Downloaded from https://www.everyspec.com MIL-STD-81OC Step I - The test chamber shall be sealed and the ambient tempera- ture within shall be raised to *3,° C(160” f5°F), or to the maximum temperature to which the test item is designed to operate if lower than 71“C (160”F)., The temperature of the test item and the chamber walls shall be permittedto rise to within II° C (20°F) of that of the chamber ambient air, prior to introductionof,the explosive mixture. Step2 - The internal test chamber pressure shall be,reduced sufficientlyto simulate”an altitude approximately10,000 feet above the desired test altitude.
The weight of fuel necessary to produce an air-vapor ratio of 13-to-1 at the desired test altitude shall be determined from considera- tion of chamber volume, fuel temperature and specific gravity, chamber air”and wall temperature, test altitude, etc. If the performance of this test will expose the equipment to an altitude in excess of its specified maxi- mum operating or honoperating altitude the next lower simulated test altitude shall be selected.
The testing of ground equipment (equipmentfor operationaluse on the ground or aboard ship) shall be limited to an increase in the chamber altitude to 15,000 feet with the equipment nonoperatingand the weight of fuel shall be admitted to the chamber while the altitude is being reduced to 10,000 feet (see.2.l.1). A time of 3 +1 minutes shall be allowed for introductionand vaporizati~n of the fuel. Air shal1 be admitted into the chamber until a simulated altitude of 5,000 feet above the test altitude is attained. Step 3 Operation of the test item shall at this time be co~enced,. all making and breaking electrical contacts being actuated.
If high temperature components are present, a warmup time of 15 minutes shall be permitted. If no explosion results, air shall be admitted into,the chamber so as to steadily reduce the altitude down past the desired test altit,udetO : an elevation 5,000 feet below that altitude. If necessary, conduct tests to simulated sea”level pressure by pressur-. izing chamber. Tests shall not be conducted below sea level. The operation of the test item shall be coritinuous throughout this period of altittidereduction and all making and breaking electrical contacts shall be operated as frequently as deemed practicable.
Ground equipment shall be energized at 15,000 feet and the sources of igniting I energy operated until the chamber altitudeis reduced to sea level. METHOD 511.1 511.1-4