Sulphuric acid is a dense oily liquid clear to dark brown in colour. It mixes with water in all proportions and is corrosive and non‐flammable.
Sulphuric acid is used in the manufacture of chemicals, detergents, dyes, explosives and fertilisers. It is the acid in lead acid batteries. Sulphuric
acid is also used in metal cleaning and electroplating, and solutions of metal sulphates and sulphuric acid are used in the electrowinning of
metals.
The current SWA WES for sulphuric acid mist is a time weighted average (TWA) value of 1 mg/m3, based on the 1991 American Conference of
Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV®).
Sulphuric acid mists have been long recognised as corrosive to teeth and irritant to the respiratory system. In 1992, the International Agency
for Research on Cancer (IARC) classified strong acid mists containing sulphuric acid as known to be carcinogenic to humans (Category 1).
In 2001, the United Kingdom Health and Safety Executive (UK HSE) issued a Chemical Hazard Alert Notice based on research done by the
European Sulphuric Acid Association, advising that the occupational exposure standard of 1.0 mg/m3 may not protect against chronic
inflammation of the larynx. It was suggested that exposure to sulphuric acid be reduced to below 0.3 mg/m3 in order to control against
inflammation. In 2004, the ACGIH issued a revised TLV® of 0.2 mg/m3 measured as thoracic particulate mass, but maintained an A2 Suspected
Human Carcinogen rating.
In 2007, the European Commission’s Scientific Committee on Occupational Exposure Limits (SCOEL) reviewed the available OELs for sulphuric
acid mist. From animal studies they noted “evidence of slight changes in the laryngeal epithelium at the lowest concentration tested, 0.3 mg/m3.
Other experimental studies in a range of animal species suggest respiratory tract effects on repeated exposure to concentrations around 0.3
mg/m3, with the possibility of effects of some health significance even at concentrations down to about 0.1 mg/m3”. They concluded that “long‐
term exposure should be maintained below 0.1 mg/m3 in order to provide sufficient reassurance of avoidance of possible adverse consequences
for the respiratory tract epithelium. Hence SCOEL recommends an 8h TWA limit of 0.05 mg/m3 in order to satisfy this requirement”.
In 2012, SCOEL added Annex 2 Sampling aspects to their documentation. Based on the aerosol size of acid mists and the target organ including
the upper respiratory tract and larynx, SCOEL concluded that sampling should be as the inhalable fraction of airborne aerosol. The AIOH concurs
with this. Collection of the acid aerosol on a quartz fibre filter for analysis by ion chromatography is also recommended.
Studies of the carcinogenicity of sulphuric acid mist have frequently been undertaken without exposure measurements and with potential
confounding exposures not well accounted for. In a review of 25 epidemiology studies a moderate association was found between exposure to
sulphuric acid mist and laryngeal cancer. However, while the data suggest a dose‐response relationship, the biological plausibility and the
possible carcinogenic mechanism remained uncertain.
Non‐malignant respiratory effects exist at 1 to 3 mg/m3 while short‐term reduced lung clearance rates were observed at 0.1 mg/m3. Worker
exposure to about 0.5 mg/m3 has been reported to cause an average of 5 acute effect symptoms (e.g. sneezing, irritated nose, cough, runny
nose and dry nose). Practical experience within the AIOH Exposure Standards Committee members has found exposure to 0.1 mg/m3 is clearly
perceptible, 0.2 mg/m3 can cause coughing, sneezing and shortness of breath while exposure to 1 mg/m3 is intolerable to many people.
Chronic effects have been noted in rats exposed at 0.5 and 1.0 mg/m3 but effects at 0.2 mg/m3 were minimal. A review of animal studies found
effects noted in several species at exposure levels above 1 mg/m3 while effects were not noted at 0.1 mg/m3.
The TWA occupational exposure limit for sulphuric acid mist recommended by the AIOH is 0.1 mg/m3, to be measured as the inhalable aerosol
fraction according to AS 3640. This standard is set to minimise the incidence of irritant and respiratory effects and of laryngeal cancer. A
recommended STEL of 0.5mg/m3 is feasible but may not be particularly useful in its purpose of warning of possible acute effects, considering
delay in reporting due to the requirements of laboratory analysis of collected samples. There is no doubt that such a level causes acute health
effects even after a single short term exposure, to which the usual response in most people is withdrawal from the exposure or use of respiratory
protection.
Currently, no feasible biomarker is available to be used for biological monitoring.
