Effect of temperature in the occurrence of backdraft Tseng, Tzu-Yan; Wu, Chia-Lung; Tsai, Kuang-Chung
Journal of loss prevention in the process industries,
February 2024, 2024-02-00, Volume:
87
Journal Article
Peer reviewed
Many previous studies have investigated the mechanism of backdraft, focusing on the flammable gas concentration. However, there still exists a question: whether temperature is influential. This study ...visited this topic with compartment fires in the “fully developed fire period” and under-ventilated, i.e. after flashover and before “decay period”. It was the first research investigating backdraft with compartment fires in which the door was open during this fully-developed fire period. The compartment fires were fuel-rich, and fit the theoretical definition of backdraft. The compartment size was 0.8 m (L) × 0.4 m (W) × 0.4 m (H), and the size of the opening was 0.4 m (W) × 0.13 m (H). The fuel was wood cribs. The time to flashover was 350 s after ignition, and the door was closed at 450 and 510 s. The doorway closing duration was 60, 120 and 240 s. Experimental results reveal that the compartment temperature declined as the doorway closure duration increased. The likelihood of backdraft consequently decreased, and the time to backdraft occurrence after opening the door (delay time) increased. Backdraft became more difficult to achieve as the compartment temperature decreased. This observation may be caused by weak gravity current generated due to low compartment temperature. Consequently the compartment temperature is influential in the occurrence of backdraft.
•The compartment temperature is influential to the occurrence of backdraft.•The likelihood of backdraft decreases when the compartment temperature declines.•Backdraft occurs late when the compartment temperature declines.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
La production de fumées, l’embrasement généralisé (flash-over) et l’explosion de fumées (backdraft) sont les 3 principaux phénomènes thermiques observés dans les incendies. Les fumées, produites par ...tout incendie sont responsables de 90% des décès observés dans ces circonstances. Flash-over et backdraft se produisent lors des incendies en milieu confiné. Très difficilement prévisibles, ils sont responsables de nombreux accidents touchant les sapeurs- pompiers en intervention. Quelques règles simples de construction et de prévention dans les habitations permettraient de limiter le nombre et la gravité de ces incendies.
Backdraft is a special phenomenon in fire research because of its explosive consequence and the occurrence of uncertainty. The delay time of occurrence has been of interest in recent years as this ...influences the safety and efficiency of firefighting. This paper investigated the location of the opening and whether it affects the delay time of the backdraft. Results show that the location of the opening dramatically dominates the delay time. The hot/cold air mixing path and instantaneous localized fire ignitions determine the delay time. A ‘curtain-like’ effect for the backdraft time delay was observed. The lower opening demonstrates about 50–70 % delay time compared to the upper and middle locations. In the presence of identical fire conditions and door closure control, the extended flammable gas dilution resulting from the upper opening does not significantly impact the onset of backdraft. Hence, the effective volume above the ignition location determines the delay time of the backdraft. Furthermore, the choice of chamber material is a crucial factor influencing the likelihood of backdraft occurrence. Utilizing a material with enhanced cooling capacity reduces the probability of backdraft. This provides insight into the firefighting and intervention tactics when ventilation-restricted compartment fire occurs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This work examines the influence of gas mixture compositions on backdraft phenomenon. A series of experiments were conducted in a reduced-scale enclosure subjected to various fire configurations, ...including a 25.0 kW and a 37.5 kW methane fire and a 16.7 kW and a 25.0 kW propane fire. Three different metrics were used to evaluate backdraft phenomenon: (1) internal conditions within the enclosure before an anticipated backdraft; (2) ignition of a local gas mixture resulting in a backdraft; and (3) intensity of resulting backdraft. The gas mixture composition within the compartment before a backdraft was determined using measurements obtained from an enhanced phi meter and gas analyzer. Ignition resulting in a backdraft was evaluated from the equivalence ratio and gas species concentration measurements surrounding a triggered spark ignitor. Backdraft intensity was analyzed by quantifying the total heat release of the exiting fireball via carbon dioxide generation calorimetry. Real-time equivalence ratio measurements showed the progressive state of the gas mixture composition within the compartment before ignition. Backdraft was observed to occur when the gas mixture surrounding the ignition soure was greater than stoichiometric conditions. The total heat release of backdrafts was found to correspond to the initial mass fraction of fuel residing within the compartment for experiments with propane fires.
•A series of backdraft experiments were conducted in a reduced-scale enclosure.•Gas mixture distribution and internal density varied via compartment configurations•The gas mixture density impacted the mixing dynamics of the incoming gravity current.•Ignition was achieved for rich gas mixtures surrounding a charged spark ignitor.•A backdraft’s total heat release increased with the initial mass fraction of propane.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study investigates the burning history of medium-density fibre (MDF) cribs in an underventilated enclosure with two vertical openings in the front wall. Such compartment fires have been explored ...before by other researchers and demonstrated the conditions that would lead to smoke explosions (Sutherland, 1999; Chen, 2012) 1,2. A total of 19 experiments were completed, 5 of which led to smoke explosions. A gas conditioning system is utilised for the experiments which included a hydrocarbon analyser and an enhanced Phi-meter. Heat release rate, mass loss rate, temperatures, pressures, and O2, CO2 and CO gas concentrations within the compartment are measured for each experiment. Compartment fires with MDF crib fuel in underventilated conditions can lead to smoke explosions for both porosity-controlled and surface-controlled cribs. The smoke explosion is found to be occurring when the changes of pyrolysate gases and oxygen concentrations in the compartment form a flammable mixture. The equivalence ratio of the compartment was found between 1.5 and 2.0 before the occurrence of smoke explosions. Transformation of flaming combustion to smouldering was generally observed as a precursor for the accumulation of unburned fuel and the occurrence of smoke explosion.
