Sulfur Dioxide

Sulfur dioxide (also sulphur dioxide) is the chemical compound with the formula SO2. [fusion_builder_container hundred_percent=”yes” overflow=”visible”][fusion_builder_row][fusion_builder_column type=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none”][1] It is a colourless gas with a pungent, irritating and rotten odour. [2] Sulfur dioxide is non-flammable and reacts easily with other substances to form harmful compounds, such as sulfuric acid, sulfurous acid and sulfate particles. [3]

Sulfur dioxide in the air results primarily from activities associated with the burning of fossil fuels (coal, oil) such as at power plants or from copper smelting. In nature, it can be released to the air, for example, from volcanic eruptions. [4]


Uses [2]


Sulfur dioxide is used:

  • As a fruit preserving agent and as a food preservative or additive.
  • In the fermentation stage of wine making.
  • For bleaching textile fibres.
  • In the manufacture of paper.
  • As a disinfectant in breweries and food factories.
  • As a fumigant for grains, grapes and citrus fruits.


Sources of Emission & Routes of Exposure


Sources of Emission [2]


  • Industry sources: Fossil fuel combustion sites particularly coal burning power plants; industrial processes such as wood pulping, paper manufacture, petroleum and metal refining and metal smelting, particularly from sulfide containing ores, e.g. lead, silver and zinc ores all emit sulfur dioxide to air.
  • Diffuse sources: Small textile bleaching and food preserving facilities and wineries, fumigation activities all emit sulfur dioxide to air.
  • Natural sources: Geothermal activity, including hot springs and volcanic activity; sulfur dioxide is produced from the natural decay of vegetation on land, in wetlands and in oceans all emit sulfur dioxide to air.
  • Transport sources: Vehicle exhaust.
  • Consumer products: Some solvents, dechlorination agents, bleaches and fumigation products.


Routes of Exposure [4]


Exposure to sulfur dioxide mainly occurs by breathing air that contains it. Exposure may also result from skin contact to sulfur dioxide. The people most often exposed to sulfur dioxide are workers in plants where it occurs as a by-product, such as in the copper smelting industry and in the processing or burning of coal or oil Other exposures occur in the manufacture of sulfuric acid, paper, food preservatives, and fertilisers The primary way that workers are exposed to sulfur dioxide is through the air. Workers may be exposed to concentrations of sulfur dioxide that are higher than typical outdoor air levels. People living near heavily industrial activities that involve smelting copper or the processing or burning of coal or oil are also likely to be exposed to sulfur dioxide by breathing it. If you breathe air containing sulfur dioxide, you may absorb it into your body through your nose and lungs. Sulfur dioxide can easily and rapidly enter your bloodstream through your lungs. Once in the body, it breaks down to sulfate and leaves through the urine


Health Effects [2,4]


Short-term exposures to high levels of sulfur dioxide can be life threatening. Exposure to 100 parts of sulfur dioxide per million parts of air (ppm) is considered immediately dangerous to life and health. Previously healthy non-smoking miners who breathed sulfur dioxide released as a result of an explosion in an underground copper mine developed burning of the nose and throat, breathing difficulties, and severe airway obstructions. Exposure of the eyes to liquid sulfur dioxide, (from, for example an industrial accident) can cause severe burns, resulting in the loss of vision. On the skin it produces burns. Other health effects include headache, general discomfort and anxiety. Those with impaired heart or lung function and asthmatics are at increased risk.


Long-term exposure to persistent levels of sulfur dioxide can also affect your health. Repeated or prolonged exposure to moderate concentrations may cause inflammation of the respiratory tract, wheezing and lung damage. Lung function changes have been observed in some workers exposed to 0.4–3.0 ppm sulfur dioxide for 20 years or more. However, these workers were also exposed to other chemicals, making it difficult to attribute their health effects to sulfur dioxide exposure alone. Additionally, exercising asthmatics are sensitive to the respiratory effects of low concentrations (0.25 ppm) of sulfur dioxide.


