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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:

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

Air Transportation

Surface Transportation

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 Consumer Commodity 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 Consumer Commodity 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 Mailable Limited Quantity material per 345

Only ORM–D material per 345

Prohibited

Division 5.2: Organic Peroxides

Only Mailable Limited Quantity material per 345

Only ORM–D material per 345

Prohibited

6

Toxic Substances and Infectious Substances

 

Division 6.1: Toxic Substances

Consumer Commodity 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

7

Radioactive Material

Prohibited

Only per 347

Only registered air letters per 622

8

Corrosives (Liquids And Solids)

Only Mailable Limited Quantity material per 348

Only ORM–D material per 348

Prohibited

9

Miscellaneous Hazardous Materials

Consumer Commodity 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