Downloaded from https://www.everyspec.com MIL-STD-81OD.. 19 July 1983 Step 2. ,, Make provision to circulate the fuel-air mixture into the case being.tested. In the case of forced-air-cooled equipment, the cooling air must contain the proper fuel-air mixture. For equipment not using forced-air cooling it is necessary to drill the case for insertion of a hose from a blower, take adequate precautions to prevent ignition of the ambient mixture by backfire or release of pressure through the suPply hose. Any modification to facilitate.the introduction.of ignitablevapor shall not alter the case by more thin,t5%.. ,. . ,.. ., Step 3.
Provide positive means of igniting the explosive mixture within the case, The case may be,drilled or tapped for a spark gap, Or a spark SaP. may be mounted internally. Points of ignition should not be more than O.“5inch from any vent holes or flame arresting devices, and as many of such ignition sources.should be installedwithin the case as there are vent holes or flame arreating devices. Where the design of equipment makes.,thisimpractical, use as many points of i~ition aa are practical. , .,. Step 4. A thermocouple in~erted into the case and attached,to a sensitive galvanorneteroutside the test chamber may be used to detect explosions within the caae. . Step 5.
Insure that the air within the test chamber has a”water vapor dewpoint lower than 10° C (50° F)... Ste; 6. If the site atmospheric Dressure at the test location is leas than 633-mmwg, make provisions ~o pressurize the test chamber to at least 633 mmHg. Ground level pressures referred to in paragraph II-3.2 step 5 shall consist of pressures from 633 to 800 mmlig,inclusive. Step 7. Perform stepa,4 and 5 of paragraph II-2,.1. ‘,.. 11-3 ~.. ,. II-3:1.-~ I - oDera Ion in @“sive atmo~ t. ,.,.. ,“itep1. perform preparation for test.. .. . , Step 2. Seal chamber with testitem mounted ineide. Step 3. Raise the ambient temperature of air inside the chamber to that determined in paragraph 1-.3.1.3.
Wait.until temperatures of test item and test chamber inner walls come within 11° C of chamber,ambient air temperature. ., Step 4. Adjust the chamber air pressure to simu”latethe test altitude plus 1500 meters, as given in paragraph I-3.1.5. Step”5. Inject the required”quantity of n-hexane into,the test chamber, Step Circulate the,test atmosphere at least three, but not more’than , four, minutes to allow for complete vaporiz?tlon of fuel and the development of a homogeneous mixture. Step 7. Operate the teat item. Operation shall be continuous from step thru step 13. Make and break electrical contacts as frequently as reasonably possible. 7 METHOD 511.2 511.2-7 19-JUIY 1983