Studies in animals support the human data regarding respiratory effects of sulfur dioxide. At low levels (less than 1 ppm) of sulfur dioxide exposure, guinea pigs displayed changes in their ability to breathe as deeply or as much air per breath. More severe symptoms seen in animals exposed to high concentrations of sulfur dioxide include decreased respiration, inflammation or infection of the airways, and destruction of areas of the lung. It has also proved to be harmful to the reproductive systems of experimental animals and caused developmental changes in their newborn.


Safety [5]


First Aid Measures


  • Eye Contact: Immediately flush eyes with plenty of water for at least 15 minutes. Get immediate medical attention.
  • Inhalation: Move exposed personnel to uncontaminated area. If not breathing, administer artificial respiration. If breathing is difficult, administer oxygen. Obtain prompt medical attention and continue with administration of oxygen. If airway obstruction occurs the placement of an artificial airway by an emergency medical technician may be necessary.
  • Skin Contact: Immediately flush with large amounts of water. Remove contaminated clothing, including shoes, after flushing has begun. Applications of ice water compresses for 30 minutes after flushing may help limit extent of burn.
  • Note to Physician: Bronchospasm may be treated with the use of a bronchodilator such as albuterol and an anticholinergic inhalant such as Atrovent.


Exposure Controls & Personal Protection


Engineering Controls


Ventilation: Provide good ventilation and/or local exhaust to prevent accumulation of concentrations above exposure limits.


Personal Protective Equipment


  • Respiratory Protection: Emergency Use: Use SCBA or positive pressure air line with mask and escape pack in areas where concentration is unknown or above the exposure limits.
  • Eye Protection: Safety glasses and face shield.
  • Skin Protection: General Use: Leather gloves, safety shoes, and safety glasses for handling cylinders. Acid resistant gloves and splash suit when connecting, disconnecting, or opening cylinders. Emergency Use: Totally encapsulated chemical resistant suit.
  • CAUTION: Contact with cold, evaporating liquid on gloves or suit may cause cryogenic burns or frostbite. Cold temperatures may also cause embrittlement of PPE material resulting in breakage and exposure.


Regulation [2,6,7]


United States


OSHA Permissible Exposure Limit (PEL) – General Industry
See 29 CFR 1910.1000 Table Z-1
5 ppm
(13 mg/m3) TWA
HE14 Upper respiratory irritation, nosebleeds
OSHA PEL – Construction Industry
See 29 CFR 1926.55 Appendix A
5 ppm
(13 mg/m3) TWA
HE14 Upper respiratory irritation, nosebleeds
OSHA PEL – Shipyard Employment
See 29 CFR 1915.1000 Table Z-Shipyards
5 ppm
(13 mg/m3) TWA
HE14 Upper respiratory irritation, nosebleeds
National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL) 2 ppm
(5 mg/m3) TWA

5 ppm
(13 mg/m3) STEL

HE4 Blindness
HE9 Bronchoconstriction
HE11 Breathing difficulties
HE14 Eye and respiratory irritation, eye and skin burning
American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) (2009) 0.25 ppm
(0.65 mg/m3) STEL


HE9 Bronchoconstriction, exacerbation of asthma
HE10 Decreased lung function, chronic respiratory symptoms
HE11 Lower respiratory irritation and symptoms
HE14 Upper respiratory irritation
(5 mg/m3) TWA

5 ppm
(10 mg/m3) STEL



  • International Agency for Research on Cancer (IARC) carcinogenic classification: Class 3 (not classifiable as to its carcinogenicity to humans)
  • Agency for Toxic Substances and Disease Registry (ATSDR) Inhalation Minimal Risk Level (MRL): 0.01 ppm (acute)
  • NIOSH Immediately Dangerous to Life or Health (IDLH) concentration: 100 ppm




National Ambient Air Quality Standards and Goals:


  • Averaging period 1 hour: Maximum 0.2 parts per million, maximum allowable exceedences: 1 day a year.


  • Averaging period 1 day: Maximum 0.08 parts per million, maximum allowable exceedences: 1 day a year.


  • Averaging period 1 year: Maximum 0.02 parts per million, maximum allowable exceedences: none.


Safe Work Australia:

  • Time Weighted Average Concentration of 2ppm or 5.2 mg/m3 averaged over a 40 hour work week.
  • Short-term Exposure Limit of 5ppm or 13 mg/m3 time weighted average over 15 minutes