What must not be allowed regarding chain-fused aerial shells during a display?

Chain-fused aerial shells are designed as a single-use device, meaning they are not meant to be reloaded into mortars after being fired. Once they are ignited, they are intended to discharge their effects and cannot be safely reloaded or reused. This is critical for safety and operational integrity, as attempting to reload these shells can lead to failure or unintended ignition, which poses significant risks to both the operators and the spectators. Thus, the prohibition of reloading chain-fused aerial shells into mortars helps ensure the display is conducted safely and effectively under the guidelines set forth in the NFPA 1123.