Fuel supply shut down in time to prevent explosion. Optical flameout detector designed to signal control system of facility to cut off supply of fuel into combustion chamber if flame goes out. which optical flameout detector designed burns methane in air to provide hot gases for 8-ft high-temperature test chamber. flameout detector for same combustor described in Acoustical Detection of Flameout in Combustor (LAR-14900). Fiber optic probes mounted to fuel-spray bar upstream of flame. No focusing optics used, and probes aimed across flow of gases at spot on combustion chamber wall downstream from spray bar. Arrangement enables flameout detection system to respond quickly to potential loss of flame since it detects movement of flame front away from spray bar face. Overall response time of detection system under 10 milliseconds.