A Tunable Diode Laser Absorption Diagnostic for Studying the Fire Suppression Mechanism of Aqueous High Expansion Foams

Using direct-tunable diode laser absorption spectroscopy, we obtained simultaneous oxygen, water vapor, and temperature measurements in situ during aqueous high expansion foam-suppressed fires in a foam-adapted cup burner apparatus. Foams with expansion ratios ranging from 55:1 to 129:1 were delivered at various rates; measurements were obtained 5.5 cm above and 1.5 cm outside the cup burner exit. By monitoring water vapor as foam advances through the cup burner chimney with and without the flame present, we are able to quantify evaporation due to the presence of the thermal and radiating field. We are also able to measure the impact on the oxygen concentration resulting from flame consumption of oxygen versus release of oxygen from evaporating foam bubbles. By analyzing video captured during each foam injection event, foam velocities during fire suppression and in the absence of the flame were measured.