Sulphur dioxide / SO₂

Sulphur dioxide

Gas Identification

Other denomination
sulphurous oxide, sulphurous anhydride, sulphur oxide
CAS Registry Number
SCBA type

Chemical properties

Molecular formula
Molecular mass
64,1 g/mol

Physical properties

Boiling point
-10 °C
Autoignition temperature
Gas/Vapour density
12,3 eV

Flammability limit


Threshold limit value

2 ppm │ À partir de juillet 2020 : 0,5 ppm • 1,3 mg/m³
5 ppm │ À partir de juillet 2020 : 1 ppm • 2,7 mg/m³

Sulphur dioxide : Description and use


Sulphur dioxide, once also known as sulphurous anhydride, is a colourless gas with a strong, pungent and suffocating odour. Detectable from 0.45 ppm, its presence can be identified before reaching the occupational exposure limit (2 ppm) and the short-term exposure limit (5 ppm).
However, odour alone cannot be considered an appropriate or trustworthy warning sign of dangerous exposure levels, a measuring instrument must be used to identify the product and measure the concentration.
Furthermore, sense of smell varies form person to person. It is released into Earth's atmosphere by volcanoes and by many industrial processes, as well as when certain coals, oils and natural gases that are not sulphur free are burned. The oxidisation of sulphur dioxide, most often in the presence of catalysts such as nitrogen dioxide (NO₂), produces sulphur trioxide (SO₃) and sulphuric acid (H₂SO₄), which is how acid rain forms. It can cause inflammation of the respiratory tract.
It is a colourless gas or a liquefied compressed gas with a pungent odour.


This product is used in several practices and in various industries, here are a few examples:

  • Chemical products (sulphuric acid, sulphites, potassium and sodium hydrosulphites, thiosulphates)
  • Refining ores and metals
  • Soy proteins
  • Bleaching agent for oils and starches
  • Sulphonation of oils
  • Disinfecting and fumigating
  • Food additive (to delay browning, enzymatic reaction, bacterial growth)
  • Reducing agent
  • Antioxidant

Sulphur dioxide : Warnings and caution

GHS hazard statements

H314 - Causes severe skin burns and eye damage.
H331 - Toxic if inhaled.

GHS precautionary statements

P280 - Wear protective gloves/protective clothing/eye protection/face protection.
P305+P351+P338 - IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
P310 - Immediately call a POISON CENTRE or doctor/physician
P321 - Specific treatment (see ... on this label).
P403+P233 - Store in a well-ventilated place. Keep container tightly closed.

SGH04 : Gaz sous pression
SGH06 : Toxique
SGH05 : Corrosif