Which option best describes readily combustible solids in terms of ignition?

Which option best describes readily combustible solids in terms of ignition?

• A. Solids that remain inert and do not burn.
• B. Materials that ignite by friction, burn faster than 2.2 mm/sec, or metal powders that can be ignited.
• C. Solids that ignite only when heated above 1000 C.
• D. Solids that do not support combustion.

Answer: (B)

Readily combustible solids are those that can ignite easily under practical conditions, not by staying inert. The best description includes materials that can ignite by friction, burn rapidly, or are metal powders that can be ignited. Friction ignition means that simply rubbing or grinding can generate enough heat or sparks to start burning. A rapid burn rate—in excess of a defined threshold like 2.2 mm per second—shows the material isn’t just slow to catch fire but poses an immediate ignition hazard. Metal powders are especially prone to ignition due to their large surface area, which speeds up oxidation and ignition. The other options don’t fit this hazard profile: inert solids that do not burn won’t ignite readily; requiring ignition only above 1000 C is not characteristic of readily combustible solids, which ignite more easily under milder conditions; and solids that do not support combustion clearly aren’t readily combustible.

Readily combustible solids are those that can ignite easily under practical conditions, not by staying inert. The best description includes materials that can ignite by friction, burn rapidly, or are metal powders that can be ignited. Friction ignition means that simply rubbing or grinding can generate enough heat or sparks to start burning. A rapid burn rate—in excess of a defined threshold like 2.2 mm per second—shows the material isn’t just slow to catch fire but poses an immediate ignition hazard. Metal powders are especially prone to ignition due to their large surface area, which speeds up oxidation and ignition.

The other options don’t fit this hazard profile: inert solids that do not burn won’t ignite readily; requiring ignition only above 1000 C is not characteristic of readily combustible solids, which ignite more easily under milder conditions; and solids that do not support combustion clearly aren’t readily combustible.