We’re wanting to convert an old mechanics grease pit into a storm shelter. What would be the best way to do. We were thinking concrete for a slab and a wooden door for entrance. What is the best way to do the concrete slab. Thickness? Best way to hold it up until dried...etc. Thanks

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    I recommend that you hire a professional engineer who specializes in such structures to advise you on the proper way to suspend a concrete roof over your pit both during construction and permanently. If you make an error you could end up creating a death trap vs. a shelter. – jwh20 Apr 21 '20 at 15:53
  • I agree with jwh20, too many details and particulars along with an elevated risk, go professional and hire a structural engineer – Ack Apr 21 '20 at 16:07
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    I will bet that you'll find it a lot less expensive AND a lot more pleasant to shelter in something new, rather than a fairly shallow pit with decades of petroleum drips soaked into it. Remediating the petroleum to a point where you could actually stay in the shelter through a storm will be a major expense, I expect. Dig a hole, drop in a precast concrete shelter, bury it; is very straightforward by comparison. – Ecnerwal Apr 21 '20 at 16:58
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    @Ecnerwal is right -- precast septic tanks may be large enough for your purpose. If you do go ahead with using the grease pit, I would say cover most of the opening with something like 4X10 lumber and bolt the lumber with long ground spikes or similar. You don't need a fullsize door - just a "hatchway" which could even be 1/4" steel. – Carl Witthoft Apr 21 '20 at 18:48

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