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Firefighting foam has been widely used as an efficient and clean agent for extinguishing liquid fires. In this work, the flame spreading and burning of 0# diesel and n-heptane fuels were suppressed using pre discharged compressed air foam (half coverage of the pool). The foam can effectively prevent the liquid-phase-controlled flame spreading over diesel, but cannot prevent the gas-phase-controlled flame spreading of n-heptane. In the burning stage, for diesel, in the flame-foam interaction region, internal fuel flow was observed and theoretically investigated. Meanwhile, the foam layer gradually regresses as it is destroyed by the flame, with a smaller regression rate at a higher foam expansion ratio. Furthermore, the global burning rate of diesel slightly decreases compared with that of no foam discharge, but regardless of the foam expansion ratio or thickness. For n-heptane, total burning develops on the no-foam and foam areas, where the temperature increase rate of the foam-covered fuel decreases mainly depending on the initial foam mass, and the reduction of the radiation heat feedback is mainly related to the foam layer thickness. Meanwhile, foam bubbles are prone to coalescence on the n-heptane surface, which reduces the foam stability and allows it to degrade more quickly. This work helps clarify the mechanisms of foam suppression on high- and low-flash point fuel fire and serves as a guide for engineering applications.

The object of this study is the properties of compressed air foam with the use of modified additives: its drainage time and expansion ratio. The main properties of compressed air foam that affect the effectiveness of fire extinguishing are its drainage time and expansion ratio. At the same time, a number of authors have confirmed that the introduction of chemically modified additives into the composition of water fire extinguishing substances makes it possible to increase the effectiveness of fire extinguishing. The problem to be solved was to determine the influence of five modified additives (N4)2HPO4, N4H2PO4, (N4)2СO3, K2CO3 and KCl in the concentration range of 1–5 % by mass on the expansion ratio and drainage time of the compressed air foam. The results showed that the content of additives (N4)2HPO4, N4H2PO4 and (N4)2СO3 in the aqueous solution of the foaming agent does not affect its expansion ratio within the given limits. On the other hand, with K2CO3 and KCl additives, it was not possible to obtain compressed air foam with a expansion ratio of 5–20, that is, their inefficiency in compressed air foam was noted. The characteristic dependence of the effect of (N4)2HPO4, NH4H2PO4 and (N4)2СO3 additives on drainage time has been determined. The greatest drainage time is characteristic of the K≈20 generation mode. The highest recorded drainage time index was established for N4H2PO4, namely 5.45 min; for (NH4)2HPO4 the drainage time was lower by 8 %; for (N4)2СO3 the drainage time was lower by 20 %. At the same time, with the use of (N4)2HPO4, N4H2PO4 and (NH4)2СO3, it is characteristic to obtain a foam with lower drainage time compared to foam of a conventional composition. Thus, for foam with a expansion ratio of K≈20, the drainage time of foam with NH4H2PO4 is lower by 17 %, with (NH4)2HPO4 by 23 %, and with (NH4)2СO3 by 33 %. The effect of reducing the drainage time of the foam can have a decisive role in reducing its effectiveness when used for extinguishing flammable liquids due to the extinguishing mechanism but is not decisive for extinguishing solid substances. Therefore, the fire-extinguishing effectiveness of compressed air foam with modified additives during the extinguishing of solid combustible materials in comparison with the conventional CAF composition requires further study [ABSTRACT FROM AUTHOR]

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 accidents are a source of concern for electric vehicles (EV). The spread of fire caused by thermal runaway (TR) in a scenario with a high concentration of EVs can result in a serious disaster. In this study, a full-scale EV fire experiment was conducted using thermal abuse to investigate response strategies to EV fires caused by TR. The pattern of TR fires spreading in EV was also investigated. The suppression capabilities of fire blankets, water spray, and compressed air foam on EV fires in the early stages were analyzed. During the test, the temperature distributions inside and outside the vehicle were measured. The maximum temperature recorded in the passenger compartment near the roof was 919.7 °C. The length of the jet flow was estimated from the images, with the longest being approximately 2.56 m. The fire suppression test demonstrated that the fire blankets effectively extinguished flames, and the temperature inside the car gradually decreased. A water mist device can reduce temperature and put out flames. The compressed air foam effectively extinguished the fire, with an average cooling rate of −9.8 °C/s. These results provide information on EV fire response strategies.

