Significant emphasis has been placed on aircraft fuel tank safety following the TWA Flight 800 accident in July 1996. Upon investigation, the National Transportation Safety Board (NTSB) determined that the explosion of the center wing tank (CWT) resulted most likely from ignition of the flammable fuel/air mixture. The growing concern of aircraft fuel tank safety has taken an added dimension in the post 9/11 world where both commercial and military aircrafts are vulnerable to terrorist attacks utilizing MANPADS (MAN-Portable Air Defense Systems), explosives in shoe/socks, and small arms fire. Fuel tanks also need protection from explosions caused by ballistic impact, lightning, and other sources of ignition. In Phase I, InnoSense LLC has demonstrated the feasibility of an all-optical oxygen sensor capable of detecting oxygen at 40,000 feet elevation down to the ambient level. This Phase II proposal discusses how InnoSense LLC would develop a prototype and perform field testing. The project team possesses seventy person-years of optical sensor related hardware and software expertise. InnoSense has attracted $300,000 in Phase III follow-on funding for further engineering. Innosense will deliver the prototype to NASA, complete with software, manuals, and schematics.