Forum Discussion
DrewE
Jun 19, 2019Explorer II
One of the main reasons for propane off or not permitted in some tunnels is that propane is heavier than air, and if the tunnel is U shaped, lower in the middle than at the portals (as when going under a city or body of water, for instance), propane that leaks out or otherwise escapes tends to collect in the tunnel and stay there. Tunnels through mountains, which are usually constructed to be higher in the middle than at the portals, often don't have the same restrictions since propane naturally tends to flow out of the tunnel. The main reason for constructing the tunnel with the portals lower than the middle if that is possible, of course, is so that water won't collect in it.
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