Downloaded from https://www.everyspec.com MIL-STD-81OC 10 March 1975 METHOD 518.1 TF24PERATURE-HUMI DITY-ALTITUDE 1. PURPOSE. The temperature-humidity-altitudetest is conducted to determine the effects of cycling between low temperature/lowpressure and high tempera- ture/high humidity as may be obtained in service by flying equipment between extreme environments. 2. APPARATUS. Temperature-humidity-altitude chamber. No rust or corrosive contaminants shall be imposed on the test item by the test facility. 3. PROCEDURE I Step 1 - Prepare the test item in accordance with General Requirements, 3.2. Step 2 - Reduce the chamber temperature to -54° C (-65”F) within 2 hours.
Step 3 - Reduce the chamber pressure at a rate of 1,000 to 1,500 ft/min to 50,000 feet altitude while maintaining the specified -54° C (-65”F) temperature. The time from the start to the completion of step 3 shall be 2-1/2 hours. Step 4 - Within 30 minutes, raise the chamber pressure to standard ambient pressure, return the chamber temperature to standard ambient temperature,and then, raise the chamber humidity to 95 percent RH. Step 5 - Maintain temperature and humidity conditions for 2-1/2 hours. Step 6 - During the next 30 minutes, increase the temperature to 65° C (149”F) and maintain humidity at 95 percent RH. Step 7 - Maintain temperature and humidity conditions of step 6 for 6 hours.
Step 8 - During the next 8 hours, reduce the chamber temperature at a uniform rate to standard ambient temperaturewhile maintaining humidity at 95 percent RH. Step 9 - Maintain standard ambient temperature at 95 percent RH humidity for 2 hours. NOTE: Steps 2 through 9 constitute one cycle as shown on figure 518.1-1. 518.1-1 METHOD 518.1 10 March 1975