MIL-PRF-24755B(SH)
The purpose of the test is to assess the structural integrity and the smoke characteristics of the composite material
separating the ship's internal compartments from the air flow within the confines of the composite envelope. Gases
released to weather are also assessed as they can be reingested into the ship.
Modifications to FM4922 are as follows:
Test material. The manufacturer has the option to furnish sufficient material to assemble:
a.
Two 24-foot composite ducts incorporating at least two factory or field assembled joints (as appropriate to
the application) or
b.
Two 12-foot composite ducts incorporating at least two factory or field assembled joints along with two 12-
foot heavy-gage steel ducts (uncoated carbon steel or stainless steel) to be connected down-stream of the
composite test sections to form a standard 24-foot test section.
All of the test ducting described above (composite and supplemental steel sections, if utilized), can be provided in
the form of rectangular or circular cross-sections (depending on the envisioned application; i.e., round for fan
casings, rectangular for cabinets) that are each 6-foot and flanged for standard 24-foot test length. If rectangular
ducting cross-sections are utilized, the following nominal dimensions are commended: 12 inches by 24 inches by
nominal thickness (not to exceed 1.5 inches). If circular ducting cross-sections are utilized, the internal diameter
should not be less than 18 inches nor greater than 20 inches and the wall thickness of the test ducts should not
exceed 1.5 inches.
Test apparatus. The standard 12-inch by 12-inch by 7-inch fire pan specified in FM4922 to simulate building fire
conditions (using heptane fuel) should be enlarged to 16inches by 16 inches by 15 inches deep to more closely
simulate a shipboard engine room hydrocarbon pool fire.
FIGURE 2. Modified factory mutual fire test for composite material
(FM4922) subject to internal fire insult.
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