Hazmat UN Number Lookup

Search hazardous materials database, check safety specifications, and view Emergency Response guides.

🏷️ Primary Hazard Class Filter

UN2421

Nitrogen trioxide

Gases

Class 2.3 (Primary)Class 5.1 (Subsidiary)Class 8 (Subsidiary)

CAS Registry7727-37-9

Hazchem / EAC2XE

ERG Guide Number123

49 CFR Placards & Labels

Toxic GasClass 2.3

⇩ SVG

OxidizerClass 5.1

⇩ SVG

CorrosiveClass 8

⇩ SVG

Not listed as a Reportable Quantity (RQ) hazardous substance under §172.101 Appendix A.

Not listed as a Marine Pollutant under §172.101 Appendix B.

Regulatory Facts

Packing Group

—

Symbols (col 1)

—

Labels (col 6)

2.3, 5.1, 8

PIH Zone

—

Packaging references (49 CFR §173.xxx)

Exceptions (col 8A)

None

Non-Bulk (col 8B)

§173.336

Bulk (col 8C)

§173.245

Aircraft quantity limits (col 9)

Passenger / Rail (9A)

Forbidden

Cargo Aircraft Only (9B)

Forbidden

Vessel stowage (col 10)

Location (10A)

Other codes (10B)

40, 89, 90

Special provisions (col 7 — §172.102)

Hazard Classification & Risks

Class 2.3 — Gas poisonous by inhalation; toxic or corrosive to humans (49 CFR §173.115). Presents an inhalation hazard.

Transport Regulations

Hazard class 2.3. Placard/label codes: 2.3, 5.1, 8. Special provisions: 1. Packaging (49 CFR §173): exceptions §None, non-bulk §336, bulk §245. Quantity limits: passenger aircraft/rail Forbidden, cargo aircraft only Forbidden. Vessel stowage: D (other: 40, 89, 90). Classified per 49 CFR §172.101.

Shortcuts:

p Printd SVGc Copy Names Copy Spilla Copy First-Aid

Source & sourcing note

Regulatory data mirrors the U.S. 49 CFR §172.101 Hazardous Materials Table and companion columns (packaging, quantity limits, vessel stowage, special provisions) as published by the U.S. Pipeline and Hazardous Materials Safety Administration (PHMSA).

Emergency-response content is drawn from the 2024 Emergency Response Guidebook (ERG), a joint publication of PHMSA, Transport Canada, and Mexico’s SCT.

The U.S. edition of the ERG and all U.S. federal regulations are public-domain works under 17 U.S.C. §105. Descriptions on this page are plain-English paraphrases; for any compliance decision, consult the authoritative text on eCFR Title 49 and the ERG at PHMSA.dot.gov. “ERG™” is attributed to PHMSA / Transport Canada / SCT and used nominatively.

Regulatory Facts

Packing Group

—

Symbols (col 1)

—

Labels (col 6)

2.3, 5.1, 8

PIH Zone

—

Packaging references (49 CFR §173.xxx)

Exceptions (col 8A)

None

Non-Bulk (col 8B)

§173.336

Bulk (col 8C)

§173.245

Aircraft quantity limits (col 9)

Passenger / Rail (9A)

Forbidden

Cargo Aircraft Only (9B)

Forbidden

Vessel stowage (col 10)

Location (10A)

Other codes (10B)

40, 89, 90

Special provisions (col 7 — §172.102)

Source & sourcing note

Emergency-response content is drawn from the 2024 Emergency Response Guidebook (ERG), a joint publication of PHMSA, Transport Canada, and Mexico’s SCT.