What is the primary characteristic of a handheld firing unit?

The primary characteristic of a handheld firing unit is that it includes two switches: one to arm the unit and another to initiate the firing. This design provides a safety feature, ensuring that the user can safely prepare the unit for operation before actually igniting the fireworks. Arming the unit allows for a precautionary step, enabling the operator to confirm everything is ready before firing. This two-step process minimizes accidental discharges, as the operator must consciously initiate each action, thereby enhancing safety protocols in accordance with NFPA 1123 standards.

The other characteristics represented in the options do not accurately reflect the operational design or safety features of handheld firing units as defined in NFPA guidelines. For example, the absence of switches would compromise safety, while automatic operation could lead to unintended discharges. Furthermore, although remote control can be an option for some firing systems, the handheld unit specifically relies on the operator's direct control via the switches to ensure safety and precision in the firing process.