UN/NA Number Reference
DOT Class 6.1 Toxic Substance placard

UN 1561: Arsenic trioxide

49 CFR 172.101 Hazardous Materials Table·ERG 2024

DOT Classification and Shipping

UN 1561 is assigned the proper shipping name Arsenic trioxide in the U.S. DOT Hazardous Materials Table (49 CFR 172.101). It is classified as a Class 6.1 Toxic Substance material, Packing Group II. Required label(s): 6.1.

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 151)

Hazards: TOXIC. May be fatal if inhaled, ingested, or absorbed through skin. Contact may cause burns.

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

Spill: Do not touch. Avoid inhalation. Use water spray to reduce dust/vapor. Ventilate.

Chemical and Physical Properties

Arsenic trioxide appears as white or transparent, glassy amorphous lumps or crystalline powder. Slightly soluble in water, but dissolves very slowly; more soluble in hot water. Noncombustible. Corrosive to metals in the presence of moisture. Toxic by ingestion.

CAS Number: 1327-53-3
Molecular Formula: As2O3
Molecular Weight: 197.841 g/mol
Color / Form: White cubic crystals (Arsenolite)
Odor: Odorless
Boiling Point: 869 F
Melting Point: 379 to 594.1 °F ; Arsenolite and claudetite forms sublime at 379 °F. (EPA, 1998)
Specific Gravity: 3.738 amorphous or vitreous
Vapor Pressure: 66.1 mmHg at 593.6 F
Water Solubility: Insoluble in water

Regulatory Data

CERCLA RQ (40 CFR 302.4)
1 lb
EPCRA TPQ (40 CFR 355)
100 lb
RCRA Waste Code(s)
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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: IB8, IP2, IP4, T3, TP33. 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 1561 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.