# NIOSH Pocket Guide to Chemical Hazards
Sulfur dioxide | CAS 7446-09-5
SO2 | RTECS WS4550000
Synonyms & Trade Names Sulfurous acid anhydride, Sulfurous oxide, Sulfur oxide | DOT ID & Guide 1079 125
Exposure Limits | NIOSH REL: TWA 2 ppm (5 mg/m3) ST 5 ppm (13 mg/m3)
OSHA PEL†: TWA 5 ppm (13 mg/m3)
IDLH 100 ppm | Conversion 1 ppm = 2.62 mg/m3
Physical Description Colorless gas with a characteristic, irritating, pungent odor. [Note: A liquid below 14°F. Shipped as a liquefied compressed gas.]
MW: 64.1 | BP: 14°F | FRZ: -104°F | Sol: 10%
VP: 3.2 atm | IP: 12.30 eV | RGasD: 2.26 |
Fl.P: NA | UEL: NA | LEL: NA |
Nonflammable Gas
Incompatibilities & Reactivities Powdered alkali metals (such as sodium & potassium), water, ammonia, zinc, aluminum, brass, copper [Note: Reacts with water to form sulfurous acid (H2SO3).]
Measurement Methods NIOSH 6004; OSHA ID104, ID200
Personal Protection & Sanitation Skin: Frostbite Eyes: Frostbite Wash skin: No recommendation Remove: When wet or contaminated (liquid) Change: No recommendation Provide: Frostbite | First Aid (See procedures) Eye: Frostbite Skin: Frostbite Breathing: Respiratory support
Respirator Recommendations NIOSH Up to 20 ppm: (APF = 10) Any chemical cartridge respirator with cartridge(s) providing protection against the compound of concern*/(APF = 10) Any supplied-air respirator* Up to 50 ppm: (APF = 25) Any supplied-air respirator operated in a continuous-flow mode*/(APF = 25) Any powered, air-purifying respirator with cartridge(s) providing protection against the compound of concern* Up to 100 ppm: (APF = 50) Any chemical cartridge respirator with a full facepiece and cartridge(s) providing protection against the compound of concern/(APF = 50) Any air-purifying, full-facepiece respirator (gas mask) with a chin-style, front- or back-mounted canister providing protection against the compound of concern/(APF = 50) Any powered, air-purifying respirator with a tight-fitting facepiece and cartridge(s) providing protection against the compound of concern*/(APF = 50) Any supplied-air respirator that has a tight-fitting facepiece and is operated in a continuous-flow mode*/(APF = 50) Any self-contained breathing apparatus with a full facepiece/(APF = 50) Any supplied-air respirator with a full facepiece Emergency or planned entry into unknown concentrations or IDLH conditions: (APF = 10,000) Any self-contained breathing apparatus that has a full facepiece and is operated in a pressure-demand or other positive-pressure mode/(APF = 10,000) Any supplied-air respirator that has a full facepiece and is operated in a pressure-demand or other positive-pressure mode in combination with an auxiliary self-contained positive-pressure breathing apparatus Escape: (APF = 50) 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 appropriate escape-type, self-contained breathing apparatus
Exposure Routes inhalation, skin and/or eye contact
Symptoms Irritation eyes, nose, throat; rhinorrhea (discharge of thin mucus); choking, cough; reflex bronchoconstriction; liquid: frostbite
Target Organs Eyes, skin, respiratory system
See also: INTRODUCTION