Class 4 — Flammable solids, spontaneously combustible, and dangerous-when-wet substances
Summary
Division 4.1 flammable solids ignite by friction or heat (matches, sulfur, magnesium, solid fuel for camping stoves, naphthalene mothballs, nitrocellulose tablets); Division 4.2 spontaneously combustible substances ignite when exposed to air at normal temperatures (oily rags, white phosphorus, certain catalysts, some metal alloys); Division 4.3 substances dangerous when wet emit flammable gases or ignite on contact with water (calcium carbide, alkali metals, alkaline-earth alloys). Class 4 is the second most-restricted hazmat class for passenger air transport behind Class 1 explosives, with most divisions forbidden in passenger baggage of any kind. Container damage and accidental water exposure are the principal risks.
Packing / quantity notes
Safety-match booklet: one on-person only; spares prohibited. Strike-anywhere matches prohibited in all baggage globally.
Examples
- Safety matches (one book permitted on-person only)
- Strike-anywhere matches (prohibited)
- Solid fuel tablets for camping stoves
- Phosphorus