What is Manhole Cover?

Introduction

A maintenance hole cover, also known as a maintenance hole cover, is a detachable plate that forms the lid over the opening of a maintenance hole, an access point for an underground vault or pipe that is wide enough for a person to pass through. It is made to keep out unauthorized people and objects and prevent anyone from falling in.

Description

Maintenance hole coverings have been around since the Romans, who used stone sewage grates. Cast iron, concrete, or a combination are frequently used to create maintenance hole covers. They are strong, heavy, and typically weigh over 113 kilograms.

Maintenance hole coverings can also be built of composite materials like glass-reinforced plastic (especially in Europe or where cover theft is of concern). Europe has experienced a shift toward lighter-weight composite maintenance hole cover materials because of laws limiting allowable manual handling weights. These materials also offer higher slip resistance and electrical insulating qualities.

A metal base with a tiny inset rim that fits a manhole cover rests beneath the surface. Because they are often created by a casting process, typically sand-casting techniques, the base and lid are occasionally referred to as “castings.”

The covers typically have “pick holes” that can be used with a hook-handled tool to raise them. Pick holes can be covered to create a more watertight lid, or they can be left open to let light through. They are typically lifted using a maintenance hole pick or hook, but other instruments, such as electromagnets, may also be employed. Unfortunately, the covers are too big to be easily collected. Still, because they are so common and have many different designs and information printed, some people have started compiling images of covers worldwide. 95% of Japanese towns, many of which include vibrant inlaid paint on their surfaces, have their designs, claims Remo Camerota, the author of the book on the topic called Trainspotting. Manhole covers are sometimes stolen despite their size and difficulty, mainly to be sold as scrap metal, especially when metal prices are high.

Manhole covers may be labeled to identify the services provided below them and the organization responsible for their maintenance, such as the local water system, telecommunications company, subway or railway services, or natural gas company. In addition, sometimes, the word “manhole” is altered to something more gender-neutral. For instance, the city of Berkeley in California changed the term’s official usage to “maintenance hole” in 2019.

Shapes

Circular – Microsoft made the query of why manhole covers are typically round (in some nations) famous by starting to use it as a question during employment interviews. The problem was initially intended to test a person’s psychological response to questions with multiple possible solutions. However, it has since given rise to various other interpretations, ranging from the philosophical to the tautological (“Manhole covers are round because manholes are round”).

Possible causes of the shape include:

• A round manhole cover may fall in if installed diagonally in the hole, but a round manhole cover cannot fall through its round opening. 
• A “lip” supports the lid, so the underlying hole must be smaller than the cover for alternative shapes to work. Although spherical coverings are simpler to produce, a Reuleaux triangle or other curve of constant width would also work for this purpose.
• In terms of resistance to the earth’s compression, round tubes are the most durable and material-efficient shape.
• A round manhole cover of the same width has a larger surface area than a round manhole cover of the same diameter, so casting the round manhole cover requires less material and is, therefore, less expensive.
• Manhole frames and coverings’ bearing surfaces are machined to ensure flatness and guard against being knocked loose by traffic. In addition, lathes make it considerably simpler to machine round castings.
• Spinning circular covers is unnecessary to line them up with the manhole.
• Rolling a spherical manhole cover makes moving it simpler.
• Round manhole covers are difficult to open without a specific tool since they can be easily locked in place with a quarter turn (as in nations like France). Lockable lids can be more robustly constructed to prevent being displaced.
• While casting with several sides would often stretch at its corners, allowing the grate to rock as traffic traverses it, a circular flat metal casting will typically warp in its center (concave or convex), leaving the rim flat and uniformly supported.

Other Shapes – Other manhole shapes, often squares or rectangles, are also common. For instance, manhole covers are almost always square, rectangular, or exceptionally rarely triangular in the United Kingdom but virtually never round. It is unusual to find triangular manhole covers pointing in the direction of the underlying flow in Nashua, New Hampshire. The triangles, produced by a nearby foundry, were gradually phased out starting in 2011 since they did not match current safety regulations and no manufacturer of larger triangles could be located. In Hamilton, Bermuda, some manhole covers have a triangle shape and a hinge. San Francisco also has a few triangular water main covers.

In 2011, a robotics research article proposed that robots could analyze particular manhole covers’ designs and utilize them to determine their geographic positions as a backup to GPS data.

Security and Safety

Stray voltage problems have become a significant worry for utilities in urban areas. For example, while walking her dog in New York City on January 16, 2004, Jodie S. Lane stepped on a metal manhole cover and was electrocuted. These concerns have received more attention due to these and other accidents, including technical conferences on stray voltage detection and prevention. In addition, road salt, aging, rodents biting the wires, or vehicle vibrations can all lead to insulation breakdown.

