Explosive Atmosphere

This test is performed to demonstrate the ability of equipment to operate in flammable atmospheres without causing an explosion, or to prove that a flammable reaction occurring within an encased equipment will be contained and will not propagate outside the test item.
Low levels of energy discharge in electrical arc from devices as simple as pocket transistor radios can ignite mixtures of fuel vapor and air. A "hot spot" on the surface of a hermetically sealed, apparently inert equipment case, can ignite fuel vapor and air mixtures. Fuel vapors in compartments can be ignited by a low energy discharge like a spark from a shorted flashlight cell, switch contacts, etc.
Variables
Temperature	Altitude
Test item configuration	Fuel and vapor mixture
Applicability
This testing is applicable to military hardware, commercial aircraft equipment, automotive components, operating room equipment and European safety standards.
Methods of Test
Safe Operation
This procedure is applicable to all types of sealed and unsealed equipment. This test evaluates the ability of the test item to be operated in a fuel vapor-laden environment without igniting the environment.
Containment
This procedure is used to determine the ability of the test item’s case or other enclosure to contain an explosion or flame that is a result of an ignition internal to the equipment.
Test at Altitude
The fuel normally recommended for explosive atmosphere testing of aircraft equipment is hydrocarbon n-hexane because its ignition properties, for flammable atmosphere testing, is equal to or better than the similar properties of both 100/130 octane aviation gasoline and Jet A fuel.
The fuel vapor mixture is heated to the highest ambient air temperature at which the test item is required to operate during actual deployment. Heating the ambient air to this temperature gives the fuel vapor mixture its greatest likelihood for ignition.
The altitude at which the test item will be exposed to fuel vapors, during operation, will normally be the maximum test altitude.
Test at Sea Level
Another technique for testing aircraft components is to measure the temperature of the hottest components. If they are less than the ignition temperature of the fuel, the product passes the test.
Testing for intrinsically safe products is normaly performed with propane or hydrogen gas.

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