Downloaded from https://www.everyspec.com MIL-STD-81OC 10 March 1975 MSTHOD 511.1 EXPLOSIVE ATMOSPHERE 1. PURPOSE. The explosive atmosphere test is conducted to determine the abil~equipment to operate in the presence of an explosive atmosphere without creating an explosion or to contain an explosion occurring inside the equipment. Since equipments operate in ever changing potentially explo- sive atmospheres, the equipments, when being laboratory tested, must operate in the presence of the optimum fuel-air mixture which requires the least amount of energy for ignition. The equipment igniting energy may be produced electrically, thermally, or chemically. 1.1 Procedure 1.
This procedure is intended for determining the explosion producing characteristicsof equipment not hermetically sealed and not con- tained in cases designed to prevent flame and explosion propagation. Ground equipment used in or near vehicles shall also be tested in accordance with this procedure, except that the specified altitude survey need be conducted only to 15,000 feet. 1.2 Procedure II. This procedure is intended for determining the explosion and flame arresting characteristicsof equipment cases designed for that purpose. 1.3 Procedure II1. This procedure is intended for determining the explo- sion and flame arresting characteristicsof equipment cases for shipboard application.
1.4 Procedure IV. This procedure is intended for determining the flame and explosion arresting characteristicsof equipment containing hotspots in excess of 143° C (290”F). 2. APPARATUS. A chamber capable of providing and verifying the explosion- proof test conditions. MIL-c-9435 describes one type of chamber that may be used. 2.1 Fuel. Unless otherwise specified, the fuel used shall be gasoline, grade 100/130 conforming to MIL-G-5572 or a 1.05 stoichiometric mixture of propane (C3H8) and air within the following limits: propane 3.85 to 4.25 percent by volume and air 96.15 to 95.75 percent by volume. 2.1.1 Calculation of fuel-air-vaporratio.
As an illustrationof the proce- dure for calculating the weight of 100/130 octane gasoline required to produce the desired 13-to-l air-vapor ratio, the following sample problem is presented: 511.1-1 METHOD 511.1 10 March 1975