A manhole is a chamber providing access for maintenance workers to service drains, sewers and other utilities underground. Manhole covers conceal the entrance to the chamber.
Most manhole covers are made from very strong ductile cast iron. Because of its strength, ductile cast iron allows vehicles to travel over manhole covers without them breaking or bowing and people can walk over them safely. Manhole covers can also be made from pressed steel and plastic.
Inspection covers and access plates
Inspection covers and access plates are other names for manhole covers. They can be various sizes and are part of different underground systems, like water, sewerage, electricity and television systems.
An inspection plate or inspection cover leads to an inspection chamber, usually no more than 450mm (17.5 inches) wide and no more than 600mm (24 inches) deep. They are either circular or rectangular and can be opened with a manhole key.
Access chambers are large enough to allow a person to rod drains or carry out other maintenance.
Manholes are the largest chambers. A person is able to access the underground system through the entrance. Manholes can be of any depth but the opening usually measures 600 x 900mm (62 x 35 inches). Their covers are usually made from heavy cast iron and they have keyways and prising slots (gaps where a crow bar can be inserted to loosen the cover before lifting.)
Plastic manhole covers
Some manhole covers are made of polypropylene which is a lightweight and durable plastic; they are usually found in domestic driveways or pedestrian areas. They are opened and closed by way of screws or a lightweight plastic key, supplied with the manhole cover. Some people choose to fit this type of manhole cover because the initial cost is minimal. As a result, they are of no scrap value, so they are less likely to be stolen.