Shanghai’s magnificent cityscape is breathtaking. Yet， it would be known for a whole other scene if its pavement was transparent： Underneath the streets is what’s known as the city’s “intestinal tract”： an interwoven municipal sewer system. The streets sometimes get flooded with sewage when any part of the system gets stuck.
　　Therefore， a group of “subterranean doctors” treat the underground “intestinal tract” when it suffers indigestion， something most people hope to never witness.
　　Hailed as underground “frogmen”in cities， such heroes usually wear heavy， airtight diving suits to unclog the narrow， dark sewage pipes.


　　Working in such conditions is certainly a challenge even before you factor in the weight and rigidity of their suits， the lightest of which weighs five kilograms， and the heaviest， for the deepest tasks， 30 kilograms. To reach the bottom of a pipe， they are weighted down with 15 kilograms of lead in front and 15 on their backs.
　　Under the city’s pump house is a sludge sedimentation basin for filtering sewage and other waste out of the wa- ter. One major task of the frogmen is to clear the drainage exit， which requires gas masks because of the high content of hydrogen sulfide in the basin. They cannot work continuously for more than 20 minutes.


　　Usually working alone， frogmen must be psychologically strong and remain calm under pressure. It’s important to keep a clear head when stuck in the pipes， dealing with a tangled air tube， enduring a leaky suit or battling a malfunctioning air valve.
　　The municipal government of Shanghai has always strictly administered diving operations in its underground network. As well as certifying the training of frogmen， involved companies must pass annual examinations and verification. No mission can start without written permission.
　　Today， 130 frogmen in Shanghai are qualified to tackle such jobs.