On a flat roof with built up roofing, which base cannot be used?

In the context of lightning protection systems installed on flat roofs with built-up roofing, the question focuses on identifying a base material that is suitable for the installation of the system.

A wooden base is not ideal for such installations because wood is a combustible material, which can pose a fire risk during a lightning strike. Additionally, wood can deteriorate over time due to exposure to moisture and environmental conditions, compromising the effectiveness of the lightning protection system.

Concrete and metal bases are commonly used in lightning protection. Concrete provides a non-combustible and durable foundation that can support various components of the system without risk of degradation. Metal bases are also effective, as they can facilitate better grounding due to their conductive properties.

The option suggesting that none of these bases cannot be used implies that all listed bases could potentially be suitable under different circumstances. However, the critical consideration here is that wood, due to its combustible nature, is inappropriate for this specific application on flat roofs with built-up roofing.