People don’t think much about manholes. They are circles in the street with a metal lid on them. You see them occasionally open with caution tape and traffic cones around them, warning motorists and pedestrians to stay away, but beyond that, they pretty much blend into the street…until there is an explosion and the cover blows off. Ventilation is very important in any plumbing system or enclosed space and proper manhole ventiliation is a crucial safety issue.
Providing proper ventilation is one of the fundamental parts of good plumbing design, whether the plumbing is in a home or under a city street. Ventilation keeps gasses like methane and ammonia from entering spaces where people go, and this is true of manholes and municipal tunnels as well. It is very important to test for oxygen levels and dangerous gasses before descending into a manhole.
When workers enter a manhole, they must wear different types of protective gear to keep them safe from different contaminants. This equipment can include hazmat suits, respirators, oxygen tanks and safety helmets. Before anyone goes into a manhole, the crew should have ventilation equipment running to provide a continuous supply of fresh air. There should be workers at street level to monitor the equipment and go in and rescue their coworkers if necessary. A particular problem with working below the street is static electricity build-up. There are special suits that reduce the amount of static and the danger from fire.
Fans and Blowers
Government regulations require enclosed spaces to be ventilated while people are working in there. Different types of fans and blowers are used to circulate the air and make sure the oxygen level is high enough and levels of dangerous gasses are within regulatory limits. Manhole ventilation fans are made to run safely in an enclosed space and not produce static which could ignite gasses.
Working underground can be dangerous and safety precautions for ventilation are important. Think about this the next time you drive over a manhole cover.