Which of the following materials may NOT be used for air terminals?

The correct answer indicates that zinc should not be used as a material for air terminals in lightning protection systems. This is primarily because zinc, while it has some beneficial properties, does not have the necessary electrical conductivity and corrosion resistance required for effective lightning protection. Air terminals must have high conductivity to ensure that lightning strikes are safely conducted to the ground, preventing damage to structures.

Copper, aluminum, and steel are commonly used materials for air terminals because they possess the required conductive and mechanical properties. Copper is well-known for its excellent conductivity and resistance to corrosion, making it a preferred choice. Aluminum is lightweight and also effectively conducts electricity. Steel, when properly treated or coated, can serve as a durable option for air terminals, though its conductivity is lower than that of copper and aluminum.

In summary, the capability of a material to effectively conduct electricity and resist corrosion is vital for it to function properly as an air terminal, making zinc an unsuitable choice in this context.