Class 4 Hazards
Class 4 Hazard includes Solid materials that can cause serious risk of fire in uncontrolled conditions in the presence of a source of ignition under standard circumstances i.e., without:
- Artificially changing variables such as pressure or density; or
- Adding accelerants to speed up a chemical process
The hazard class is divided into three categories:
- Flammable Solids
- Spontaneously Combustible
- Water Reactive (also called dangerous when wet)
4.1 Flammable Solids are readily combustible or may contribute to a fire through friction. These include:
- Flammable solids
- Self-reactive substances
- Solid desensitized explosives
E.g.: Metallic sodium and potassium, oily fabrics, matches, and nitrocellulose products
4.2 Spontaneously Combustible materials are also called substances liable to spontaneous combustion which occurs by self-heating (increase in temperature due to exothermic internal reactions), followed by thermal runaway (self heating which rapidly accelerates to high temperatures) and finally, autoignition. These include:
- Pyrophoric substances (highly reactive chemicals that spontaneously ignite when exposed to air). Examples – potassium hydride (KH) and white phosphorus
- Self-heating substances
E.g: Oil-seed products, linseed oil rags, coal dust, hay, wood chips, manure, and latex
4.3 Water Reactive (also called dangerous when wet) substances emit a flammable gas when in contact with water.
E.g.: Alkali metals (e.g., Sodium, Potassium) and metal hydrides (e.g., Lithium aluminum hydride, Sodium hydride)
Reactivity series of Metals:
Order of Reactivity | Metal | Reactions with water or Steam |
Most reactive | Potassium (K) | Very vigorous reaction with cold water |
Second most reactive | Sodium (Na) | Vigorous reaction with cold water |
Third most reactive | Calcium (Ca) | Less vigorous reaction with cold water |
Least reactive | Magnesium (Mg) | Slow reaction with cold water, vigorous with hot water |
