UNunnums
3531

UN 3531Polymerizing substance, solid, stabilized, n.o.s.

Division 4.1

Flammable solids

Summary

UN 3531 is the UN number for polymerizing substance, solid, stabilized, n.o.s. It is classed in Division 4.1 (flammable solids) of Class 4 for transport. Packing group III. Emergency responders use ERG guide 149P.

Emergency response

The Emergency Response Guidebook (ERG2024) guide for this number:

  • Guide149PPolymerizing substance, solid, stabilized, n.o.s.

A “P” after the guide number means the material may suffer a violent polymerization.

From the 2024 Emergency Response Guidebook (ERG2024), published by U.S. Department of Transportation, PHMSA. Read the full guide in the ERG or on CAMEO Chemicals.

Identification

UN number
UN 3531
Name
Polymerizing substance, solid, stabilized, n.o.s.
Hazard class
Class 4: Flammable solids
Division
4.1: Flammable solids
Packing group
III
What the class covers
Flammable solids, self-reactive substances and solid desensitized explosives.

U.S. Hazardous Materials Table

The entry for this number in 49 CFR 172.101.

  • UN3531Polymerizing substance, solid, stabilized, n.o.s.

    • Technical name required in parentheses

    Special provisions: 387, IB7, IP19, N92, T7, TP4, TP6, TP33

    Class
    4.1
    Packing group
    III
    Labels
    4.1

From the eCFR edition of 49 CFR 172.101 dated 2026-10-05 (section last amended 2026-09-08). The eCFR is an editorial compilation, not the official legal edition. Read the current table.

About Class 4

Class 4 covers flammable solids and other substances that can catch fire. Division 4.1 is flammable solids and self-reactive substances, 4.2 is substances that can spontaneously combust in air, and 4.3 is substances that give off flammable gas when wet.

See all Class 4 UN numbers

Check the official sources

For emergency response, packaging and quantity limits, use these: