Comparative Measurements of TDLAS and Multi-gas Sensor to Monitor Fire Extinction Inside Small-Scale Backdraft Compartment Using CO2 and CO Concentrations

The ability of carbon dioxide gaseous species profile measurements to track the time of visual fire extinction was examined using a small-scale backdraft compartment. Carbon dioxide (CO₂) concentrations were measured using a tunable diode laser absorption spectroscopy (TDLAS) system and a multi-gas analyzer (MGA). The compartment was modified to pass laser light through a lower region of the compartment, near the burner surface, and in the over-fire region where the flame was well-mixed. A thermocouple probe and gas sampling lines for extracted gas samples to the MGA system were installed close to the two laser paths. A borescope was used to visually confirm flame extinction times for nominal 37.5 kW methane fires, analyzed with ignition to fuel off times of approximately 210 s, 270 s, and 300 s. The MGA system validated carbon monoxide (CO) and CO₂ profile abilities to accurately track visual fire extinction in lower and upper positions, with roughly 2.7% and 8% error relative to visual fire extinction, respectively. The CO₂ TDLAS system demonstrated 0.7% and 1.4% error relative to visual extinction times in the lower and upper positions respectively. The ability of the TDLAS system to track visual fire extinction at a physical position away from the burner surface more accurately than the MGA system at the lower position indicates the potential of this measurement technique to monitor fire extinction in a variety of optically-inaccessible environments.