UN/NA Number Reference
DOT Class 2.3 Toxic Gas placard

UN 2197: Hydrogen iodide, anhydrous

49 CFR 172.101 Hazardous Materials Table·ERG 2024

DOT Classification and Shipping

UN 2197 is assigned the proper shipping name Hydrogen iodide, anhydrous in the U.S. DOT Hazardous Materials Table (49 CFR 172.101). It is classified as a Class 2.3 Toxic Gas material. Required label(s): 2.3, 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 125)

Hazards: TOXIC. Corrosive. Causes burns. May be fatal if inhaled. Vapors heavier than air.

Fire: Use water spray or fog. Do not get water inside containers.

Spill: Fully encapsulating suit required. Stop leak if safe. Use water spray.

Chemical and Physical Properties

Hydriodic acid appears as a colorless to yellow liquid with a pungent odor. Consists of a solution of hydrogen iodide in water. Fumes irritate the eyes and mucous membranes. Corrosive to metals and to tissue.

CAS Number: 10034-85-2
Molecular Formula: HI
Molecular Weight: 127.9124 g/mol
Color / Form: Colorless gas; fumes in moist air
Odor: Acrid
Boiling Point: -35.1 C
Melting Point: -50.8 °C
Specific Gravity: 5.66 g/L
Vapor Pressure: 5,938 mm Hg at 25 C
Vapor Density: 4.4 (heavier than air)
Water Solubility: Extremely soluble in water

Special Provisions

49 CFR 172.102 special provision codes for this entry: 3, B14, N86, N89. 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 2197 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.