Which of the following is NOT a requirement for air terminals?

The requirement that air terminals must be at least 6 feet tall is not a standard specification for air terminals. Air terminals, often referred to as lightning rods, are intended to provide a path for the discharge of electrical energy from lightning strikes to the ground safely. While their height can contribute to effectiveness in some scenarios, there is no universal requirement mandating that they must be at least six feet tall.

Air terminals must be firmly attached to ensure they function properly during a lightning strike and resist weather conditions. Being made of copper is a common practice due to copper's excellent electrical conductivity, corrosion resistance, and durability. Additionally, visibility from the ground is crucial for ensuring that they are appropriately placed and maintained, allowing for proper installation and inspection. Thus, the other options align with established safety protocols, while the height requirement does not reflect a standard safety guideline.