Which of the following boiler components is primarily for visual inspection access?

Handholes are specifically designed for visual inspection access on a boiler. They are smaller openings that provide access to the interior of the boiler, enabling operators and maintenance personnel to check for internal conditions such as fouling, corrosion, and overall system integrity without requiring extensive disassembly. This visual inspection capability is crucial for ensuring safe operation and identifying maintenance needs at an early stage.

The steam space, while allowing for monitoring of steam pressure and quality, does not provide access for visual inspection of the components within the boiler. The combustion pass pertains to the path that flue gases take through the boiler, relevant to efficiency and emissions, rather than for inspection purposes. Diagonal stays are structural components that help support the boiler but do not facilitate visual access. Thus, handholes are the clear and specific components employed to allow for visual checks and maintenance inspections in boiler operations.