Downloaded from https://www.everyspec.com MIL-STD-81OC Step 4 - If by the time the simplated altitude 5,000 feet below the t~st altitude @ of ground equipmene, no explosion has of operation of the test item, the potential explosiveness of the air-vapor mixture shall be verified by igniting a sample of the mixture with a spark gap or glow plug. At pressure altitudes of 20,000 feet or higher, the attainment of ignition at any altitude shall be sufficient evidence that the mixture was ignitable even though ignition was not obtained at some other point in the vicinity of the test altitude.
At any altitude below 20,000 feet, the mixture sample shall ignite immediately at the point within 3,000 feet of the test altitude. If the air-vapor mixture is not found to be explosive, the test shal1 be considered void and the entire procedure repeated. has been reduced to sea level in the case occurred as a result 3.1.3 Failure criteria. If the item causes explosion at any of the test altitudes, it shall be considered to have failed the test and no further trials need be attempted. 3.2 Procedure II 3.2.1 Preparation for test a. Preparation of test case or enclosure.
When necessary, the test case or enclosure shall be prepared for explosion-prooftesting by drilling and tapping openings in the case or enclosure for inlet and outlet hose connec- tions to the fuel vapor air mixture circulation system and for mounting a spark gap device. The case volume shall”not be altered by more than L5 percent by any modification to facilitate the introductionof explosive vapor. b. Hose installation. When inserting a hose from a blower, adequate pre- caution shall be taken to prevent ignition of the ambient mixture by back- fire or the release of pressure through the supply hose. c. Spark gap device.
A spark gap device for igniting the explosive mix- ture within the case or enclosure shal1 be provided. The case or enclosure may be drilled and tapped for the spark gap device or the spark gap device may be mounted internal1y. d. The case or enclosure with either the test item or a model of the test item of the same volume and configuration in position within the case Or enclosure shall be installed in the explosion chamber. METHOD 511.1 511.1-8