Which type of mortars should not be intermixed during a display?

Intermixing mortars of various sizes during a fireworks display can lead to significant safety hazards. Each mortar is designed to accommodate specific shell sizes, and using shells that do not match the mortar size can cause malfunctions or even catastrophic failures. For example, if a smaller shell is placed in a larger mortar, it may not function properly, leading to unpredictable flight paths or premature ignition.

Additionally, different mortar sizes can have varying ignition characteristics, which can disrupt the timing and sequence of the display, impacting its overall safety and aesthetics. Therefore, to ensure the safety of the display and maintain control over the performance of fireworks, only mortars of the same size should be used together. This practice helps to prevent the risks associated with misfire or malfunction, thereby enhancing the safety for both the operators and the spectators.