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Abstract

A composite sandwich panel structure having first and second honeycomb core layers and fire barrier membranes separating the honeycomb core layers as well as forming facing skins provides protection from burn-through after 15 minutes of subjection to a 2000.degree. F. front side flame impingement at 10.5 btu/m.sup.2 heat flux density, with a 110.degree. F. average off-surface temperature 12' off of the backside of the panel. The facing skins on the outside of the honeycomb core layers are preferably formed by a layer of vermiculite film together with a layer phenolic prepreg. The center septum layer separating the first and second honeycomb core layers can be an inorganic fiber membrane, with a layer of phenolic prepreg on both sides thereof, and/or a layer of vermiculite film or other suitable materials providing a fire barrier. The honeycomb core layers are preferably made of a nylon paper honeycomb having a coating that itself forms a fire barrier, such as a coating of 80-96% sodium silicate, 1-4% vermiculite HTS and 2-15% H.sub.2 O based phenolic resin.

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First Claim