(Tianjin Fire Research Institute, Ministry of Public Security, Tianjin 300381, China) The effects of time, foam thickness, foam retention time and heat radiation intensity on the thermal insulation performance of compressed air foam. Based on the test, the mechanism of thermal insulation protection of compressed air foam and its main influencing factors were analyzed. At the same time, suggestions were made on how the firefighting unit used the compressed air foam system for thermal insulation protection: fire extinguishing agent; compressed air foam system; Protection: X913, TQ569 logo code: A compressed air bubble system has been widely used in North America and Europe due to its advantages of water saving, high efficiency and heat insulation protection. Compressed air bubbles for the purpose of heat insulation are generally used in forest fires, chemical fires and urban building fires. They can form a protective barrier on buildings or adjacent buildings. Compressed air bubbles are produced compared to traditional low-multiple bubble generation systems. Bubbles, with greater density, smaller particle size, and good bubble uniformity. Researchers have speculated that tiny, fine compressed air bubbles align together and rely on the heat-conducting air contained therein to provide thermal insulation. The role of protection. However, due to the lack of previous testing methods and other factors, the research on the thermal insulation protection mechanism of compressed air bubbles is not deep enough, and the main influencing factors of the thermal insulation performance of compressed air bubbles are not well understood. Therefore, the author studied the thermal insulation performance of compressed air bubbles, and investigated various factors affecting the thermal insulation performance, in order to improve the understanding of the thermal insulation protection performance of compressed air bubbles, scientifically guide the fire fighting and rescue work 1 test equipment and Test method 1.1 Test instrument The test instrument includes a compressed air bubble heat insulation protection performance test device and a test compressed air bubble system heat insulation protection performance test device mainly composed of a radiation plate, a sample plate and an acquisition system, as shown. In order to ensure uniform radiation distribution, two electric radiant panels (600mnK 500mm) V-shaped placement (48 kW per radiant panel) are used. The thermal protection test platform consists of a bracket, a bubble sample plate (600mmX 250mm) and a guide rail for positioning. The bubble sample plate is made of 6mm thick cement plate, and metal retaining rings of different heights can be installed around to make bubbles of different thicknesses to make a small hole in the center of the cement board, and a thermocouple is inserted from the back side to measure the bubble sample plate. Temperature rise situation. The electric radiant panel is placed perpendicular to the ground, and the bubble sample plate is close to the ground (with a very small angle to prevent the bubble from falling off during the test). Distance/cm radiant panel distance-heat radiance intensity curve test The compressed air blister system shall provide compressed air bubbles with state controllable and reproducible for basic research and test. The flow rate is too large, resulting in a bubble far exceeding the amount required for the test; on the other hand, it is not possible to flexibly control the amount and state of the bubble generation, and it is impossible to perform an accurate repeatability test, so that it cannot be used for experimental research and test-specific compressed air. The bubble system solves the above problems well. The installation diagram is as shown in the figure 1.2. The thermal insulation performance test sample and the test variable test select two kinds of compressed air bubble samples at home and abroad, referred to as FoamA and FoamB for short; the selection is representative and Operational Fund Project: Guohao's “Eleventh Five-Year†Science and Technology Support Project “Research on Class A Foam Protection and Fire Extinguishing Performance Evaluation and Application Technology†(2006BAK06B05-4-Set a heat shield (see)) Place the foam sample stage on the guide rail and push it to the position where the test needs heat radiation. Then remove the heat shield and start timing. Collect the foam board The temperature of the thermocouple at the heart position until it reaches the temperature value required for the test. 3 Test results and discussion 3.1 The effect of different thermal radiation intensity on the thermal insulation performance of the foam under the condition of the influence of the thermal radiation intensity of 5 min, as shown in Table 2 Table 2 shows the influence of heat radiation intensity on the thermal insulation protection performance of the valve 10. Foam solution delivery pipe 11. Liquid flow meter 13. Pressure storage tank 17. Installation diagram of compressed air bubble system for intake pipe test According to domestic and foreign materials and In previous studies, the author selected foaming ratio, 25% liquid separation time, foam thickness, foam retention time (that is, the time between the application of foam and the time when the foam was placed in front of the radiant panel to receive thermal radiation) and the thermal radiation intensity. Test variables, respectively, to investigate the effect of the impact on the thermal insulation performance of the foam, measured by the temperature rise lag time of the sample plate, that is, the thermal insulation protection capacity of the compressed air foam mainly reaches 50 ° C and 100 ° C of the sample plate. The lag time indicates that the author also calibrated the temperature rise curve of the blank sample plate (ie, the sample plate without water or foam) at the thermal radiation intensity of 13.978.36 and 5.38 kW/m2. , as shown in the three blank contrast test parameters, as shown in Table 1, heat radiation intensity / kW / m2 expansion ratio 25% liquid extraction time / s up to 50 C time / s up to 100C used by Table 2, the sample The thermal insulation protection of FoamA decreases with the increase of thermal radiation intensity. It can be seen from the comparison of the test parameters in Table 1 that the application of foam has a certain effect on the temperature rise hysteresis. The thermal protection ability of the sample FoamB also increases with the increase of the thermal radiation intensity. The authors speculate that the compressed air foam has thermal insulation protection mainly because the large amount of air contained in the foam is a poor conductor of heat, and it has a certain heat insulation effect on the sample plate at the initial stage of temperature rise. High, the foam gradually ruptures until it disappears, and the cooling effect changes from foam to water, and water also has a certain effect on the temperature rise lag of the sample plate.
