Flammable Gas Mixture Test Fixture Standardizations

Lightning strike and static electricity ignition hazard testing for aircraft typically follow one of two test methods per SAE ARP5416A. These two methods detect the presence of an ignition hazard through either (1) the combustion of a flammable gas mixture ignitable by a 200 microJoule (µJ) voltage arc or (2) light emission greater than that of a 200 µJ voltage arc. The instrumentation and test conditions of the voltage arc source is not fully constrained by industry standards which could lead to overly conservative or erroneous results when performing ignition hazard testing and thus cause costlier or ineffective remediations and designs for EME protection. Understanding the sensitivities of the two test methods to different parameters that affect the optical and incendive properties of the arc is the main goal of this paper. Such parameters include the spacing of the electrode, varying the temporal waveform, and identifying the effects of the ambient humidity. Additionally, we provide recommendations on characterizing the voltage arc energy with temporal current and voltage measurement combined with numerical simulations and analysis of parasitic impedances. We also give potential alternative methods for verifying the ignitability of the flammable gas mixture and provide an equipment design for the flammable gas mixture test method. In order to deliver these results, two phases of testing are conducted with the aforementioned variables using the Boeing Company patented fixture, Patent Number 10,620,179 (Systems and Methods for Non-Flammable Indication of Incendivity) and Number 10,738,754 (Rapid Sample Ignition Test System). We then explore the use of the partial pressures alternative by exploring the sensitivity of the flammable gas to partial pressures. This method is discussed in greater detail in the draft of the upcoming Revision B of SAE ARP5416.