So Just Why *Are* Manhole Covers Round?

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In Hong Kong, I've witnessed countless square manhole covers, as well as those that consist of 2 triangular covers that make up the square shape. I am totally convinced by the logical (+ health & safety) fact that round covers could not fall into the hole, among others. Though I am not too sure giving this answer would guarantee a total success at the interview - interviewers look for your reasoning right? So simply saying I've found opinions that say so isn't gonna impress.

Try this instead: How many trees are there in England? (I was asked that yesterday)

Why does it never occur to anyone that manhole covers are round because the manholes themselves are round?

Round manhole covers can be tightened to the manhole by providing grooves or threading to it.

I think if I were asked this question in an interview my response (I'm fairly confrontational) would be to ask the interviewer, what are you REALLY looking for? Abstract thought? Logic? Problem solving?

Ive worked in and around manholes for years and in all parts of the world. I have seen square manhole covers. I have seen square manhole covers fall into holes because they are very heavy, not a little bit awkward, and have a tendency to slide, and the square shape allows for it. I have never seen a square manhole cover fall on anyone and safety is NOT a factor because noone would be working IN a manhole while someone was adjusting a manhole cover above them. Safety IS a factor when the poor schmuck had to lift the thing OUT of the manhole.

I suspect that the reasons that most if not all new manhole covers are now manufactured round are that 1-the cover will never fall into the hole 2-It can be moved fairly easily, 3-The round shape easily facilitates work being performed in the manhole with the most efficient use of space.

Maybe the best interview answer is that if 'I' were developing a manhole that i was going to be required to use on an everyday basis, and considering my work requirements and all other considerations, round manholes would be the logical choice for me. I cant say why others choose to.

The first answer that came into my mind was, "Because most modern men aren't square." Does that qualify me as logical? By the way, what the f... is a manhole cover, actually?

The shaft leading up to the manhole is round and as we all know a round shaped 'tube' is not only stronger than a square shaped 'tube' but it also uses less material to manufacture. Think about why submarines are round shaped, they have pressure all around it trying to crush it. The same principle applies to a manhole. Therefore the covers are round. Plus they have the added advantage that they will not fall into the hole like a manhole of a different shape would.

I grew up in Nashua, NH and remember manhole covers there were triangular. I was told it was because they wouldn't rattle.
(Should it be personhole cover?)
;-)

My first thought was that if the man in the manhole had to get equipment down there (wires, tools, etc.) the items would not get stuck as easily on a rounded surface. A square surface has corners that items would get caught on. Now that I'm thinking about it...boy am I missing something here!!!

When I was asked why Manhole covers are round the first thing that came into my head was because men are not square, silly but true.

This is a good question to use in an interview with a future reference desk librarian. They get questions along these lines all day!

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