Compressed air foam (CAF) is widely used as a high-performance extinguishing agent for liquid fuel fire. In this work, the effects of initial fuel surface temperatures (50–80 °C) on the drainage and evaporation of CAF were studied experimentally. It was found that at the same foam mass, the drain rate is positively correlated to the initial fuel surface temperature. Furthermore, the drainage and evaporation with ER = 5.5 is less affected by the fuel surface temperature than ER = 10. Then the foam height was recorded and it was observed when the temperature is above 60 °C, the foam height with ER = 10 reduces rapidly at the beginning, while only slight thermal expansion occurs in ER = 5.5. In addition, the cooling effect of the foam was studied. The fuel layer temperature variation could be divided into three stages: rapid decline, relatively stable and gradual rise, which may relate to the foam drainage. But in the rapid decline state, the drop in fuel temperature is mainly related to the heat transfer between the fuel and foam. In addition, for the foam with ER = 10, the rising stage starts earlier. This work improves the understanding of mass loss and suppression mechanisms of fire-extinguishing foams.

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Water and foam have different fire-extinguishing mechanisms. Traditional foam and compressed air foam (CAF) have different bubble structures. These differences result in different thermal characteristics, which affect the extinguishing abilities during a fire. In this study, the differences in the thermal characteristics of three different extinguishing agents (water, traditional foam, and CAF) were investigated by suppressing a compartment fire. With an ignition source in the compartment (6 m × 3 m × 3 m), the agent was preferentially applied to the outside wall of the compartment. The effects of internal cooling and burnback resistance generated from the outer wall were evaluated. The performance of each agent in shielding firefighters from radiant heat while suppressing the fire inside the compartment was evaluated. When the outside wall of the compartment was covered with each of the agents, all agents were found to reduce the room temperature. When CAF was applied, the delay time until temperature re-rise was approximately 1.76-4.5 times longer than that when water was used. In addition, foaming agents exhibited a higher heat-shielding effect than water during the initial suppression. Thus, considering the thermal characteristics of these agents, fire suppression can be more effective if foam agents are used., Competing Interests: Declaration of conflicting interestsThe authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

• CAF-AFFF extinguishing was studied by the burning rate controlling mechanism. • The increase of flame temperature and radiation after foam discharge was observed. • The foam spreading length with time abides a power law in fire conditions. • The effective and total extinguishing time was defined and analyzed. • Burning rate with extinction time obeys two mechanisms for variable fuel thickness. Compressed air foam (CAF) is an environment friendly fire extinguishing technique being used around the world since the ban of halogen-based agents. In this work, its extinguishing behavior on a radiation-controlled storage tank fire was firstly investigated based on the controlling mechanism of burning rate. A formula of burning rate after foam discharge is deduced. It was found that the oleophobic effect of fluorocarbon surfactants, the increased foam layer thickness and lower diffusion coefficient had coupled chemical and physical effects on extinguishing, which outweighed the cooling effect of foam evaporation. Due to the properties of CAF, a special phenomenon of the sudden increase in the flame temperature and radiation after foam discharge was analyzed. The increase in foam spreading length with time was found to still abide by a power law under fire conditions. A concept of effective and total extinguishing time was suggested, both of which reduce with a rising foam flow rate, but the reduction rate decreases at higher flow rate. In addition, the foam dosage with flow rate had a U-shaped curve at total extinction. For the case of lower fuel thickness, its burning rate was lower and the extinguishing time was longer. [ABSTRACT FROM AUTHOR]

This paper is intended to be the first study to discuss the fire suppressing performance of the four most common extinguishing media under the same reproducible conditions. The tests were performed in bench-scale and used standardized 5A wood cribs as well as a miniature extinguishing system with a liquid flow rate of 1.4 l min − 1. The tests results present a consistent overview of the fire suppression efficacies of water, water with a foaming agent, nozzle-aspirated foam and compressed air foam. Depending on their jet types, the cooling capabilities of the extinguishing media water and water with a foaming agent were compared to the cooling capability of a full jet of wet, general and dry foams. The results show that compressed air foam suppressed fire most effectively under the test conditions. Because of the convoluted crib structure, water and water with foaming agents used from a distance are more effective in the form of a full jet rather than a spraying jet. At close range, spraying jets multiply their effectiveness. A slight difference can be observed in the cooling performance of extinguishing foams that use foaming agents from different manufacturers. The paper establishes a link between the foaming agent's cooling capability and its wetting power by relating the results of wood crib fire tests according to DIN EN 3–7 and findings from laboratory immersion tests compliant with DIN EN 1772. • Systematically applied spraying jets doesn't combat crib fires efficient. • Specifically applied spraying jets combat fires more efficient than full jets. • Systematically applied nozzle-aspirated foams can't develop their full potential. • Compressed Air Foams suppress the fire better than other extinguishing media. • Higher admixing rate doesn't raise the fire-suppression performance to a higher level. [ABSTRACT FROM AUTHOR]

