The hazard class of a hazardous material is indicated either by its class (or division) number, its class name, or by the letters “ORM-D”. The following table lists class numbers, division numbers, class or division names and those sections of this subchapter which contain definitions for classifying hazardous materials, including forbidden materials.
| Class No. | Division No. (if any) | Name of class or division | 49 CFR reference for definitions |
|---|---|---|---|
| None | Forbidden materials | 173.21 | |
| None | Forbidden explosives | 173.54 | |
| 1 | 1.1 | Explosives (with a mass explosion hazard) | 173.50 |
| 1 | 1.2 | Explosives (with a projection hazard) | 173.50 |
| 1 | 1.3 | Explosives (with predominately a fire hazard) | 173.50 |
| 1 | 1.4 | Explosives (with no significant blast hazard) | 173.50 |
| 1 | 1.5 | Very insensitive explosives; blasting agents | 173.50 |
| 1 | 1.6 | Extremely insensitive detonating substances | 173.50 |
| 2 | 2.1 | Flammable gas | 173.115 |
| 2 | 2.2 | Non-flammable compressed gas | 173.115 |
| 2 | 2.3 | Poisonous gas | 173.115 |
| 3 | Flammable and combustible liquid | 173.120 | |
| 4 | 4.1 | Flammable solid | 173.124 |
| 4 | 4.2 | Spontaneously combustible material | 173.124 |
| 4 | 4.3 | Dangerous when wet material | 173.124 |
| 5 | 5.1 | Oxidizer | 173.127 |
| 5 | 5.2 | Organic peroxide | 173.128 |
| 6 | 6.1 | Poisonous materials | 173.132 |
| 6 | 6.2 | Infectious substance (Etiologic agent) | 173.134 |
| 7 | Radioactive material | 173.403 | |
| 8 | Corrosive material | 173.136 | |
| 9 | Miscellaneous hazardous material | 173.140 | |
| None | Other regulated material: ORM-D | 173.144 |
[Amdt. 173-224, 55 FR 52606, Dec. 21, 1990, as amended at 57 FR 45460, Oct. 1, 1992; Amdt. 173-234, 58 FR 51531, Oct. 1, 1993]