SO2 Gas and its Sensor

Intro to Sulfur Dioxide

Sulfur dioxide is a chemical compound with the formula SO2. Sulfur dioxide gas is colorless, has an irritating and pungent odor, and is very toxic. As a result, SO2 poses a significant threat in certain workplaces. Prolonged exposure can lead to breathing difficulties, as well as damage to the respiratory tract and can cause . Additionally, sulfur dioxide is very reactive, and often combines with other compounds in the atmosphere. These compounds can increase acid rain and/or haze, both of which present danger. 

Gas Characteristics

  • Colorless
  • Heavier than air  
  • Suffocating, irritating, pungent odour (often described as "burning matchsticks") 
  • If heated, can explode  
  • VERY toxic  
  • Corrosive impact on the respiratory tract  
  • Can make breathing quite difficult 
  • Reacts violently with halogens & strong bases 
  • Also known as sulfurous anhydride and sulfur(IV) oxide and can be spelled sulphur dioxide. 
  • CAS 7446-09-5
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Industrial SO2 hazards and sources

  • Any industry where it is present as a by-product, including copper smelting & power plants  
  • Pulp and paper mills
  • Chemical processing
  • Metal smelting and processing
  • Oil and petroleum refineries  
  • Manufacturing of fertilizers  
  • Manufacturing of sulfuric acid
  • Cement manufacturing
  • Food and beverage processing
  • Glass manufacturing 
  • Sewer and wastewater treatment 
  • Other industrial facilities burning fossil fuels or coal

High concentrations of SO2 can affect lung function, worsen asthma attacks, and worsen existing heart disease in sensitive groups.

(National Park Service)

High Risk Scenarios

  • As sulfur dioxide exposure can make breathing difficult, those with asthma are particularly at risk. 
  • Naturally occurs in smaller quantities in volcanos.
  • Any industrial process that burns coal or petroleum.
  • Automobiles, ships, trains and other fossil-fuel burning methods of transportation will emit it. 
  • Heavy equipment that burns fuel with a high sulfur content is also a common source. 
  • Petroleum production and oil refining have numerous process that can lead to sulfur dioxide exposure.
  • Nearly all production processes involving metals pose a threat (aluminum production, steel production, forging, molding and core making, smelting copper or lead, metal extraction and refining, etc.) 
  • sensor-confined-space-entry-so2Confined space entry hazard: sulfur dioxide is heavier than air so can accumulate in the lower sections of confined spaces.

SO2 Sensor Info

Type: Electrochemical
Range: 0-100ppm (0.1ppm resolution)

Alarm Levels

Low Alarm: 2 ppm
High Alarm: 5 ppm
STEL — 15 minute — Short Term Exposure Limit: 10 ppm
TWA  — 8 hour time weighted average: 2 ppm

Questions about the detection of SO2?

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Special Applications and Considerations

  • High concentrations of SO2 can contribute to acid rain, which is harmful to both humans (can cause and/or worsen the symptoms of respiratory diseases) as well as the environment (damage existing foliage and decrease growth).
  • SO2 can also combine with other compounds in the atmosphere to create haze, which can be extremely harmful to the lungs & heart.

Health Risks and Handling of SO2

concentration
symptoms/effects
0.3 - 1 ppm
Possible detection by taste or smell
1 - 2 ppm
Lung function changes, symptoms for asthmatics likely to increase in severity
3 - 5 ppm
Easily detected odor
6 - 12 ppm
May cause nasal/throat irritation
10 - 19 ppm
Respiratory irritation, nosebleeds possible
20 - 49 ppm
Significant irritation to the eyes, chronic respiration symptoms will develop, respiratory protection is necessary
50 - 100 ppm
After 30 - 60 minutes, will be life-threatening
100 ppm +
Immediately life-threatening
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FIRST AID
  • If INHALED, move the impacted person to fresh air, and prevent them from moving around unnecessarily.
  • If breathing is difficult, trained staff should provide emergency oxygen.
  • Call poison control or a doctor IMMEDIATELY and transport the victim to a hospital.
  • If SKIN CONTACT is made, gently apply lukewarm water to the impacted area for 5 minutes and call poison control/a doctor (if the affected area is the eyes, ensure the victim's eyelids are open).
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IF ACCIDENTALLY RELEASED
  • Wear chemical-protective clothing, as well as safety goggles and a face shield. 
  • If you are wearing the necessary safety equipment, remove the sulphur dioxide from the area if possible. 
  • Ventilate the impacted area as much as possible. 
  • Try and knock down sulphur dioxide gas with fog or fine water spray - be aware, the resulting sulfuric acid is corrosive and toxic.
  • If the leak is very large or difficult to control, contact local emergency services.

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