Mists from Strong Inorganic Acids Profile


IARC Monograph Vol. 54, 1992 (Group 1)
IARC Monograph Vol. 100F, 2012 (Group 1)

Mists from Strong Inorganic Acids Profile

General Information

Strong inorganic acid mists (which often include sulfuric acid) are liquid aerosols formed when acid vapour is condensed or liquid is atomized.[1] The formulation of the mist depends on factors such as industrial process, solution strength, and atmospheric conditions (i.e. temperature).[1]

Sulfuric acid mists can form in the atmosphere when naturally-occurring sulphur dioxide combines with sunlight and chemicals released by industrial processes.[2] However, exposures to environmental acid mists are not included in this profile as they have not been reviewed specifically with respect to carcinogenicity; only the higher exposure levels associated with workplaces are known to be carcinogenic.[2]

Occupational exposure to mists from strong inorganic acids is classified by the International Agency for Research on Cancer (IARC) as Group 1, carcinogenic to humans, on the basis of sufficient evidence of carcinogenicity in humans. Epidemiological studies reviewed by IARC show strong evidence that mists from strong organic acids cause laryngeal cancer.[2] A positive association between exposure to these mists and lung cancer has also been observed.[2]

Additional adverse health effects from breathing sulfuric acid mists in particular include tooth erosion and respiratory tract irritation.[3]

Regulations and Guidelines

Occupational exposure limits (OEL) [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]

Canadian Jurisdictions Sulfuric acid (mg/m3) Phosphoric acid (mg/m3)
Canada Labour Code 0.2 [thoracic] 1; 3 [stel]
AB, NB, QC 1; 3 [stel] 1; 3 [stel]
BC, MB, NL, NS, ON, PE 0.2 [thoracic] 1; 3 [stel]
NT, NU, SK 0.2; 0.6 [stel, thoracic] 1; 3 [stel]
YT 1; 1 [stel] 1; 3 [stel]
Other Jurisdiction    
ACGIH 2020 TLV 0.2 [thoracic] 1; 3 [stel]
mg/m3 = milligrams per cubic meter
stel = short term exposure limit (15 min. maximum)
thoracic = vapour particle size in thoracic fraction

Main Uses

Mists from strong inorganic acids are not used by industry directly, but may be produced as a result of industrial processes.[1]

Inorganic acids, including sulfuric acid, are used in many industrial processes that have the potential to generate acid mists.[2] In the US, 60-70% of sulfuric acid is used to produce fertilizers, where phosphate rock is converted to phosphoric acid.[1] Sulfuric acid is also used in the following industries: pulp and paper, iron and steel (for pickling, cleaning, and etching metals), lead-acid battery manufacturing, petroleum refining, mining and metallurgy, ore processing, synthetic rubber and plastics, soap and detergents, water treatment, cellulose fibers and films, and inorganic pigments and paints.[1]

Canadian Production and Trade

Several organizations produce and distribute inorganic chemicals such as sulfuric acid in Canada, including Chemtrade, and ERCO Worldwide.[19] Canada exports the majority of its sulphuric acid to the United States.[19]

Production and trade

Activity Quantity Year
Import: 123,343 t of ‘sulphuric acid’ 2021[20]
Export: 1,904,834 t of ‘sulphuric acid’ 2021[20]

Occupational Exposures Overview

Exposure to mists from strong inorganic acids may occur through inhalation, ingestion, and dermal contact, although inhalation is the most important route of exposure.[1,3]

Workers with the greatest potential for high exposure are those involved in manufacturing, using, and transporting sulfuric acid, isopropanol, and oleum (fuming sulfuric acid), as well as those in metal pickling.[1,2] Moderate levels of exposure are expected in soap and detergent production, and the manufacture of nitric acid and ethanol.[2] Lower exposure levels are expected in lead-acid battery manufacturing and phosphate fertilizer production.[2] Factors influencing the type and extent of exposure include the industrial process, particle size, distance from the source, control measures (i.e. ventilation), and the breathing pattern of workers.[1,3]

CAREX Canada has not prioritized mists from strong inorganic acids for exposure estimate development. This is because a lack of exposure data precluded it in the past. However, the team is investigating new sources of data and methods in order to potentially address this exposure in the future.


2. International Agency for Research on Cancer (IARC). Monograph summary, Volume 100 Part F (2012) (PDF)
3. Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for Sulfur Trioxide and Sulfuric Acid (1998) (PDF)
9. Government of Newfoundland and Labrador. Regulation 5,12 Occupational Health and Safety Regulations (2018)
10. Government of the Northwest Territories. Occupational Health and Safety Regulations, R-039-2015 (2020) (PDF)
12. The Canadian Legal Information Institute (CanLII). Government of Nunavut’s Occupational Health and Safety Regulations, Nu Reg 003-2016 (2010)
14. Government of Prince Edward Island. Occupational Health and Safety Act Regulations Chapter 0-1 (2013) (PDF)
17. The Canadian Legal Information Institute (CanLII). Yukon’s Occupational Health Regulations, O.I.C. 1986/164 (2020) (PDF)
18. Occupational Safety and Health Administration (OSHA). Annotated PELs (2020)
19. Chemistry Industry Association of Canada. Chemistry industry economic profile (2020) (PDF)
20. International Trade Center. TradeMap (Free subscription required)


Other Resources

  1. Health Canada. WHMIS Quick Facts Sheet: Corrosive Materials (2006) (PDF)
  2. Canadian Centre for Occupational Health and Safety (CCOHS). Health Effects of Sulfuric Acid (2013)

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