2 The effect of foam thickness on the insulation performance of foam under the condition of 97kW/m2, such as the influence of the thickness of the bubble on the thermal insulation performance of the foam. The thickness of the foam/cm reached 50C/s the time taken to reach 100C/ S383226112357 After the electric radiant panel is started for 20 minutes, the heat radiation is balanced to a suitable mixing ratio, and the compressed air foam system is tested to produce a suitable foaming multiple of the heat-insulating protective foam at a flow rate of 11. and sprayed to the desired thickness. On the foam sample plate of the retainer, use a ruler to scrape off the excess foam. Between the electric radiant panel and the foam sample plate, it can be seen from Table 3 that the greater the thickness of the foam cover, the better the heat insulation protection effect. This is more evident in the relatively low heat radiation intensity conditions. For the test sample FoamB, the thermal insulation performance also increased with the increase of the foam thickness. However, in the actual fire field application process, the thickness of the foam is subject to the actual fire conditions, and cannot be increased indefinitely. Therefore, it is recommended that the fire department comprehensively consider the foam adhesion ability of the protected object, the flame spread speed, the supply capacity of the fire water, and the compressed air foam. The actual fire conditions such as performance and reserve are used to determine the appropriate foam coverage thickness.
3 The effect of foam residence time From the actual use of compressed air foam, it is required to compress the blank plate heat radiation intensity / kW / m2 to reach 50C / s to reach 100C air foam has a certain foam retention time, that is, compressed air foam After being retained for a period of time on the protected building, it is still necessary to maintain a certain degree of thermal insulation protection. In this way, the impact of the 5,515 min3 residence time on the thermal insulation performance of the compressed air foam is examined in the actual application value test. The foam has a thickness of 6 cm and a heat radiation intensity of 8.36 kW/m! The test results are shown in Table 4.
Table 4 Effect of bubble retention time on foam insulation performance The most important indicator of gas foam insulation performance, because 25% precipitation time is an important indicator to measure foam stability, the longer the 25% liquid separation time, the more foam Stable, heat-resistant radiation ability is also more than 25% of the compressed air foam with a liquid separation time of more than 20min, will effectively play the role of heat insulation.
5 foaming multiple effect bubble retention time / min sample name 25% liquid extraction time / s expansion ratio up to 50 ° [: time / s up to 100 time / s5Foam 36kW / m2, foaming multiple for temperature rise The influence of lag time, see Table 5, Table 5, the expansion factor of the foam insulation protection performance, the impact of five factors on the thermal insulation performance of compressed air foam, as shown in Table 6 Thermal radiation intensity Bubble thickness Foaming multiple 25% Eluent time Bubble retention time and compression air bubble insulation protection performance inverse proportional to proportional proportional to inverse ratio As can be seen from Table 4, with the increase of residence time, foam insulation protection The ability to gradually reduce the concentration of FoamB, especially 25% of the liquid extraction time less than 10min, after 15min retention, the thermal insulation protection capacity decreased significantly; after 30min retention, the thermal protection ability decreased more. The sample FoamA, which has a 25% solution time longer than 30 min, has a relatively small thermal insulation protection effect due to the residence time.
