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Compressed air foam (CAF) and compressed nitrogen foam (CNF) have been widely used for storage tank fire suppression, benefiting from their highly effective extinguishing performance. Mass loss rate is an important parameter to evaluate the stability of foam and an important factor to influence the suppression efficiency of foam. In this work, mass loss mechanisms including drainage and evaporation of two types of foams under a fixed radiation source were experimentally studied to reflect the foam fire suppression efficiency. It was observed that the foam drain rate is directly proportional to the foam mass, with a slight relation to the irradiance when irradiance is lower than 20 kW/m2. Once the irradiance reaches 30 kW/m2, the drain rate increases significantly. For evaporation, as expected from the established theoretical model, the evaporation rate shows a positive relationship with the irradiance level. However, there is no relationship between foam evaporation rate and the initial foam thickness. Through the experimentally measured evaporation rate, the average foam absorptivity is calculated to be approximately 0.63 ± 0.07 for both foams at an expansion ratio (ER) of 10. A comparative analysis of mass loss characteristics in the two types of foam was also undertaken. It was found that the two types of foam have distinct drain rates due to their different foam stability caused by the different expanded gas properties. However, they have a similar evaporation rate. In addition, the foam destruction rate and time to ignite the underlying fuel were measured, and a linear relationship between ignition time and initial foam height was found with a slope of 1.7 ± 0.2. The results demonstrate that CNF has a better fire suppression efficiency, which can be attributed to the better stability of the foam and the nitrogen released by broken bubbles, which inhibits ignition. The work presented here reveals the different functional mechanisms of compressed air/nitrogen foam and presents useful information that could enhance our understanding of the fire suppression effects of fire extinguishing foam. [ABSTRACT FROM AUTHOR]

Fire-fighting foam has been widely used as a kind of efficient clean liquid fire extinguishing agent. The spreading of foam is an important index to evaluate the fire suppression performance of foam, which determines whether the foam can quickly cover the whole pool surface in the fire extinguishment process, effectively inhibit evaporation and isolate oxygen. In this work, the foam spreading experiments on the surface of fuel layer with different thicknesses (3–15 mm) were carried out. The results indicate that the decrease of the thickness of the fuel layer could slow down the foam spreading. There is a saturation thickness, beyond which the fuel layer thickness no longer affects foam spreading, because the flow in the fuel layer is transformed from Couette flow to boundary layer flow. Meanwhile, both the increase in the foam flow rate and decrease in the expansion ratio reduce the effect of fuel layer thickness on foam spreading. And at a foam flow rate of 14 L/min or expansion ratio of 5.5, the foam spreading is scarcely affected by the thickness of the fuel. Furthermore, it was found that the foam with smaller expansion ratio spreads faster than that of the lager expansion ratio due to larger pressure gradient at the same foam thickness. The work presented here enhances the understanding of the spread of foam over fuel. [ABSTRACT FROM AUTHOR]

A multi-component compressed air foam system (MCAFS) was developed with newly prepared multi-component foaming agents. Extinguishing of wood crib and oil pool fires was performed under different conditions, such as foam concentration, mixing chamber forepart structure and working pressure. It was found that the foam concentration had sufficient effects on fire extinguishing efficiency, and an optimized concentration value exists. For instance, for diesel oil pool fires, this value is about 2.2% while it is about 4.0% for wood crib fires. The results also show that the system with a coaxial mixing chamber has greater efficiency than a T-shape. The effects of working pressure on fire extinguishing are evident in experiments, i.e., the higher the working pressure is, the more readily the fire is extinguished. [ABSTRACT FROM AUTHOR]