What minimum size is specified for a manhole opening in a boiler?

The specified minimum size for a manhole opening in a boiler is 11 x 15 inches. This dimension is critical for ensuring safety and maintenance accessibility. A manhole of this size allows personnel to safely enter and exit the boiler for inspection, cleaning, and repairs, which is essential for both operational efficiency and employee safety.

In the context of boiler design and safety regulations, it is important that manhole openings are large enough to accommodate not only personnel but also tools and equipment that may be necessary for maintenance tasks. Additionally, having a manhole of this size helps ensure that workers have enough room to maneuver without risk of injury.

The other options provided do not meet the standard size requirements necessary for safe entry and accessibility into a boiler, and therefore are not suitable for this application.