Key Engineering Materials Vol. 954

Abstract: Halons are usually used for fire extinguishing where other types of extinguishing agents cannot be used. Their use does not require disconnection of electrical networks, does not lead to any damage, and after airing the premises, these substances do not leave any residues. Halons are used as flame retardants in concentrations (from 2 to 12% vol.). In the case of their use, a decrease in the oxygen content in the air of the flame center’s due to dilution is not significant, and extinguishing occurs as a result of the slowing down and interruption of chain chemical reactions in the flame. Combustion inhibitors play the role of a "negative catalyst", the mechanism of their action consists in high reactivity to interact with radicals with the formation of inert compounds, thereby interrupting the chain reaction of combustion and slowing down its development. The concentrations of bromotrifluoromethane (halon 1301) and 1,2-dibromotetrafluoroethane (halon 2402) in the mixtures were determined by the gas chromatographic method, and experimental researches for determining the minimum fire-extinguishing concentration established that the halons 1301 and 2402 mixtures show high efficiency in extinguishing flames. Established, that the mixture of halons 1301 and 2402 with the concentration of the latter in the range of 60÷65% exhibits the best minimum fire-extinguishing concentration. At these values, the minimum fire-extinguishing concentration did not exceed 2.0% vol. It was determined that when reducing the concentration of oxygen in the air by halon 1301 from 20.5 to 19% of volume, the concentration of halon 2402 for extinguishing n-heptane decreases by 2.5 times. Inhibition of the n-heptane flame combustion process by such mixtures of halons is associated with the decomposition of halons under the influence of temperature with the absorption of heat and releasing of combustion inhibitors, a change in the direction of decomposition towards the formation of non-combustible gases and the cessation of oxygen access. This indicates possibility of using available gas extinguishing substances - halons - for fire extinguishing.

Abstract: The contributions balance of isolation and cooling effects relative to the liquids surface to slow down their evaporation and to achieve safe vapor concentrations is determined. The influence of liquids characteristic temperatures and their water solubility on this process is considered. It is proven that the long-term effect of such means is provided by systems based on closed-pore floating solid materials (for example, foam glass). It is proposed to increase the foam glass low isolation and cooling capacity either by coating it with an inorganic gel or by wetting it with water. Smaller evaporation retardation coefficients by gel were obtained for liquids with the higher water solubility. A 5–6 times greater cooling capacity of the wet foam glass than dry foam glass was obtained for both polar and non-polar liquids. A smaller cooling effect is observed for liquids with a higher vaporization heat and is similar for both the use of the dry and wet foam glass. It was found that for low-boiling non-polar liquids, the evaporation slowing down is more effectively achieved by using isolation effects, and for high-boiling polar and non-polar liquids - by using cooling effects. It is proved that the fire extinguishing effect by applying the foam glass layer on the flammable liquid surface occurs in a similar way for liquids with close equivalent cluster lengths and not flash temperatures.

Abstract: The paper discusses the influence of flame retardant compositions obtained in the system of silicic acid sol (SiO₂ sol) – flame retardants on the fire retardant properties of thin dense cotton fabrics and low density voluminous tapestry fabrics. The need to develop the optimal composition of a fire-retardant composition for a specific fabric, or to unify it for two main groups of fabric: thin and bulky low-density ones, is substantiated. Experimental coatings were obtained by applying SiO₂ sol, which was obtained by the reaction between liquid glass and acetic acid, followed by application of flame retardant solutions (diammonium hydrogen phosphate (DAHP) and urea) by spraying or by the bath method. As a result of the optimization, using the central composite uniform rotatable plan of the second order, it was established that the main effect of the flame retardant is exerted by diammonium hydrogen phosphate (DAHP). The content or concentration of urea depends on the concentration of DAHP used: if diluted DAHP solutions (9–10 %) are used, trace amounts of urea (0–0.5 %) must be added. In the case of using a concentrated DAHP solution (18–20 %), the concentration of the urea solution should also be increased to 8–10 %.

