Sulfur Dioxide

What is Sulfur Dioxide?

Sulfur dioxide (also sulphur dioxide) is the chemical compound with the formula SO2. It is a colourless gas with a pungent, irritating and rotten odour. Sulfur dioxide is non-flammable and reacts easily with other substances to form harmful compounds, such as sulfuric acid, sulfurous acid and sulfate particles.

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.

What is Sulfur Dioxide used for?

Sulfur dioxide is used:

As a fruit-preserving agent and as a food preservative or additive.
In the fermentation stage of winemaking.
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.

Sulfur Dioxide Hazards

Source of Emission

Industry sources: Sulfur dioxide is emitted from coal-burning power plants and industrial processes like wood pulping, paper manufacturing, petroleum refining, and metal refining or smelting, particularly from sulfide-containing ores (e.g., lead, silver, and zinc).

Diffuse sources: Small textile bleaching and food-preserving facilities, wineries, and fumigation activities also emit sulfur dioxide.

Natural sources: Geothermal activity (e.g., hot springs and volcanoes) and the decay of vegetation on land, in wetlands, and in oceans release sulfur dioxide.

Transport sources: Vehicle exhaust contributes to sulfur dioxide emissions.

Consumer products: Certain solvents, dechlorination agents, bleaches, and fumigation products emit sulfur dioxide.

Routes of Exposure

Exposure to sulfur dioxide mainly happens by breathing air that contains it. Skin contact can also result in exposure. Workers in industries such as copper smelting or coal burning are most commonly exposed, often through the air. People living near such industries can also inhale sulfur dioxide. Once in the body, sulfur dioxide enters the bloodstream through the lungs and is excreted in the urine.

Health Effects

Acute Effect

High levels of sulfur dioxide can be life-threatening. Exposure to 100 ppm is considered immediately dangerous. Symptoms include nose and throat irritation, breathing difficulties, and airway obstruction. Eye exposure can cause burns and vision loss, while skin contact can cause burns. Other symptoms include headaches, discomfort, and anxiety. People with asthma or impaired heart/lung function are at higher risk.

Chronic Effects

Prolonged exposure to moderate levels of sulfur dioxide can cause respiratory inflammation, wheezing, and lung damage. Asthmatics are sensitive to even low levels (0.25 ppm). Animal studies also show respiratory issues and lung damage from exposure, along with potential reproductive and developmental harm.

Sulfur Dioxide Safety

First Aid Measures

Eye contact: Flush eyes with water for at least 15 minutes and get medical attention.

Inhalation: Move to fresh air. If breathing is difficult, provide oxygen and seek medical help. Artificial airways may be required for severe cases.

Skin contact: Flush with water and remove contaminated clothing. Apply ice water compresses if necessary.

Sulfur Dioxide Safety Handling

Engineering Controls

Ensure good ventilation or local exhaust to avoid exceeding exposure limits.

Personal Protective Equipment

Respiratory protection: Use a self-contained breathing apparatus (SCBA) in emergency situations or when exposure limits are exceeded.
Eye protection: Safety glasses and face shields.
Skin protection: Use leather gloves, safety shoes, and glasses when handling cylinders. In emergencies, wear an acid-resistant suit and gloves.

Caution: Contact with cold liquid sulfur dioxide may cause burns or frostbite, and low temperatures can damage protective equipment.

Regulations

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) TWA5 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) STELA4	HE9	Bronchoconstriction, exacerbation of asthma
		HE10	Decreased lung function, chronic respiratory symptoms
		HE11	Lower respiratory irritation and symptoms
		HE14	Upper respiratory irritation
CAL/OSHA PELs	2 ppm (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

Australia

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/m³averaged over a 40 hour work week.
Short-term Exposure Limit of 5ppm or 13 mg/m³ time weighted average over 15 minutes