Agent Name

Sulfur trioxide

CAS Number




Major Category

Toxic Gases & Vapors


Sulfan; Sulfur oxide; Sulfur trioxide, stabilized; Sulfuric anhydride; Sulfuric oxide; Sulphur trioxide; Sulfur trioxide, inhibited or Sulfur trioxide, stabilized; Sulfur trioxide, uninhibited; [ChemIDplus] UN1829


Other Toxic Gases & Vapors


Colorless to white solid that fumes in air at room temperature; [HSDB] Exists in 3 modifications; The alpha and beta forms are solids; mp = 62.3 and 32.5 deg C, respectively; The gamma form is a solid or liquid with a mp of 16.8 deg C; [Merck Index]


Used as a sulfonating agent in the production of detergents and an intermediate in the production of sulfuric acid and explosives; [HSDB]


Highly corrosive to skin; [Quick CPC] Can cause severe coughing at a concentration of 1 ppm; [HSDB] When dry, rapidly absorbs moisture from air evolving dense white fumes; Reacts explosively with water forming sulfuric acid; [Merck Index] The "Human carcinogen" designation refers to sulfuric acid contained in strong inorganic acid mists; [IARC] A strong oxidant that poses a fire and explosion hazard on contact with organic materials; Corrosive to skin, eyes, and respiratory tract; Repeated or prolonged exposure to aerosol may cause effects to the lungs and erosion of teeth; [ICSC] Concentrations of 1 ppm may cause coughing, choking, and severe discomfort; Causes severe burns to skin and eyes; Inhalation causes severe irritation and may cause pulmonary edema; Causes erosion and discoloration of teeth; Health effects basically the same as those for sulfuric acid; [IUCLID] Causes diffuse hepatitis, changes in bronchi, and other endocrine changes in inhalation lethal-concentration studies of guinea pigs; [RTECS] See "Sulfuric acid."

Exposure Assessment


Vapor Pressure

433 mm Hg

Lethal Concentration

LCLo (guinea pig) = 30 mg/m3/6hr

Explanatory Notes

Vapor pressures at 25 deg C: alpha = 73 mm Hg; beta = 344 mm Hg; gamma = 433 mm Hg; [Merck Index]

Adverse Effects
Toxic Pneumonitis



Hepatotoxin, Secondary


Skin Burns

IARC Carcinogen

Known Carcinogen

Links to Other NLM Databases
Health Studies

Human Health Effects from Hazardous Substances Data Bank:

Toxicity Information


Chemical Information

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Occupational diseases associated with exposure to this agent: