Sulfur Dioxide Safety: Exposure Limits and Prevention

This document outlines the permissible exposure limits (PEL) for sulfur dioxide (SO2) and details the safety measures necessary to prevent overexposure. It is based on industry best practices and guidelines to ensure workplace safety.

Permissible Exposure Limits (PELs)

ACGIH® Recommended Exposure Limit

The American Conference of Governmental Industrial Hygienists (ACGIH®) recommends a Threshold Limit Value (TLV®) - Short-term Exposure Limit (STEL) [C] of 0.25 ppm for sulfur dioxide. This is a ceiling limit, meaning it should not be exceeded at any time. The A4 notation indicates that it is 'Not classifiable as a human carcinogen'. [1] [1]

Canadian Jurisdictions

In many Canadian jurisdictions, the exposure limits are similar to the ACGIH® TLVs®. Exact details vary by jurisdiction, so local occupational health and safety departments should be contacted for specific information. [1]

Safety Measures to Prevent Overexposure

Engineering Controls

The primary method for controlling sulfur dioxide exposure is through engineering controls. These include:

• Local exhaust ventilation and enclosure to control the amount of sulfur dioxide in the air.
• Stringent control measures such as process enclosure to prevent product release into the workplace.
• A corrosion-resistant exhaust ventilation system separate from other ventilation systems.
• Exhaust directly to the outside, taking necessary precautions for environmental protection.
• Provision of eyewash and safety showers where contact or splash hazards exist.

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Personal Protective Equipment (PPE)

When engineering controls are not sufficient to maintain exposure below the PEL, personal protective equipment (PPE) must be used. Appropriate PPE for sulfur dioxide includes:

• Chemical safety goggles and face shield when contact is possible.
• Chemical protective clothing such as gloves, aprons, and boots. Suitable materials include Viton®, Viton®/butyl rubber, Kemblok ®, Saranex®ᵀM, Chemprotex® 300, ChemMAX® (3, 4 Plus), AlphaTec® (4000, EVO, VPS), Tychem® (9000, Responder CSM, 10000, 10000FR) Zytron® 500. Natural rubber and nitrile rubber are not recommended.
• Respiratory protection, with specific respirator types depending on the concentration of sulfur dioxide. Refer to the NIOSH Pocket Guide to Chemical Hazards for more information.

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Respiratory Protection Levels

The following respiratory protection levels are recommended based on sulfur dioxide concentration:

• Up to 20 ppm: Any chemical cartridge respirator with cartridge(s) providing protection against sulfur dioxide; or Any supplied-air respirator.
• Up to 50 ppm: Any supplied-air respirator operated in a continuous-flow mode; Any powered, air-purifying respirator with cartridge(s) providing protection against the compound of concern.
• Up to 100 ppm: Any chemical cartridge respirator with a full facepiece and cartridge(s) providing protection against the compound of concern; Any air-purifying, full-facepiece respirator (gas mask) with a chin-style, front- or back-mounted canister providing protection against the compound of concern; Any powered, air-purifying respirator with a tight-fitting facepiece and cartridge(s) providing protection against the compound of concern; Any supplied-air respirator that has a tight-fitting facepiece and is operated in a continuous-flow mode; Any self-contained breathing apparatus with a full facepiece; Any supplied-air respirator with a full facepiece.

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Handling and Storage

• Secure cylinders in an upright position and protect them from damage. Use a suitable hand truck to move cylinders; do not drag, roll, slide, or drop.
• Keep containers tightly closed when not in use or empty. Use corrosion-resistant tools and equipment.
• Store in a cool, dry, well-ventilated, and temperature-controlled area, separate from incompatible materials, out of direct sunlight and away from heat and ignition sources.
• Restrict access to authorized personnel only.
• Have escape-type respiratory protective equipment readily available in case of leaks or spills.
• Always secure cylinders in an upright position to a wall, rack, or other solid structure.
• Store empty containers separately and keep them closed, as they may contain hazardous residue.

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Unintentional Release Measures

• In the event of a spill or leak, immediately put on escape-type respirator and exit the area.
• Report leaks, spills, or failures of safety equipment immediately.
• Get medical attention for all exposures; symptoms can be delayed.
• Use personal protective equipment as required.
• Increase ventilation to the area or move the leaking container to a well-ventilated and secure area.
• Stop or reduce the leak if safe to do so.
• Knock down gas with fog or fine water spray. Be aware that the resulting sulfuric acid solutions are very corrosive and toxic.
• Dike and recover contaminated water for appropriate disposal.
• Contact the supplier and local fire and emergency services for help.

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First Aid Measures

Inhalation:

Inhalation

Take precautions to ensure your own safety before attempting rescue (e.g., wear appropriate protective equipment). Move victim to fresh air. If breathing is difficult, trained personnel should administer emergency oxygen. If breathing has stopped, trained personnel should begin artificial respiration (AR). DO NOT allow victim to move about unnecessarily. Symptoms of pulmonary edema may be delayed. Get medical attention immediately. Treatment is urgently required. Transport to a hospital. [2]

Skin Contact:

Skin Contact

Gas: flush with gently flowing water Get medical attention. Liquefied gas: quickly remove victim from source of contamination. DO NOT attempt to rewarm the affected area on site. DO NOT rub area, flush with water, or apply direct heat. Carefully cut around clothing that sticks to the skin and remove the rest of the garment. Do not remove frozen clothing from frostbitten areas. Loosely cover the affected area with a sterile dressing. DO NOT allow victim to drink alcohol or smoke. Get medical attention immediately. Treatment is urgently required. Transport to a hospital. Double bag, seal, label and leave contaminated clothing, shoes, and leather goods at the scene for safe disposal. [2]

Eye Contact:

Eye Contact

Gas: move victim to fresh air. Immediately flush the contaminated eye(s) with gently flowing water, occasionally lifting the upper and lower eyelids. Liquefied gas: avoid direct contact. Wear chemical protective gloves if necessary. Immediately flush with gently flowing water. DO NOT attempt to rewarm. Cover both eyes with a sterile dressing. DO NOT allow victim to drink alcohol or smoke. Get medical attention immediately. Treatment is urgently required. Transport to a hospital. [2]

Ingestion:

Ingestion

Not applicable (gas). [2]

Stability and Reactivity Hazards

• Normally stable.
• Avoid water, moisture, or humidity.
• Incompatible with halogens (e.g., chlorine) and strong bases (e.g., sodium hydroxide).
• Corrosive to aluminum alloys and carbon steel in the presence of water.
• On reaction with water: sulfurous acid solution.

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