- Demonstrate the ability of materiel to operate in fuel-air explosive atmospheres without causing ignition, or
- Demonstrate that an explosive or burning reaction occurring within encased materiel will be contained, and will not propagate outside the test item.
This method applies to all materiel designed for use in the vicinity of fuel-air explosive atmospheres associated with aircraft, automotive, and marine fuels at or above sea level. Procedure II specifically relates to atmospheres in a space in which flammable fluids or vapors exist, or can exist, either continuously or intermittently (e.g., in fuel tanks or within fuel systems). The Method provides for two Procedures:
I – The item under test operating in an explosive atmosphere without igniting the air/fuel mixture environment.
II – Determine the ability of the test item to contain an explosion or flame that is the result of an internal malfunction.
The test involves placing the item under test inside a chamber that is filled with an explosive mixture of air and n-hexane. N-hexane is specified because its ignition properties in flammable atmospheres are equal to or more sensitive than the similar properties of 100/130-octane aviation gasoline, JP-4 and JP-8 jet engine fuel. The chamber is maintained at the maximum temperature the item may experience. Also, altitude is simulated as appropriate. The energy required to ignite a fuel-air mixture increases as pressure decreases. For Procedure I, operate the item in an explosive atmosphere to determine if it will ignite the mixture. For Procedure II, introduce an explosive mixture into the test item and ignite that mixture. Assure the resulting explosion is contained inside the test item and does not ignite the explosive mixture in the chamber.