What does 49 CFR 173.124 (Class 4, Divisions 4.1, 4.2 and 4.3—Definitions) require?

As Ask X3, your fleet-compliance assistant, here is what 49 CFR 173.124 requires and defines for Class 4 materials based on the provided regulation text:

The regulation defines the criteria and types of materials that fall under Class 4, Divisions 4.1, 4.2, and 4.3, specifically focusing on Division 4.1 (Flammable Solids).

Under 49 CFR 173.124, a Flammable Solid (Division 4.1) includes four main types of materials:

1. Desensitized explosives: Class 1 explosives (other than compatibility group A) when dry, which are wetted with sufficient water, alcohol, or plasticizer to suppress their explosive properties, and are specifically authorized by name in the Hazardous Materials Table, through a special permit, or via an approval.

2. Self-reactive materials: Materials that are thermally unstable and can undergo exothermic decomposition without oxygen. These are broken down into seven generic types (Types A through G) based on their physical state, temperature controls, test results, and written approval from the Associate Administrator. Notably:

* Type A materials can detonate or deflagrate rapidly and are forbidden from being transported.

* Type G materials are exempt from Division 4.1 requirements if they are thermally stable (SADT is 50 °C / 122 °F or higher for a 50 kg package).

3. Readily combustible solids: Solids that may cause a fire through friction (such as matches), solids with a burning rate faster than 2.2 mm (0.087 inches) per second, or metal powders that ignite and react over the sample length in 10 minutes or less.

4. Polymerizing materials: Materials that undergo an exothermic reaction forming larger molecules or polymers without stabilization under normal transport conditions, provided their self-accelerating polymerization temperature (SAPT) is 75 °C (167 °F) or less, they exhibit a heat of reaction of more than 300 J/g, and they do not meet the definitions of hazard classes 1–8.