Photographic Spark Detection Film Sensitivity Study 2001-01-2923
Lightning testing performed on fuel tank components or structure utilizes photographic techniques or an explosion test cell to determine tendencies of the hardware to produce sparks. The photographic technique utilizes the no-light-on-film pass/fail criteria with a Polaroid camera at an f-stop of 4.7 and a film speed of 3000 ISO, or a 35 mm camera equivalent (reference 1 and 2).
There is speculation that although, per the test specifications, the requirements of the test are met if these film and camera settings are as specified, the various film types would not produce equivalent results. It is common for faster speed films to be grainier which could affect the ability of the film to detect small sparks. There are also color films which, depending on their manufacturer, can have different sensitivities to various light frequencies. The processing of the film can also affect the ability to discern small sparks.
Several test methods to evaluate the film sensitivity are employed as part of this study. Thermal spark sources representative of the types of materials typically photographed during laboratory testing, is one of the film sensitivity tests performed. These spark sources consist of Carbon Fiber Reinforced Plastic (CFRP) to CFRP, Titanium-to-Titanium, CFRP to Titanium, CFRP to Aluminum, and Aluminum to Stainless Steel. Film comparison tests were also conducted using standardized Light Emitting Diode (LED) light sources. The sources provide a constant frequency and constant intensity for comparison of the film types. The light intensity levels are similar to the lower light intensity levels of the thermal spark sources noted above. MacBeth color rendition tests were also performed using different brand films to evaluate the film sensitivity and to provide a consistent result that the film processing laboratory could use to evaluate the effect of modifications to the film development and printing process.