Jim-It sounds like a "grill" of heavy guage wire mesh of an inch or so in
diameter, similar to what Adrian Pearce mentions in his post, was fabricated
and installed around a decade ago for some shafts at the Keane Wonder Mine in
Death Valley National Park in California. The 'weave' is such that small
children can not pass through, but bats that may now inhabit the shafts, can.
The mesh or grid is secured so that a small truck or passenger vehicle, if
someone was foolish or unlucky enough to try it could be supported on the grid.
You might be able to get more information, including architects and engineers
specifications, if you want to look this far afield from:
Death Valley National Park
P.O. Box 579
Death Valley, CA 92328-0579
Telephones:
(760) 786-2331 Voice
Hope this is of interest.-Mark
Mark Henderson
Ely, Nevada USA
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