In Hawai'i, back in 99 or so, we had a problem down in Waikiki. The manholes were exploding.
Basically, manholes in Hawai'i are a two-stage affair. You have the top cover, which is usually 100-150 pounds of cast iron and three feet across, and then the second cover two feet below that which is actually air and water tight. This is because it's common for mild flooding to happen in Hawai'i, so things are designed accordingly.
Well, this actually made the problem more serious. When the lines overheat and start to burn, they heat up and make a lot of smoke, but use up all the oxygen in the space. But the actual problem is still on-going, so the wires keep heating up, the insulation keeps smouldering and pressure builds.
Finally, the pressure builds to the point where the secondary seal is popped, and a burst of fresh oxygen slips in. This causes a slight flash, which pops the secondary seal a little more, letting in more oxygen. Backdraft, essentially. The covers would go *fup*fup*FUP*FWUP*FWUMP!*POOMP!*
*BUH-WHOOM!*
Remember how heavy I said the primary manhole cover is? Imagine it getting launched up to the 20th floor of some of the buildings.
Now imagine the fun and excitement of it coming down.
Now imagine the pure joy of hearing the PR guy for Hawaii Electric Company telling us that exploding manholes are a "fact of life" in Hawai'i, and we should just get used to it.
Needless to say, he didn't last long in the position.
(no subject)
Date: 2006-09-21 07:35 pm (UTC)(no subject)
Date: 2006-09-22 03:39 am (UTC)It could be worse...
Date: 2006-09-22 05:41 am (UTC)Basically, manholes in Hawai'i are a two-stage affair. You have the top cover, which is usually 100-150 pounds of cast iron and three feet across, and then the second cover two feet below that which is actually air and water tight. This is because it's common for mild flooding to happen in Hawai'i, so things are designed accordingly.
Well, this actually made the problem more serious. When the lines overheat and start to burn, they heat up and make a lot of smoke, but use up all the oxygen in the space. But the actual problem is still on-going, so the wires keep heating up, the insulation keeps smouldering and pressure builds.
Finally, the pressure builds to the point where the secondary seal is popped, and a burst of fresh oxygen slips in. This causes a slight flash, which pops the secondary seal a little more, letting in more oxygen. Backdraft, essentially. The covers would go *fup*fup*FUP*FWUP*FWUMP!*POOMP!*
*BUH-WHOOM!*
Remember how heavy I said the primary manhole cover is? Imagine it getting launched up to the 20th floor of some of the buildings.
Now imagine the fun and excitement of it coming down.
Now imagine the pure joy of hearing the PR guy for Hawaii Electric Company telling us that exploding manholes are a "fact of life" in Hawai'i, and we should just get used to it.
Needless to say, he didn't last long in the position.
Re: It could be worse...
Date: 2006-09-22 01:23 pm (UTC)I see a new "iron man" sport: manhole cover catching!
(no subject)
Date: 2006-09-22 10:31 pm (UTC)(no subject)
Date: 2006-09-22 10:44 pm (UTC)Let's hear it for citizen journalism!
BTW, drop me a line in IM sometime, I have a new project planned for Lower Merion Township that you might find interesting.