Glossary / Physical hazards
Flammable solid
A flammable solid is a solid that is easily ignited and burns rapidly, or that may cause or contribute to fire through friction. Powders and granules are especially sensitive because their surface area lets flame spread fast.
Explanation
The GHS tests solids by burning rate: a material is classed as flammable if it ignites readily after a short contact with a flame and the fire spreads quickly. Examples include some metal powders, sulfur-type materials, matches and certain nitrocellulose products. Categories are based on whether the flame also crosses a wetted zone.
Physical form matters as much as chemistry. A block of metal may be hard to ignite while the same metal as fine powder burns violently. Dust clouds can also explode, a related but separate danger, so housekeeping that prevents dust accumulation is part of the control strategy.
In transport, DOT Class 4 covers flammable solids along with substances liable to spontaneous combustion and those that are dangerous when wet. These divisions overlap with other terms in this glossary, such as pyrophoric and water-reactive materials, which behave differently around air and water.
Storage should be cool and dry, separated from oxidizers and ignition sources. Choose extinguishing agents with care, because water is wrong for some metal powders while it works for many ordinary flammable solids. The SDS spells this out.
What to do and watch for
- Avoid generating dust and clean it up with methods that do not create sparks.
- Keep away from oxidizers, heat and friction sources.
- Confirm the right extinguishing agent before an emergency, not during one.
Where it appears on an SDS
- Section 2: Hazard identification. Flammable solid category, flame pictogram and hazard statements H228.
- Section 5: Fire-fighting measures. Extinguishing media that are suitable or prohibited, and fire-fighting precautions.
SDS content and wording vary by supplier. This page is general reference and does not replace the current SDS for your product.