Electrical arcing can cause the insulation to catch fire, natural gas leaks, methane produced by decomposing organic matter, insulation fumes, and even gasoline flushed down the toilet. An explosion, power disruptions, and fires may result from this. With 3,369 “manhole occurrences,” including 32 explosions, registered in New York City in 2014, it is the most common place for them in the United States. Due to increased energy consumption, they were most prevalent in the summer. Despite applying road salt over the winter, Chicago reported less than ten incidents that involved no explosions.

In 2021, the Boston region had 62 “events” (down from 212 in 2018). Eversource, a local utility company, will start by replacing 38,000 maintenance hole covers in high-traffic areas in 2022 with a safer ones. The lid may raise to 4 inches (100 mm) with a rail, allowing gases to escape while preventing them from soaring into the air and causing harm to nearby structures, vehicles, or pedestrians. In addition, the coverings contain vents to allow gases to run in some locations where road salt is not a problem. The corporation is also installing monitoring technology to identify hazardous gases and fires and boosting the frequency of inspections to avoid and minimize safety issues.

Some current racing vehicles have aerodynamic designs that can generate enough vacuum to raise a manhole cover out of its depression. Manhole covers must be welded or fastened to prevent injuries during racing on city streets. The manhole cover was introduced by the ground effect of the Porsche 962 driven by Brun Motorsport during the 1990 Group C World Sportscar Championship race at Circuit Gilles Villeneuve (located in a public park in Montreal, Quebec). Brun Motorsport’s Porsche 962 was following a Porsche Courage C24. As a result, the Porsche in the rear caught fire, and the race was abruptly called due to safety concerns.

Theft

When scrap metal values are high, there is frequently an uptick in manhole cover theft.

In China, where lost manhole covers contributed to at least eight fatalities in 2004, manhole cover theft can be a severe issue. According to China’s Xinhua News Agency, about 240,000 manhole and street-drain covers were stolen in Beijing in 2004.

James Kynge characterizes the phenomenon in China Shakes the World as follows:

…during the several weeks starting in mid-February 2004, manhole covers began to vanish from roads and pavements all around the world, initially slowly but quickly gaining speed. Thieves everywhere believed that Chinese demand increased scrap metal prices to all-time highs. So as night fell, they raised the iron covers and sold them to neighborhood traders, who disassembled and loaded them aboard ships bound for China. The island nation of Taiwan, which is close to the southeast coast of China, experienced the first displacements. The next ones were in other nearby countries, like Kyrgyzstan and Mongolia. After that, thieves worked to feed China everywhere the sun went down. In Chicago, more than 150 covers vanished in a single month. In just a few days, more than a hundred disappeared during Scotland’s “great drain theft.” Unwary pedestrians fell into holes from Montreal to Gloucester to Kuala Lumpur.

In 2004, over 200 grates and covers in Newham, East London, were taken. Ten years after it was installed, an Antony Gormley-designed manhole cover was stolen.

In two months in 2004, over 10,000 manhole covers were stolen from Kolkata in India. Again, concrete covers were put in their place, but those were taken for the rebar they contained.

Numerous manhole covers were taken in March and April 2012 from Ajax, Ontario, and Niagara Falls, Ontario.

In a single day in December 2021, 30 manhole covers were reported stolen in Chatham County, Georgia.

Propelled into space

According to urban legend, a manhole cover accidentally launched from its shaft during an underground nuclear test in the 1950s at a fast enough speed to reach escape velocity. The myth is based on an actual incident during the Operation Plumbbob atomic tests when a 900 kilogram (1,984 lb) steel plate cap was launched at an unknown speed off the test shaft and captured as a blur on a single frame of film. It was never recovered, but it is likely to have burned up in the atmosphere due to friction. Before the incident, a calculation predicted a speed of six times the Earth’s escape velocity. However, it seems unlikely that the forecast was accurate.

Loading Classification

For locations with foot or vehicular traffic, the European Norm EN 124 of 1994 applies to manhole and storm drain tops with a clear aperture of up to 1 m. (covers with a clear opening over 1 m are specified in the British Standard BS9124, for example). Depending on the use, EN 124 specifies various weight classes and applies in some nations outside the European Union. The maximum weight that the lightest class A15 (cast iron) manhole cover can support is 1.5 tonnes. Usually, it would only be used for light-duty purposes in pedestrian walkways, gardens, patios, and driveways. However, in docks, airports, and other highly heavy-duty applications, the heaviest F900 class manhole cover is often employed. On the other hand, the most severe class F900 manhole cover can support up to 90 tons of weight, making it ideal for docks, airports, and other heavy-duty applications.

Conclusion

Since the 1980s, there have been several manhole covers in Japan with artistic designs. They are popular enough to support goods and events, and by 2019, Japan will likely have 12,000 different methods. These could be discovered in almost all of the country’s cities and towns. In addition, numerous manhole covers throughout Japan with Pokémon themes have also incorporated popular media franchises like Gundam and Pokémon.

Taiwan and Vietnam have used manhole covers as the subject of street art.