•Difference between smoke explosion and backdraft is reviewed.•The occurrence of smoke explosions is explained by experimental work.•Transition to smouldering was generally observed as a precursor of smoke explosion.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
An extensive set of backdraft experiments has been performed at the NIST National Fire Research Laboratory. These experiments were conducted in a reduced scale compartment, and are part of defining ...the conditions conducive to backdraft. Further, the detailed chemistry and heat measurements are intended to evaluate computational fire models. In this article, we describe the modeling effort employing the Fire Dynamics Simulator (FDS) in simulations involving different fuels and ignition source locations mirroring a subset of the named experiments. We focus on using default simulation parameters and study their effect on the backdraft outcomes. In particular, the ignition model’s temperature threshold and ignition procedure play a primary role in developing a backdraft.
•Initial conditions for fire models are based on a dataset of backdraft experiments.•Chemical composition and heat measurements are intended to assess fire models.•FDS with fast chemistry is exercised on some of these backdraft scenarios.•Ignition model temperature threshold and procedure are critical for backdraft outcome.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Backdrafts are violent events that occur when oxygen is suddenly introduced to an oxygen-depleted compartment fire and are primarily driven by the presence of gravity currents. However, with human ...travel potentially expected beyond the confines of earth gravity, it is not clear how the magnitude of the gravity constant can contribute to the intensity of these events. This issue can be relevant when dealing with fires on space stations or on future bases on the Moon and Mars. In this study, we carry out backdraft simulations in a compartment under different reduced gravity conditions using the NIST Fire Dynamics Simulator (FDS) code. A combustion compartment, initially containing under-ventilated heated methane, is opened to the surroundings using a vertical opening slot. Through the bottom of the opening flows a gravity current of oxygen. When the current reaches the far wall of the combustion compartment, the mixture is ignited, and a violent backdraft event occurs. Measures of heat release, fire development, and pressure rise suggest that the effects of backdraft are highly nonlinear based on the gravity constant. Even small values of the gravity constant (as low as 0.01g) can trigger relatively strong backdrafts.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PM2.5 emissions from cooking are harmful to human health, and kitchen ventilation is an effective method to reduce the PM2.5 concentration. Cooking exhaust shaft system is a ventilation system widely ...used in kitchens of residential buildings. However, there is a reverse flow of cooking emissions and odor migration in cooking exhaust shaft system because of the air leakage of backdraft dampers. The aim of this paper is to quantify the airtightness of backdraft dampers and their effect on air quality. There are two types of backdraft dampers widely used in residential cooking exhaust shaft system in China. The blade of one type of damper has two bearing points on the frame and the other type of damper has one bearing point. A total of 40 backdraft dampers (20 Two Bearing Points and 20 One Bearing Point dampers) were selected to test airtightness. Test results show that the airtightness of the 40 backdraft dampers varies greatly, with the air leakage ranging from 7 m3/(h·m2) to 846 m3/(h·m2) at a static pressure difference of 250 Pa. Of the 40 dampers, only 18 One Bearing Point dampers have air leakage lower than 366 m3/(h·m2) specified in ASHRAE Standard 90.1–2016. It is recommended that the One Bearing Point dampers should be utilized in the residential cooking exhaust shaft system. Using the poor, medium, and good One Bearing Point dampers in residential cooking exhaust shaft system for different floors, the air leakage of the closed backdraft dampers is simulated, and the result is 0.6 m3/h ~8.0 m3/h with different rates of simultaneous use. These air leakages may cause the PM2.5 concentration in non-cooking kitchens to exceed the WHO Interim Target-1 of 35 μg/m3. It is suggested a stricter airtightness standard of backdraft damper should be formulated, and the air leakage of backdraft damper should not be greater than 1/5 of the ASHRAE standard specified value.
•Airtightness of 40 backdraft dampers widely used in China was tested.•There is air leakage of the closed backdraft dampers in the cooking exhaust shaft system.•Stricter airtightness standard for backdraft dampers should be formulated than ASHRAE Standard 90.1–2016.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
For more than a century, smoke explosions have been documented in the fire research literature. Yet even with this long history, smoke explosions have received very little attention in the fire ...research community. The few review articles on unexplained explosions (overpressure events) have adopted the conventional names of smoke explosions, backdraft, smoke gas explosions or rapid fire progression. Anecdotal evidence from firefighters have shown a number of overpressure events that cannot be explained as a gas leak or flammable liquids ignition. In this study, experiments were conducted in a plywood lined compartment with a timber crib as a sustained fire source and the ignition source. The compartment had a single vent that was open for the entire time. After an extended period of burning, the flames detached from the crib, traveled around the compartment, and finally self-extinguished. Sometime after the flames self-extinguished, the compartment erupted in flames culminating in a large horizontal flame projecting more than 2 m from the vent opening. In this study, a consistent cycle that leads to an overpressure event has been identified. A total of 29 overpressure events were created in 13 experiments with many experiments experiencing multiple overpressure events. Gas species, compartment temperatures, vent velocities, and compartment pressure were all recorded during the experiments. Conditions in the compartment immediately prior to the overpressure event are reported. Having demonstrated that an overpressure event within a combustible compartment can be reproduced, future research is recommended to better quantify the conditions leading to an overpressure event.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
