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View Full Version : what size of a man can fit into a manhole?


goemon
09-01-2009, 11:04 PM
whenever i see manholes i always think they are too small for anyone to enter but i know people are supposed to be able to gain entry. what are the size guidelines required of people to get a job that requires manhole entry?

Snarky_Kong
09-01-2009, 11:14 PM
whenever i see manholes i always think they are too small for anyone to enter but i know people are supposed to be able to gain entry. what are the size guidelines required of people to get a job that requires manhole entry?

I'd think anybody under 250+ lbs could get in pretty easily. They're not supposed to be cozy, it's just an access point.

Jragon
09-01-2009, 11:19 PM
The smallest manhole size I'm finding purely through a cursory search is 1000mm (which I assume is diameter since it says width), or about 33 and 1/3 inches.. Even when I was 195 pounds my waist size never exceeded 36 inches (granted I do have a slightly smaller than average frame). I'd imagine that anyone who isn't about, oh, let's go with Snarky Kong's 250+ pounds could fit, though it would probably get rather tight near the upper ends of that (230+ probably). And note that was the absolute smallest I saw, I'd imagine a lot of cities use the 1200mm/47in or 1500mm/59in sizes I also saw.

Civil Guy
09-01-2009, 11:27 PM
They range in size (the manhole covers as well as the people) from 24" diameter (61 cm) on up to, say, 48" diameter (122 cm). Generally, the manholes underneath flare out some. The covers are the small part because there's no call to put a bigger hole in the pavement than necessary.

No point, though, in a manhole too small for workers to get into.

The smaller manhole covers would be used for shallow manholes, such as those as for 'catch basins', the drainage boxes you can see in curb areas.

Johnny L.A.
09-01-2009, 11:29 PM
1000 mm = 39.37 inches. So the circumference would be 123.68 inches. That's a pretty hefty waist/shoulder size!

What amazes me are the WWII newsreels, where sailors are going down hatches that seem impossibly small. During/after the attack on Pearl Harbor, some sailors escaped through portholes. (Granted, many who did lost some skin.) It's amazing what people can get through if they have to.

KneadToKnow
09-01-2009, 11:33 PM
I currently weigh ca. 310. I've never seen a manhole that looked like it would have been a particularly tight squeeze.

Wait, what? ;)

I had a friend in grad school whose weight tended toward 400, and he might have had some trouble with the smaller ones.

Zsofia
09-01-2009, 11:34 PM
Witness a baby being born - yes, the skull deforms, but the shoulders don't and they fit through.

Johnny L.A.
09-01-2009, 11:37 PM
Witness a baby being born

Only if I get to film it, have props, and can add special effects.

SuperNelson
09-01-2009, 11:38 PM
The smallest manhole size I'm finding purely through a cursory search is 1000mm (which I assume is diameter since it says width), or about 33 and 1/3 inches.. Even when I was 195 pounds my waist size never exceeded 36 inches (granted I do have a slightly smaller than average frame). I'd imagine that anyone who isn't about, oh, let's go with Snarky Kong's 250+ pounds could fit, though it would probably get rather tight near the upper ends of that (230+ probably). And note that was the absolute smallest I saw, I'd imagine a lot of cities use the 1200mm/47in or 1500mm/59in sizes I also saw.And remember - waist size is roughly circumference, not diameter. A 33" diameter manhole would fit a waistline approaching 103". Granted, perfectly circular waistlines are only found in Weebles, but that's still one big maintenance worker.

Jragon
09-01-2009, 11:50 PM
:smack:

Right, I forgot waist sizes are circumference (i'm not sure what I thought they were, clearly not diameter, secret forbidden magic I guess). Yeah, that broadens things up even more than I thought.

boytyperanma
09-02-2009, 02:31 AM
As other have mentioned they vary in size. Many of them don't have enough room below from someone to fit in in the first place its only an access where the guys work can from the top.

I'm a big guy 6'1" 250lbs. I regularly go into manholes. I've only once had an issue where I could not physical fit into one. It was access to an under basement cistern system. It was never intended for people to go through. The access was not wide enough for my shoulders to pass. We simply enlisted child labor, smallish 14y old son of a friend.

Most commonly for me is working in well pits. Most of them are 6ft deep and 3 feet in diameter. Some have a full size cement cover others have a manhole cover. You get very skilled at learning how to position in odd ways to be able to spin wrenched as needed.

