Downloaded from https://www.everyspec.com MIL-STD-81OD 19 July 1983 a. Required information to determine fuel weight: (1) Chamber.air temperature during the test. .(2) Fuel temperature.“ (3) Specific gravity of ri-hexane(see figure 511.2-1). (4) Test altitude: e.g., 6100 meters (20,000 feet). Atmospheric pressure in pascals: 46.6 kFa (6.76 psia). (5) Net.volume of the test chamber: free volume less test item displacement expressed in liters or cubic feet. b. Calculation of the“:.volume of liquid n-hexane fuel for each test altitude: 1) In metric units: . Volume of 95 percent n-hexane (ml) . ., (396x 10-6) c gravity, n-hexane (2) In English units:
Volume of 95”percent n-hexane (ml) = rcha ber cn-essure(D specificmgravity of n-hexane I-3.2.5 .ECfeotof hu~dltv on fla~~. . Humidity is always present in an explosive atmosphere test. The effect of humidity upon the fuel-air mixture percent composition need not be considered in the teat if the ambient air dewpoint is 10° C (50° F) or less because this concentration of water vapor only increases the n-hexane fuel concentration from 3.82 percent to 3.85 percent of the test atmosphere.
If the atmospheric pressure is cycled from 1525.meters (5000 ft.) above the test leVel to 1525 meters below (a 34-perCent change.in pressure), the volume of n-hexane will decrease from 4.61 percent to 3.08 percent. This decrease will compensate for the fuel enrichment effect that results from water vapor dilution of the test air supply. I-3.2.6 ~. The maximum altitude at which the test item will be,exposed to fuel vapors during operation shall be the maximum test altitude, unless otherwise specified. If the test facility is not at sea level and the test,is for shipboard equipment, the test chamber shall be pressurized to simulatesea level, unless otherwise specified.
MRTHOD 511.2 19 July 1983 511.2-3