What must be done when air terminals exceed 24 inches in height according to safety regulations?

When air terminals exceed a height of 24 inches, they require additional support or stabilization to ensure their structural integrity and effectiveness in a lightning protection system. The need for bracing is based on safety regulations aimed at preventing potential failure due to wind loads or other environmental forces that can impact tall structures. Bracing ensures that the air terminal remains securely in place and functions properly to intercept and convey lightning safely to the ground without posing a danger to nearby structures or individuals.

This regulation is critical because an unsecured or unstable air terminal could lead to a failure in the lightning protection system, increasing the risk of damage or fire from a lightning strike. The other options may touch on aspects of safety or performance but do not directly address the specific requirement for additional structural support for taller air terminals.