09-02-2009, 03:42 AM
The covers are the small part because there's no call to put a bigger hole in the pavement than necessary.

No point, though, in a manhole too small for workers to get into.Or too small for equipment. The ones used for electrical & communications in particular, frequently have equipment underground. You need to be able to get replacements or added hardware through that access hole, too.

Uncertain
09-02-2009, 08:25 AM
Well, with sufficient lube and lots of patience, all but the.... Oh, I see. Never mind.

NinetyWt
09-02-2009, 09:11 AM
ISTR, when we had a design project for a prison once, that no opening leaving the prison could be larger than a certain diameter - I think it was 10 inches. Supposedly, a normal sized-man could escape through an 18" hole. Remember that move where the guy escaped through the sewer pipe?

muldoonthief
09-02-2009, 11:05 AM
Witness a baby being born - yes, the skull deforms, but the shoulders don't and they fit through.

True, but you rarely see maintenance workers entering manholes head first.

BetsQ
09-02-2009, 11:12 AM
Check out google image search results for "cu chi tunnels". People can squeeze into surprisingly small holes.

Thin Ice
09-02-2009, 12:17 PM
Do manholes nowadays have built in rungs to climb in and out? Back in the early '70s I was on a survey party and every once in a while we would have a job that required going into one. We had to use a ladder which narrowed the opening considerably, meaning I didn't have to go underground because I was, and am, pretty rotund.

robby
09-02-2009, 01:07 PM
Do manholes nowadays have built in rungs to climb in and out? Back in the early '70s I was on a survey party and every once in a while we would have a job that required going into one. We had to use a ladder which narrowed the opening considerably, meaning I didn't have to go underground because I was, and am, pretty rotund.Yes, manholes generally have epoxy-coated steel ladder rungs in them.

Manholes are also considered to be "confined-space" areas, so in accordance with OSHA regulations, workers have to have a harness and retrieval device, continuous atmospheric monitoring, and a portable ventilation system.

Duckster
09-02-2009, 01:58 PM
True, but you rarely see maintenance workers entering manholes head first.

But they exit head first.

gigi
09-02-2009, 01:59 PM
True, but you rarely see maintenance workers entering manholes head first.

What goes down must come up.

However, maintenance workers' bones tend to be less smushable than a baby's.

Plynck
09-02-2009, 02:57 PM
Yes, manholes generally have epoxy-coated steel ladder rungs in them.

Manholes are also considered to be "confined-space" areas, so in accordance with OSHA regulations, workers have to have a harness and retrieval device, continuous atmospheric monitoring, and a portable ventilation system.Once again, my coming late to the party consists mostly of me saying "what robby said". :)

Not so long ago, most cities and towns wanted 24" diameter manhole covers because one person could open it unaided. I have done so myself on a number of occasions. However, as robby said, manholes are considered to be a confined space, so inspections are no longer a one-man operation. (This used to be true only of sanitary sewer manholes, but now applies to storm drainage manholes, and electrical/telephone manholes as well). As a result, many towns are now requiring 30" manhole covers to allow personal breathing apparatus and safety equipment.

A brief and abbreviated description: A manhole is typically located to allow access to the utility it serves. This might be where a pipe makes a bend, where several pipes come together, or after the pipe has continued without interruption for a long distance. They are described as "eccentric". This means that the top section and manhole covers are not centered on the barrel sections below, but are offset to allow a continuous wall up to the surface. The manhole rungs are then mounted on that wall from top to bottom. And as the old logic question goes, why are the covers always round? They are round so that they can't accidentally be dropped through the frame and into the structure.

Catch basins, by contrast, are usually "concentric", with the top section and grate centered over the barrel section, and typically have no rungs. Catch basin grates can be square or rectangular, so if not careful then can be dropped through the diagonal of the frame.

I used to work with an engineer who was extremely circumferentially challenged, and he never had a problem getting into a manhole to inspect it.

gazpacho
09-02-2009, 03:11 PM
Witness a baby being born - yes, the skull deforms, but the shoulders don't and they fit through.It is relatively common for babies to break their collar bones when being born.

Polycarp
09-02-2009, 03:34 PM
True, but you rarely see maintenance workers entering manholes head first.

At least not the ones with non-deformed skulls! :)

CutterJohn
09-02-2009, 09:33 PM
In the navy, large deck hatches commonly have a small manhole in the center, which are 18" generally(or was it 20"). Either way, it was a tight fit, but even the larger guys I worked with could make it through them with a bit of maneuvering.

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