Everyone knows a few things that make manholes dangerous: alligators, phantom of the opera, and C.H.U.D.s, to name a few. You’re on your own when it comes to those things, but I can offer advice on other hazardous stuff that can happen in and around a manhole. Thankfully, the right preparation can guarantee safety within this confined space.
It is necessary to have a certificate that validates the safety of the confined space before entering a manhole. Don’t just test it yourself by tossing a match down there to see if it is full of poison gas. (Check for gas the right way with a 4-gas monitor.) Generally, a work site will have a single person who is known as a “competent person,” one who has the right credentials and experience to outline the necessary safety precautions, which are then implemented by the person running the work site. These precautions include the site itself and any equipment needed for a descent.
Safety comes first both under and above ground. Thankfully, the right precautions can guarantee safe passage. Gas valves have to be closed, generators cannot emit fumes into the hole, and any sludge in the pipe has to be removed, since it can harbor toxic gases. Also, it is essential to keep the air in the pipe fresh. Make sure that plenty of blowers are filling the confined space with clean air and that there are ample power outlets for this equipment.
Beyond the mechanical stuff, there is a human side to ensuring safety. One’s fellow workers are key to a safe job. Co-workers are responsible for erecting fencing and posting warning signs, so that an errant bicyclist doesn’t end up taking an unexpected detour through the work site. Any time a person descends, there should be plenty of co-workers above ground, in case the person descending runs into trouble of any kind.
Safety is a communal process, even though only one person may actually be in the manhole. Remembering that premise can guarantee that the whole worksite remains safe. If you follow these simple guidelines, the only thing you will have to worry about are the alligators. (For more information check out OSHA's guide to Safety in Confined Space.)