Manhole Covers

I am doing some research on how to improve on my interview skills for another upcoming round of interviews, next week and came across this: Why is a manhole cover round? I found it an intriguing interview question and my first response was to think, why is a manhole cover round? The best that I could come up with was that it must be a health and safety thing of some sort. Thinking about the shape, a round cover wouldn’t be able to fall through a round hole, but a square cover, if held diagonally would and that’s the best I could come up with.

Talking to Rem on Skype later in the day I asked, why is a manhole cover round? He thought about it for a second and answered, so that the Teenage Mutant Ninja Turtles who lives in the sewers can fit through easily with their turtle shells. Brilliant.

Chris came home from work and my first question, why is a manhole cover round? Mmmm, said Chris, thinking, uhmm…. then gave me that look he gives me of I don’t want to disagree with you because that’s never a good idea, but I can’t see any other way out of it. They’re not, he finally says. Manhole covers are square in the UK. And ever since, whenever we’re out driving and drive over one, Chris says ‘square’.

I loved asking the question and was pleasantly surprised by the answers.

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  1. As you probably know, most (if not all) sewer pipes are round themselfs because this shape has the most resistance to the compressing force of the ground around it.

    So instead of creating a square end on a round pipe it is natural that they just made the covers round aswell. ;)

    At least that is my best guess :P

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