Downloaded from https://www.everyspec.com 2–5. Basic climatic design type. Four daily cycles represent conditions that may be found in areas where the basic climatic design type prevails. Two of these cycles represent high humidity conditions and two represent the extreme temperatures of the basic set of design values. a. High humidity daily cycles. (1) Location. Basic high humidity conditions are found most often in tropical areas, although they occur briefly or seasonally in the midlatitudes. One of the two high humidity cycles (constant high humidity) represents conditions in the heavily forested areas where nearly constant conditions may prevail during rainy and wet seasons.
The other daily cycle (variable high humidity) represents conditions found in the open in tropical areas. In the first cycle, exposed materiel is likely to be constantly wet or damp for many days at a time. In the second cycle, exposed items are subject to alternate wetting and drying. Both conditions promote severe deterioration in materiel. The one that is most important, as shown below, depends on the nature of the equipment involved.
Table 1–1 Materials and High Humidity Deterioration Type Material Type of Site with the Highest Deterioration Rates Elastomers Open Polymers Open Textiles Forest Metals Coastal swamp (mangrove) and forest (2) Temperature, humidity, solar radiation (constant high humidity cycle). (a) Operational conditions. Relative humidity above 95 percent in association with a nearly constant temperature at 75 ° F (24 ° C) persists for periods of several days (table 2-4). (b) Storage and transit conditions. Relative humidity above 95 percent in association with nearly constant 80 ° F (27 ° C) temperature occurs for periods of a day or more. 11 AR 70–38 • 15 September 1979