Depopulation of infected poultry flocks is a key strategy to control and contain reportable diseases. Water-based foam, carbon dioxide inhalation, and ventilation shutdown are depopulation methods available to the poultry industry. Unfortunately, these methods have limited usage in caged layer hen operations. Personnel safety and welfare of birds are equally important factors to consider during emergency depopulation procedures. We have previously reported that compressed air foam (CAF) is an alternative method for depopulation of caged layer hens. We hypothesized that infusion of gases, such as carbon dioxide (CO2) and nitrogen (N2), into the CAF would reduce physiological stress and shorten time to cessation of movement. The study had six treatments, namely a negative control, CO2 inhalation, N2 inhalation, CAF with air (CAF Air), CAF with 50% CO2 (CAF CO2), and CAF with 100% N2 (CAF N2). Four spent hens were randomly assigned to one of these treatments on each of the eight replication days. A total of 192 spent hens were used in this study. Serum corticosterone and serotonin levels were measured and compared between treatments. Time to cessation of movement of spent hens was determined using accelerometers. The addition of CO2 in CAF significantly reduced the foam quality while the addition of N2 did not. The corticosterone and serotonin levels of spent hens subjected to foam (CAF, CAF CO2, CAF N2) and gas inhalation (CO2, N2) treatments did not differ significantly. The time to cessation of movement of spent hens in the CAF N2 treatment was significantly shorter than CAF and CAF CO2 treatments but longer than the gas inhalation treatments. These data suggest that the addition of N2 is advantageous in terms of shortening time to death and improved foam quality as compared to the CAF CO2 treatment. [ABSTRACT FROM AUTHOR]

During the 2014-2015 US highly pathogenic avian influenza (HPAI) outbreak, 50.4 million commercial layers and turkeys were affected, resulting in economic losses of $3.3 billion. Rapid depopulation of infected poultry is vital to contain and eradicate reportable diseases like HPAI. The hypothesis of the experiment was that a compressed air foam (CAF) system may be used as an alternative to carbon dioxide (CO2) inhalation for depopulating caged layer hens. The objective of this study was to evaluate corticosterone (CORT) and time to cessation of movement (COM) of hens subjected to CAF, CO2 inhalation, and negative control (NEG) treatments. In Experiment 1, two independent trials were conducted using young and spent hens. Experiment 1 consisted of five treatments: NEG, CO2 added to a chamber, a CO2 pre-charged chamber, CAF in cages, and CAF in a chamber. In Experiment 2, only spent hens were randomly assigned to three treatments: CAF in cages, CO2 added to a chamber, and aspirated foam. Serum CORT levels of young hens were not significantly different among the CAF in cages, CAF in a chamber, NEG control, and CO2 inhalation treatments. However, spent hens subjected to the CAF in a chamber had significantly higher CORT levels than birds in the rest of the treatments. Times to COM of spent hens subjected to CAF in cages and aspirated foam were significantly greater than of birds exposed to the CO2 in a chamber treatment. These data suggest that applying CAF in cages is a viable alternative for layer hen depopulation during a reportable disease outbreak. [ABSTRACT FROM AUTHOR]

During the 2014–2015 US highly pathogenic avian influenza (HPAI) outbreak, 50.4 million commercial layers and turkeys were affected, resulting in economic losses of $3.3 billion. Rapid depopulation of infected poultry is vital to contain and eradicate reportable diseases like HPAI. The hypothesis of the experiment was that a compressed air foam (CAF) system may be used as an alternative to carbon dioxide (CO2) inhalation for depopulating caged layer hens. The objective of this study was to evaluate corticosterone (CORT) and time to cessation of movement (COM) of hens subjected to CAF, CO2 inhalation, and negative control (NEG) treatments. In Experiment 1, two independent trials were conducted using young and spent hens. Experiment 1 consisted of five treatments: NEG, CO2 added to a chamber, a CO2 pre-charged chamber, CAF in cages, and CAF in a chamber. In Experiment 2, only spent hens were randomly assigned to three treatments: CAF in cages, CO2 added to a chamber, and aspirated foam. Serum CORT levels of young hens were not significantly different among the CAF in cages, CAF in a chamber, NEG control, and CO2 inhalation treatments. However, spent hens subjected to the CAF in a chamber had significantly higher CORT levels than birds in the rest of the treatments. Times to COM of spent hens subjected to CAF in cages and aspirated foam were significantly greater than of birds exposed to the CO2 in a chamber treatment. These data suggest that applying CAF in cages is a viable alternative for layer hen depopulation during a reportable disease outbreak.