Which of the following is not acceptable material for the base of a boiler?

The use of compacted earth as a base for a boiler is not acceptable due to several critical reasons related to structural integrity and safety. A boiler operates under high pressure and temperature, generating significant weight and requiring a stable foundation to support it adequately. Compacted earth may not provide the necessary level of stability and durability, especially over time, as it can shift or settle, leading to improper alignment of the boiler and potential hazards such as leaking or even catastrophic failures.

In contrast, materials such as concrete and steel are commonly accepted for boiler bases because they offer the strength and stability required for heavy equipment. Concrete is especially popular due to its compressive strength and resistance to environmental factors, while steel provides robustness and can support heavy loads when designed appropriately. Wood, while not ideal, may sometimes be used in temporary or less critical applications; however, its characteristics are not suitable for long-term boiler support. Using solid and durable materials ensures that the boiler operates safely and effectively without risks associated with foundation failure.