out in the HPR.

Other information:

The information and classifications contained in these hazardous substance assessments are based on publicly available sources, such as peer-reviewed literature or reports by international bodies. New information, including proprietary information, could have an impact on the classification of substances or hazardous products containing them. It is the responsibility of the supplier to ensure the accuracy, sufficiency, and reliability of their hazardous product classifications.

Last updated:

2022

Prepared by:

Workplace Hazardous Materials Bureau, Health Canada