33 Hazard Classes

331 Nine Classes

Every hazardous material is assigned to one of nine hazard classes as defined in 49 CFR 172.101 and 173. The nine hazard classes are as follows:

Class 1: Explosives.
Class 2: Gases.
Class 3: Flammable and Combustible Liquids.
Class 4: Flammable Solids.
Class 5: Oxidizing Substances, Organic Peroxides.
Class 6: Toxic Substances and Infectious Substances.
Class 7: Radioactive Materials.
Class 8: Corrosives.
Class 9: Miscellaneous Hazardous Materials.

Some of the nine classes are further separated into divisions based on their physical or chemical properties, as shown in Exhibit 331.

Exhibit 331

DOT Hazard Classes and Postal Mailability

Class	Name of Hazard Class (and Division when applicable)	Domestic Mail		International Mail and APO/FPO Mail
Class	Name of Hazard Class (and Division when applicable)	Air Transportation	Surface Transportation	International Mail and APO/FPO Mail
1	Explosives
	Division 1.1: Mass Explosive Hazard	Prohibited	Prohibited	Prohibited
	Division 1.2: Projection Hazard	Prohibited	Prohibited	Prohibited
	Division 1.3: Fire and/or Minor Blast/Minor Projection Hazard	Prohibited	Prohibited	Prohibited
	Division 1.4: Minor Explosion Hazard	Prohibited	Only with prior HQ approval per 341	Prohibited
	Division 1.5: Very Insensitive With Mass Explosion Hazard	Prohibited	Prohibited	Prohibited
	Division 1.6: Extremely Insensitive; No Mass Explosion Hazard	Prohibited	Prohibited	Prohibited
2	Gases
	Division 2.1: Flammable Gases	Prohibited	Only ORM–D material per 342	Prohibited
	Division 2.2: Nonflammable Gases	Only ORM–D material per 342	Only ORM–D material per 342	Prohibited
	Division 2.3: Toxic Gases	Prohibited	Prohibited	Prohibited
3	Flammable and Combustible Liquids
	All Flammable Liquids	Prohibited	Only ORM–D material per 343	Prohibited
	All Combustible Liquids	Only ORM–D material per 343	Only ORM–D material per 343	Prohibited
4	Flammable Solids
	Division 4.1: Flammable Solids	Prohibited	Only ORM–D material per 344	Prohibited
	Division 4.2: Spontaneously Combustible	Prohibited	Only ORM–D material per 344	Prohibited
	Division 4.3: Dangerous When Wet	Prohibited	Only ORM–D material per 344	Prohibited
5	Oxidizing Substances, Organic Peroxides
	Division 5.1: Oxidizing Substances	Only ORM–D material per 345	Only ORM–D material per 345	Prohibited
	Division 5.2: Organic Peroxides	Only ORM–D material per 345	Only ORM–D material per 345	Prohibited
6	Toxic Substances and Infectious Substances
	Division 6.1: Toxic Substances	ORM–D material per 346; other poisons as permitted in 346.231	ORM–D material per 346; other poisons as permitted in 346.231	Prohibited
	Division 6.2: Infectious Substances	Only as permitted in 346	Only as permitted in 346	Only registered air letters per 622

Exhibit 331

DOT Hazard Classes and Postal Mailability

Class	Name of Hazard Class (and Division when applicable)	Domestic Mail		International Mail and APO/FPO Mail
Class	Name of Hazard Class (and Division when applicable)	Air Transportation	Surface Transportation	International Mail and APO/FPO Mail
7	Radioactive Material	Prohibited	Only per 347	Only registered air letters per 622
8	Corrosives (Liquids And Solids)	Only ORM–D material per 348	Only ORM–D material per 348	Prohibited
9	Miscellaneous Hazardous Materials	ORM–D material and other materials as permitted in 349	ORM–D material and other materials as permitted in 349	Prohibited, except for magnetized materials per 349 and 622.4