DOT Class 4: Flammable Solids, Spontaneously Combustible and Dangerous When Wet
DOT Class 4 covers three kinds of solid or reactive materials: Division 4.1 flammable solids, Division 4.2 spontaneously combustible materials, and Division 4.3 materials that are dangerous when wet. Each has its own label color and its own packing group rules.
How it is defined
- Division 4.1 includes readily combustible solids, self-reactive materials, solid desensitized explosives and polymerizing substances.
- Division 4.2 includes pyrophoric materials (ignite in air within about five minutes) and self-heating materials.
- Division 4.3 includes materials that react with water to give off flammable or toxic gas.
- Packing groups reflect how severe the hazard is, and are I (high), II (medium) and III (low). Not all Class 4 entries use all three.
Summary of 49 CFR Parts 171 to 180. The regulations and the Hazardous Materials Table (49 CFR 172.101) control any shipment.
Label and placard
- Colors
- Red and white stripes (4.1), white over red (4.2), blue (4.3)
- Symbol
- Flame in each case
Three different diamonds, one for each division. See the division pages for the colors.
Packing groups
Packing groups I, II and III are used in Class 4 (not all in each division). PG I is the greatest danger and PG III the least. How packing groups work.
Common examples
- Matches, sulfur and nitrocellulose (4.1)
- White phosphorus, some metal powders (4.2)
- Sodium, potassium, calcium carbide (4.3)
How it relates to GHS
Class 4 maps to several GHS physical hazard classes: flammable solids, self-reactive substances, pyrophoric liquids and solids, self-heating substances and substances that emit flammable gases on contact with water.
- GHS: Flammable solids
- GHS: Self-reactive substances and mixtures; Organic peroxides
- GHS: Pyrophoric liquids
- GHS: Pyrophoric solids
- GHS: Self-heating substances and mixtures
- GHS: Substances and mixtures which in contact with water, emit flammable gases
DOT classes and GHS classes are assigned under different rules, so a product can have different severity labels in each. See also all GHS hazard classes.
Safe handling reminders
- Store 4.3 materials dry and away from water sources and sprinklers where appropriate.
- Keep 4.2 materials away from air as the SDS specifies, for example under inert gas or oil.
- Use class D extinguishers or other media listed in Section 5 for metal fires; never use water on 4.3 fires.
Where to find it on an SDS
Section 14 shows the class and division (4.1, 4.2 or 4.3), UN number, packing group and ERG guide number. Look in Section 14: Transport information. Hazard classification for the workplace is in Section 2. You can also see how a UN number points to a response guide on the UN and NA numbers page.
Divisions in Class 4
Frequently asked questions
What are the three divisions of DOT Class 4?
4.1 is flammable solids (including self-reactive substances), 4.2 is spontaneously combustible materials, and 4.3 is materials that are dangerous when wet.
General reference only. It does not replace the supplier's SDS or the current federal regulations.