Which of the following are examples of Class 4 flammable solids?

Which of the following are examples of Class 4 flammable solids?

• A. Magnesium, sulfur, and calcium carbide
• B. Gasoline
• C. Nitric acid
• D. Water

Answer: (A)

Class 4 covers solids that can ignite easily or release flammable gases. Magnesium and sulfur are classic flammable solids—they burn readily when exposed to heat or flame, so they fit in this category. Calcium carbide is a water-reactive solid; when it meets water it rapidly releases acetylene, a highly flammable gas, which also puts it in Class 4 (specifically the water-reactive subset). Gasoline is a liquid—flammable liquids are Class 3, not Class 4. Nitric acid is an oxidizer and corrosive; it’s Class 5.1, not a flammable solid. Water isn’t flammable at all and has no such classification.

Class 4 covers solids that can ignite easily or release flammable gases. Magnesium and sulfur are classic flammable solids—they burn readily when exposed to heat or flame, so they fit in this category. Calcium carbide is a water-reactive solid; when it meets water it rapidly releases acetylene, a highly flammable gas, which also puts it in Class 4 (specifically the water-reactive subset).

Gasoline is a liquid—flammable liquids are Class 3, not Class 4. Nitric acid is an oxidizer and corrosive; it’s Class 5.1, not a flammable solid. Water isn’t flammable at all and has no such classification.