UN/NA Number Reference
DOT Class 2.3 Toxic Gas placard

UN 1660: Nitric oxide, compressed

49 CFR 172.101 Hazardous Materials Table·ERG 2024

DOT Classification and Shipping

UN 1660 is assigned the proper shipping name Nitric oxide, compressed 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, 5.1, 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 124)

Hazards: TOXIC. Oxidizer. May accelerate fire. Corrosive. May cause severe burns.

Fire: Use water spray or fog. Do not use dry chemical or CO2. Cool containers.

Spill: Do not touch. Stop leak if safe. Keep combustibles away from spilled material.

Chemical and Physical Properties

Nitric oxide appears as a colorless gas. Noncombustible but accelerates the burning of combustible material. Vapors heavier than air. Very toxic by inhalation and skin absorption. Heating the containers may cause them to rupture violently and rocket.

CAS Number: 10102-43-9
Molecular Formula: NO
Molecular Weight: 31.014 g/mol
Color / Form: COLORLESS GAS; BLUE LIQ
Odor: Sharp, sweet odor
Boiling Point: -241.1 °F at 760 mmHg (EPA, 1998)
Melting Point: -262.5 °F (EPA, 1998)
Specific Gravity: 1.27 at -238.36 °F (EPA, 1998) - Denser than water; will sink
Vapor Pressure: 26000 mmHg at 68 °F (EPA, 1998)
Vapor Density: 1.04 (EPA, 1998) - Heavier than air; will sink (Relative to Air)
Water Solubility: 5 % (NIOSH, 2024)
Log P: 0

Regulatory Data

CERCLA RQ (40 CFR 302.4)
10 lb
EPCRA TPQ (40 CFR 355)
100 lb
OSHA PEL
TWA 25 ppm (30 mg/m 3 )
NIOSH REL
TWA 25 ppm (30 mg/m 3 )
IDLH
100 ppm
RCRA Waste Code(s)
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A release of this material at or above its CERCLA reportable quantity (10 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, B77. 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 1660 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.