What material should not be used to construct salute shells larger than 3 inches?

The material that should not be used to construct salute shells larger than 3 inches is metal. Salute shells are designed to produce a loud report upon ignition, and their construction must be carefully managed to ensure safety during handling, storage, and firing.

Using metal for larger salute shells poses significant risks. Metals can potentially shatter upon detonation due to the high pressure and force generated inside the shell. This shattering can lead to projectile hazards, increasing the likelihood of injury to spectators and personnel during a fireworks display.

In contrast, other materials such as wood, glass, and ceramic may have their own limitations but do not carry the same severity of danger as metal in the context of larger salute shells. For instance, while those materials can also break or shatter, they do not have the same structural rigidity that could lead to lethal projectiles in the same way that metal might. Hence, the specific guidance in NFPA 1123 emphasizes avoiding metal for larger salute shell constructions to prioritize safety during fireworks displays.