Abstract: By introducing, in addition to phosphorus, nitrogen and halogens into the structure of the organosilicon compound, a synergistic effect of the flame retardant effect of the fabric is achieved, but the issue of protecting the environment from the effects of thermal decomposition products of the flame retardant composition arises. In view of the numerous publications on the impact of thermal destruction products of flame retardants on the ecological state of the environment, the problem of finding safe types of flame retardants that do not release toxic decomposition products during thermal destruction has arisen. The aim of the work was to develop a phosphorus-and nitrogen-containing silicate fire-retardant composition based on safe components that do not produce toxic products during thermal destruction of the treated fabric. As a result of the conducted research, it was established the possibility of using modifying additives (orthophosphoric acid and ammonium dihydrogen phosphate) in the composition of protective sol based on liquid glass. It was established that the introduction of small additions of orthophosphoric acid into the SiO₂ золь сприяє утворенню суцільних тонких кремнеземних плівок на поверхні волокон ниток бавовняної тканини та значно збільшує час початку руйнування тканини під дією вогню. Позитивний результат досягався за умов одноразового просочування золем низької концентрації (8% SiO ₂ ). Встановлено, що додавання дигідрофосфату амонію також позитивно впливає на підвищення вогнезахисних властивостей тканини. Оптимальний діапазон концентрації розчину фосфоровмісної добавки становить 10-15%. Додаткове просочення вогнезахисним розчином підвищує вогнестійкі властивості текстильних матеріалів і перешкоджає остаточному прогоранню і тлінню.

Abstract: To extinguish flammable liquids, it is suggested to use a multi-component fire extinguishing system consisting of two layers. The first layer is designed to ensure the buoyancy of the fire extinguishing system. It is suggested to use crushed foam glass as the material of this layer. As the material of the upper layer, it is suggested to use light dispersed materials with increased thermal insulation properties. As such materials, the use of exfoliated perlite and vermiculite is justified. To increase the insulating and cooling properties of the fire extinguishing system, wetting of the upper layer with water is used. Bulk density, buoyancy in heptane and moisture retention of crushed foam glass, expanded perlite and vermiculite were experimentally determined. The insulating properties of binary layers of foam glass + perlite and foam glass + vermiculite were studied. The heights of the layers of dry and wet bulk materials necessary for extinguishing heptane were determined experimentally. A conclusion was made about the advantages of the proposed fire extinguishing system based on light bulk materials compared to the existing fire extinguishing means.

Abstract: У даній роботі представлено спосіб створення гелевої вогнегасної речовини на основі гідроксиду алюмінію з використанням карбонату калію. Показано переваги запропонованого способу порівняно з відомим способом створення гелевої вогнегасної речовини на основі гідроксиду алюмінію з використанням карбонату натрію. Наведено результати експериментальних досліджень ефективності гелевогнегасних речовин на основі гідроксиду алюмінію.

Abstract: The factors influencing the screening of thermal radiation by environmentally friendly aerosols have been theoretically substantiated and experimentally determined. The processes of absorption and scattering of thermal radiation have been analyzed.

Abstract: The paper analyzes the risk of spontaneous combustion of grain products during storage. It has been established that there is an annual increase in the number of fires at grain elevators. The article presents a method for early detection of a fire hazardous state of a grain embankment, in which, by means of preliminary laboratory modeling, the construction of experimental dependences of the temperature of a grain embankment on time is provided. It is shown that due to this, the accuracy of predicting the critical characteristics of a grain embankment increases. It has been experimentally proved that preliminary laboratory identification of the parameters of the law of temperature change and the construction of a diagram of the dependence of the temperature of a grain embankment on time allows in production conditions to determine in advance the time to reach a risky temperature value.

Abstract: As a result of the studies of wood flame retardant effect on ignition, the parameters of flame propagation and combustion suppression were established, which makes it possible to influence this process. It has been proven that the creation of a protective layer on the surface of wood prevents it from heating up to a critical temperature. At this moment, a certain amount of combustible gases is released, that is, intense decomposition and ignition occurs. This knowledge makes it possible to establish the dependence of the process of inhibiting the burning rate of wood on the quality of fire protection and the properties of the applied protective mixtures. By experimentally examining wood samples, it was established that the sample without treating caught fire on 52 s and in 100 seconds the flame spread over the entire surface, the sample fire-retardant "FIREWALL-ATTIK" did not catch fire, impregnating solution ВС-13 and "FIREWALL-SV-1", namely a mixture of 271.1 g/m², took 570 and 560 s, the flame spread to the surface only in areas closer to the source, the highest flue gas temperature of 86 and was reached more than 5 times faster, and the flammability index decreased to 4. For the sample protected by "FIREWALL-LAC" ignition occurred in the last second, the flame was recorded at level 0. For the sample fire-protected by "FIREWALL-WOOD" coating no ignition occurred, combustibility index is 0. Due to this, it became possible to determine the conditions for changing the combustion barrier to heat conductivity. Correspondence between the obtained experimental results of the wood burning rate and the analytically calculated equations was found.Taking into account the above, there is a basis for asserting the possibility of purposeful management of the processes of protecting wood from fire by applying fire-retardant mixtures, which under certain conditions are able to create a protective layer on the surface of the material, which restrains the growth of the rate of wood burning.