UN/NA Number Reference
DOT Class 3 Flammable Liquid placard

UN 1991: Chloroprene, stabilized

49 CFR 172.101 Hazardous Materials Table·ERG 2024

DOT Classification and Shipping

UN 1991 is assigned the proper shipping name Chloroprene, stabilized in the U.S. DOT Hazardous Materials Table (49 CFR 172.101). It is classified as a Class 3 Flammable Liquid material, Packing Group I. Required label(s): 3, 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 131)

Hazards: HIGHLY FLAMMABLE. TOXIC. May be fatal if inhaled, swallowed, or absorbed through skin. Vapors heavier than air.

Fire: Small: dry chemical, CO2, water spray, alcohol-resistant foam. Large: water spray, fog, alcohol-resistant foam.

Spill: Eliminate ignition sources. Do not touch. Stop leak if safe. Use vapor-suppressing foam. Ventilate area.

Chemical and Physical Properties

Chloroprene, stabilized appears as a clear colorless liquid. Flash point is very low. May polymerize exothermically if heated or contaminated. If polymerization takes place inside a container, the container may rupture violently. Less dense than water. Vapors heavier than air. Used to make neoprene rubber.

CAS Number: 126-99-8
Molecular Formula: C4H5Cl
Molecular Weight: 88.53 g/mol
Color / Form: Colorless liquid
Odor: Pungent, ether-like odor
Boiling Point: 139 F
Melting Point: -202 °F (NTP, 1992)
Flash Point: -4 F
Autoignition: 440 °C
Specific Gravity: 0.9583
Vapor Pressure: 118 mmHg
Vapor Density: 3 (heavier than air)
Water Solubility: Slightly soluble (NTP, 1992)
Log P: 2.2 (calculated)

Regulatory Data

CERCLA RQ (40 CFR 302.4)
100 lb
OSHA PEL
TWA 25 ppm (90 mg/m 3 ) [skin]
NIOSH REL
Ca C 1 ppm (3.6 mg/m 3 ) [15-minute]
IDLH
Ca [300 ppm]

A release of this material at or above its CERCLA reportable quantity (100 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: 387, B57, T14, TP2, TP13. 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 1991 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.