What material is NOT safe to use in a fire?

The material that is not safe to use in a fire is paper or cardboard. When these materials ignite, they can produce a significant amount of smoke and toxic fumes, which can greatly hinder visibility and pose serious health risks in a fire scenario. Additionally, paper and cardboard can easily catch fire and burn quickly, contributing to the spread of the fire and increasing its intensity.

In contrast, metal and glass don't typically combust or support combustion in the same way. Metals can withstand high temperatures without burning, although they may conduct heat and become dangerous when heated. Glass, on the other hand, is neither flammable nor combustible; rather, it can withstand high heat without contributing to the fire. While plastics can melt and emit toxic fumes when burned, it’s generally understood that paper or cardboard poses a higher risk in terms of ignitability and the potential to fuel a fire rapidly.