30 CFR § 27.41
Test to determine resistance to moisture.
Components, subassemblies, or assemblies, the normal functioning of which
might be affected by moisture, shall be tested in atmospheres of high
relative humidity (80 percent or more at 65°-75°F.) for continuous operating
and idle periods of 4 hours each. The component or subassembly or assembly
shall function normally after being subjected to those tests.