UN/NA Number Reference
DOT Class 8 Corrosive placard

UN 1833: Sulfurous acid

49 CFR 172.101 Hazardous Materials Table·ERG 2024

DOT Classification and Shipping

UN 1833 is assigned the proper shipping name Sulfurous acid in the U.S. DOT Hazardous Materials Table (49 CFR 172.101). It is classified as a Class 8 Corrosive material, Packing Group II. Required label(s): 8.

Packing group indicates the degree of danger within a hazard class: PG I is high danger, PG II medium, PG III low. The proper shipping name, hazard class, UN number, and packing group together form the basic shipping description that must appear on shipping papers and, where required, on the package and placard.

Emergency Response (ERG Guide 154)

Hazards: TOXIC. Corrosive. Non-combustible but may decompose producing toxic fumes when heated.

Fire: Use agent appropriate for surrounding fire. Cool containers.

Spill: Do not touch. Avoid inhalation. Use water spray to reduce fumes.

Chemical and Physical Properties

Sulfurous acid appears as a colorless liquid with a pungent burning sulfur odor. Corrosive to metals and tissue.

CAS Number: 7664-93-9
Molecular Formula: H2O3S
Molecular Weight: 82.08 g/mol
Color / Form: Colorless, oily liquid
Odor: Odorless
Boiling Point: 554 °F at 760 mmHg (EPA, 1998)
Melting Point: 50.65 °F (EPA, 1998)
Autoignition: Not flammable (USCG, 1999)
Specific Gravity: 1.841 (EPA, 1998) - Denser than water; will sink
Vapor Pressure: 1 mmHg at 294.8 °F (EPA, 1998)
Vapor Density: 3.4 (EPA, 1998) - Heavier than air; will sink (Relative to Air)
Water Solubility: 558.5 mg/mL
pH: 1 N solution = 0.3; 0.1 N solution = 1.2; 0.01 N solution = 2.1

Regulatory Data

CERCLA RQ (40 CFR 302.4)
1000 lb
EPCRA TPQ (40 CFR 355)
1000 lb
OSHA PEL
1 0.1 mg/m 3 (ST) 3 mg/m 3
NIOSH REL
TWA 1 mg/m 3
IDLH
15 mg/m 3

A release of this material at or above its CERCLA reportable quantity (1000 lb) requires immediate notification to the National Response Center at 800-424-8802.

Special Provisions

49 CFR 172.102 special provision codes for this entry: B3, IB2, T7, TP2. These codes modify the general requirements (packaging, quantity limits, exceptions) for this specific material. Look up each code in 49 CFR 172.102 for the full text.

Need the full interactive record? Open UN 1833 in the SpillNerd lookup tool for the live database entry with placard graphics, GHS pictograms, full segregation tables, and synonym search. For another material, use the UN number and chemical lookup.

Reference data compiled from the DOT Hazardous Materials Table (49 CFR 172.101), the 2024 Emergency Response Guidebook, and public chemical databases (PubChem, NIOSH, EPA). Always verify the correct shipping description against the current regulation and the manufacturer's SDS Section 14 before shipping.