A manhole is an opening structure used for personnel entry and exit, facilitating installation, maintenance, and safety inspections. It primarily consists of short tube sections (or short pipes), flanges, and a handle-equipped manhole cover. Considering safety inspections, pressure vessels require a specified number of manholes and their small dimensions can be found in "Inspection Holes." Manhole materials include carbon steel and stainless steel. Manholes are categorized as atmospheric and pressurized based on pressure conditions; as circular, elliptical, and rectangular based on shape, with rectangular manholes being suitable only for atmospheric equipment; and as horizontal and vertical installations based on installation position. The types of manhole cover fastening include swing covers and lift covers. The opening speed of manholes can be standard or quick. Manhole structures and dimensions are generally standardized and can be selected or designed according to relevant manuals.