4 stars based on
A manhole cover is a removable plate forming the lid over the opening of a manholeto prevent anyone or anything from falling in, and to keep out unauthorized persons and material. Manhole covers date back at least to the era of ancient Rome, which had sewer grates made from stone.
Manhole covers are often made out of cast ironconcrete or a combination of the two. The weight helps to keep them in place when traffic passes over them, cap and trade program design options f900 makes it difficult for unauthorised people without suitable tools to remove them.
Manhole covers may also be made from glass-reinforced plastic or other composite material especially in Europe, or where cover theft is of concern. Because of law restricting acceptable manual handling weights, Europe has seen a move towards lighter weight composite manhole cover materials, which also have the benefits of greater slip resistance and electrical insulating properties.
A manhole cap and trade program design options f900 sits on a metal base, with a smaller inset rim which fits the cover. The base and cover are sometimes called "castings", because they are usually made by a casting processtypically sand-casting techniques. The covers usually feature "pick holes", into which a hook handle tool is inserted to lift them.
Pick holes can be concealed for a more watertight lid, or can allow light to shine through. A manhole pick or hook cap and trade program design options f900 typically used to lift them, though other tools can be used as well, including electromagnets. Although the covers are too large to be easily collectibletheir ubiquity and the many patterns and descriptions printed on them has led some people to collect pictures of covers from around the world.
Despite their weight and cumbersome nature, manhole covers are sometimes stolenusually for resale as scrap, particularly when metal prices rise.
The question of why manhole covers are typically round in some countries was made famous by Microsoft when they cap and trade program design options f900 asking it as a job-interview question. Other manhole shapes can be found, usually squares or rectangles.
NashuaNew Hampshiremay be unique in the United States for having triangular manhole covers that point in the direction of the underlying flow. The city is phasing out the triangles, which were made by a local foundrybecause they are not large enough to meet modern safety standards and a manufacturer for larger triangles cannot be found.
Some triangular water-main covers also exist in San Francisco. Because of concerns about unauthorized access to underground spaces, manhole covers may be locked down, or even temporarily spot-welded in place.
This practice has become routine in some locales, as advance preparation for official parades and similar cap and trade program design options f900 attracting large crowds or important people. In urban areas, stray voltage issues have become a significant concern for utilities. InJodie S. Lane was electrocuted after stepping on a metal manhole cover, while walking her dog in New York City. Because of their aerodynamic design, some modern racing cars create enough vacuum to lift a manhole cover off its recess.
During races on city streets, manhole covers must therefore be welded or locked down to prevent injury. This caused the trailing Porsche to catch fire, and safety issues ended the race shortly afterwards. According to urban legenda manhole cover was accidentally launched from its shaft during an underground nuclear test in the s, at high enough speed to achieve escape velocity. A calculation before the cap and trade program design options f900 gave a predicted speed of six times Earth escape velocitybut the calculation is not likely to have been accurate.
After the event, Dr. Brownlee described the best estimate of the cover's speed from the photographic evidence as "going like a bat out of hell! A robotics research paper in suggested that robots could examine the shapes of specific manhole covers and use them to calculate their geographic position, as a double-check on GPS data. The European norm EN of applies to manhole and gully tops with a clear opening up to 1 m for areas subjected to pedestrian or vehicular traffic covers with a clear opening over 1 m are specified in the British Standard BS for example.
The lightest class A15 cast iron manhole cover can withstand a maximum weight of 1. It would typically be restricted to light duty applications in pedestrian areas, gardens, patios, driveways and similar. The heaviest F class manhole cover would typically be used in docks, airports and other extreme heavy-duty applications.
It has a similar scope as the ENfocuses on wheel loadings and is based on the European standards for structural steelwork. The FACTA specification applies to solid top covers, recessed covers designed for structural or non-structural infill and surface drainage products. From Wikipedia, the free encyclopedia. Urban exploration and Stray voltage. How Products are Madeenotes.
China DailyDecember 21, Accessed December 19, Flint JournalJuly 14, Archived from the original on Nashua TelegraphAug. Lane Public Safety Foundation. Brownlee - June ". Retrieved September 28, Glossary of road transport terms Road types by features.
Retrieved cap and trade program design options f900 " https: Street furniture Public utilities Subterranea geography Road hazards.
Webarchive template wayback links All articles with dead external links Articles with dead external links from May All articles with unsourced statements Articles with unsourced statements from March Articles with unsourced statements from January cap and trade program design options f900 Views Read Edit View history.