3.425% of the time of liquid separation can be seen from Table 4, the thermal insulation protection capacity of the foam is proportional to the 25% of the foaming time of the foam, and the heat-insulating protective foam has a long time of 25%. It should be specially pointed out that the foam sample plate in the test uses a cement plate with a thickness of 6 mm, and the cement plate has strong water absorption. However, in reality, the actual fire conditions are complicated, the building materials are various, and the water absorption is mostly worse than the cement plate. . In order to ensure that the test can be effectively compared, and the sample plate with strong water absorption capacity and easy adhesion and coverage is selected, the 25% liquid separation time also affects the adhesion ability of the heat insulation foam to the protected object, 25% liquid extraction. The long-term heat-insulating protective foam has good adhesion to most building materials, ensuring that its thermal insulation effect can be effectively utilized, that is, it can provide thermal insulation protection for a longer period of time and 25%. The heat-insulating protective foam with short liquid-discharging time has poor adhesion on the surface of most building materials and cannot effectively cover the vertical surface of the building. It can not effectively exert its heat-insulation protection. Due to the test conditions and time, the author No quantitative correlation between 25% liquid separation time and foam adhesion ability is obtained. Furthermore, 25% of the compressed air foam with a long liquid separation time has a relatively high foam viscosity, which can provide a larger foam cover thickness, thereby improving compression. The thermal insulation protection performance of air foam is summarized above. The author believes that 25% of the liquid separation time is a measure of the compression space. As can be seen from Table 5, the higher the foaming ratio, the foam reaches 50 °C and The longer the time of 100 °C, the higher the foaming ratio, the better the heat insulation protection performance of the foam. When the foaming multiple is more than 30 times, the heat insulation protection effect can be obtained. In addition, the test proves that the foaming is higher. Multiples of foam typically have a longer 25% time to liquid. Therefore, the expansion ratio of the compressed air foam used for heat insulation protection should be greater than or equal to 30 times, and the higher the expansion ratio, the more "light" the foam, and the easier it is to adhere to the surface of the protected building, at the same quality. In this case, the thickness of the foam cover and the heat insulation protection ability of the foam can be improved, but the more "light" the foam, the more susceptible it is to the external conditions such as wind, and it is easy to be blown away. Therefore, under actual fire conditions, 30 times or more. It is a suitable foaming multiple and the firefighting unit should pay attention to the foaming ability of the foam fire extinguishing agent when it is equipped with the foam fire extinguishing agent for the compressed air foam system. 3.6 Test conclusion At present, the compressed air foam system at home and abroad uses foam fire extinguishing. The main difference in the performance of the agent is basically the difference of 25% of the time of liquid separation. The length of the 25% liquid deposition time depends mainly on the composition of the fire extinguishing agent itself, and determines the heat insulation protection ability of the fire extinguishing foam. Therefore, it is recommended that the firefighting force require the foam supplier to provide the technical parameters of the foam in the compressed air foam system when configuring the foaming agent for the compressed air foam system, including the 25% precipitation time, expansion ratio and other indicators. The indicators meet the requirements, in order to ensure the advantages of the compressed air foam system, to meet the actual requirements of fire fighting and rescue actual combat fire extinguishing agent and flame retardant materials organic halogen flame retardant fire smoke toxicity evaluation He Wei, Dong Xilin, Wu Lizhi (China The People's Armed Police Force Academy, Langfang 065000, Hebei Province, studied six categories of toxicity indicators such as human toxicity, ecotoxicity, and photochemical smog, and gave calculation methods for the latent values ​​of each affected category. On the basis of various individual impact indicators, the toxic effect indexation equation was proposed, which can easily and comprehensively evaluate the comprehensive toxicity effects of organic halogen flame retardant combustion products.
In order to reduce the fire hazard caused by the heavy use of flammable materials, flame retardant treatment of flammable and combustible materials is required, which makes the flame retardant materials rapidly develop organic halogen flame retardants (including bromine and chlorine flame retardants). ) is the largest organic flame retardant organic halogen flame retardant material has a certain negative impact on human health and ecological environment during use. When a fire occurs, the decomposition and combustion of halogen-containing materials will generate a large amount of smoke, which is contained in smoke. A variety of toxic gases, and the smoke is hardly reduced during a fire. In order to correctly estimate the dangerous situation of fire smoke toxicity, the author comprehensively studied the indexation method of the toxicity of organic halogen flame retardant fire smoke, and explained the calculation of the potential value of organic halogen flame retardant (potential toxicity influence ability). method.
1Combustion products and toxicity The causes, conditions and environment of each fire are different. The combustion products vary widely and the composition is very complicated. Generally, the smoke generated by fire is mainly composed of the following four types of substances with higher temperature. Uniform mixture: 4 Conclusion According to the test results of thermal insulation performance research, it is recommended that the fire department pay attention to the following points when using compressed air foam fire truck for the purpose of heat insulation protection: try to increase the thickness of foam cover, the greater the thickness of foam cover, The better the thermal protection effect.
Try to choose a relatively high expansion ratio, generally should be 30 times more than 25% of the time of the liquid separation time, the more obvious the heat insulation protection effect 25% liquid extraction time should be greater than 20min to have better insulation protection effect The author recommends that the fire department should select 25% compressed air foam fire extinguishing agent with a liquid separation time of at least 20min (20°C) when configuring compressed air foam to better exert the heat insulation protection of compressed air foam fire trucks. ability.
Compressed air foam fire extinguishing agent premix ratio is usually chosen.
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