1.1 Purpose
The explosive atmosphere test is performed to either:
- a. Demonstrate the ability of materiel to operate in fuel-air explosive atmospheres without causing ignition.
- b. Demonstrate that an explosive or burning reaction occurring within encased materiel will be contained, and will not propagate outside the test item.
1.2 Application
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. The flammable/explosive vapors may originate either from the equipment itself or from an external source. 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).
NOTE: Materiel tested to Procedure II is designed such that ignition of an explosive mixture is contained within the materiel without igniting the surrounding explosive atmosphere and, during normal operation, or as a result of any fault, the temperature of any external surface will not rise to a level capable of causing ignition (including hermetically-sealed materiel).
1.3 Limitations
- a. These procedures use an explosive fuel-air mixture that has a relatively low flash point that may not be representative of some actual fuel-air or aerosol (such as suspended dust) mixtures.
- b. The explosive atmosphere test is a conservative test. If the test item does not ignite the test fuel-air mixture, there is a low probability that the materiel will ignite prevailing fuel vapor mixtures in service. Conversely, the ignition of the test fuel-air mixture by the test item does not mean the materiel will always ignite fuel vapors that occur in actual use.
- c. These procedures are not appropriate for test altitudes above approximately 16 km where the lack of oxygen inhibits ignition.
- d. While the Method is not intended to test for high surface temperatures, it does not preclude this possibility (this Method is intended for spark ignition).