HAZMAT Class 5 Oxidizing agents and organic peroxides

An oxidizer is a chemical that readily yields oxygen in reactions, thereby causing or enhancing combustion.

Divisions

An oxidizer is a material that may, generally by yielding oxygen, cause or enhance the combustion of other materials.

A solid material is classed as a Division 5.1 material if, when tested in accordance with the UN Manual of Tests and Criteria, its mean burning time is less than or equal to the burning time of a 3:7 potassium bromate/cellulose mixture.
A liquid material is classed as a Division 5.1 material if, when tested in accordance with the UN Manual of Tests and Criteria, it spontaneously ignites or its mean time for a pressure rise from 690 kPa to 2070 kPa gauge is less than the time of a 1:1 nitric acid /cellulose mixture.

An organic peroxide is any organic compound containing oxygen in the bivalent -O-O- structure and which may be considered a derivative of hydrogen peroxide, where one or more of the hydrogen atoms have been replaced by organic radicals, unless any of the following paragraphs applies:

The material meets the definition of an explosive as prescribed in subpart C of this part, in which case it must be classed as an explosive
The material is forbidden from being offered for transportation according to 49CFR 172.101 of this subchapter or 49CFR 173.21;
The Associate Administrator for Hazardous Materials Safety has determined that the material does not present a hazard which is associated with a Division 5.2 material; or
The material meets one of the following conditions:

Prior to 2007, the placard for 'Organic Peroxide' was entirely yellow, like placard 5.1.