A manhole is an opening structure for personnel entry and exit, used for installation, maintenance, and safety inspections of equipment. It primarily consists of short筒节 (or short tube), flanges, and a handle-equipped manhole cover. Regarding safety inspections, pressure vessels require a specific number and size of manholes, which are detailed in the "inspection openings." Manhole materials include carbon steel and stainless steel. Manholes are categorized into atmospheric and pressure manholes based on the pressure conditions; into round, elliptical, and rectangular manholes based on shape, with rectangular manholes being suitable only for atmospheric pressure equipment; and into horizontal and vertical installation manholes based on their installation position. Manhole cover fastening methods include swing covers and lifting covers; the opening speed of manholes can be standard or quick. Manhole structures and dimensions are generally standardized, allowing selection or design based on relevant manuals.