UN/NA Number Reference

UN 3526: Hydrogen selenide, adsorbed

49 CFR 172.101 Hazardous Materials Table·ERG 2024

DOT Classification and Shipping

UN 3526 is assigned the proper shipping name Hydrogen selenide, adsorbed 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, 2.1.

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 119)

Hazards: TOXIC. May be fatal if inhaled or absorbed through skin. Flammable. Vapors heavier than air.

Fire: Small: dry chemical or CO2. Large: water spray or fog. Fight from maximum distance.

Spill: Do not touch. Stop leak if safe. Use water spray to reduce vapor.

Chemical and Physical Properties

Hydrogen selenide is a colorless gas with an offensive odor. It is highly flammable and toxic. It may be irritating to eyes and mucous membranes. It is heavier than air. Long term exposure to low concentrations or short term exposure to high concentrations can result in adverse health effects from inhalation. If exposed to prolonged fire or intense heat the containers may violently rupture or rocket. Rate of onset: Immediate Persistence: Minutes - hours Odor threshold: 0.3 ppm Source/use/other hazard: Metals &semiconductor preparation; highly flammable/explosive; can cause burns/frostbite; decomposes rapidly to form elemental selenium

CAS Number: 7783-07-5

Molecular Formula: H2Se

Molecular Weight: 80.99 g/mol

Color / Form: Colorless gas

Odor: Odor resembling decayed horseradish

Boiling Point: -42 F

Melting Point: -86.31 °F (EPA, 1998)

Flash Point: Flammable gas

Specific Gravity: 2.12 (sinks in water)

Vapor Pressure: 9120 mmHg

Vapor Density: 2.12 (heavier than air)

Water Solubility: 0.9 % at 73 °F (NIOSH, 2024)

pH: Aqueous solution is weakly acidic, although it is stronger than aqueous acetic acid

Regulatory Data

CERCLA RQ (40 CFR 302.4)

1 lb

EPCRA TPQ (40 CFR 355)

10 lb

OSHA PEL

TWA 0.05 ppm (0.2 mg/m 3 )

NIOSH REL

TWA 0.05 ppm (0.2 mg/m 3 )

IDLH

1 ppm

A release of this material at or above its CERCLA reportable quantity (1 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: 1. 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 3526 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.