Backdraft Research Articles

Experimental investigation of the smoke explosion phenomenon

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.

Flammability of engineered wood pyrolysis gases at anaerobic condition

This study aims to quantify the flammability limits of the pyrolysate gases produced from thermally decomposed medium density fibreboard (MDF) and plywood. Finding the flammability limits of the pyrolysate gases is believed to assist in studying the smoke explosion phenomena as smoke explosion is known to be caused by gradual transformation of the oxygen and smoke gas mixture to a flammable mix.A novel gas generation apparatus is developed to generate pyrolysate products from thermally decomposed engineered wood materials, filter the aerosols and condensates, and store the pyrolysate gas in a sealed chamber. The flammability of the pyrolysate gas is then tested in a flammability testing apparatus similar to the apparatus developed by the U.S. Bureau of Mines. The operation of the flammability test apparatus is verified by measuring the flammability limits of methane. The flammability limits of MDF and plywood pyrolysate gases found by experiments are in good agreement with the flammability limits found based on the species distribution of engineered wood pyrolysis, reported by other researchers. Quantifying the flammability characteristics of engineered wood pyrolysate gases is part of ongoing research to understand the effect of smoke species on fire behaviour and on the occurrence of smoke explosion.

Experimental investigation of underventilated fires in enclosures with two front vertical openings and occurrence of smoke explosions

In addition to classical compartment fire development stages, smoke explosions can occur for underventilated conditions while the ventilation openings remain the same. Smoke explosions are different from backdrafts, involving changes in ventilation by additional openings. In this study, the burning history of medium-density fibre (MDF) cribs located at three different elevations has been investigated for the first time in an underventilated enclosure having two vertical openings at the front wall. The effects are examined of different fuel locations, the crib geometry and the ventilation on the mass loss and heat release rates. The fuel mass loss and heat release rates being nearly independent of the crib location and type depend on a new ventilation parameter determined from the distance between the two openings in a simplified way including effects of mass pyrolysis rate and gas temperatures. The mass air inflow is also proportional to this ventilation parameter and independent of the gas temperatures. In some experiments, however, the fires produced single or multiple smoke explosions after a dip in the heat release rate ejecting flames outside. The occurrence of a smoke explosion in relation to the porosity of crib, appearance of smouldering and the vitiated environment is also discussed.

Numerical investigation of backflow in natural draft chimneys

Natural draft chimneys are the traditional chimneys, which are being the most used because of its low cost and simple design compared to solar and other smart chimneys. However, the use of traditional chimneys reported the problem of back drafting particularly in colder regions. Utilization of various suction devices such as exhaust fan, vacuum cleaner and dryers lead to the development of negative pressure inside the house, which in turn causes possibilities of back drafting in chimneys. This allows the outside air to get into the house and affects the entire ventilation system. Stack effect of dwellings and other environmental factors such as seasonal temperature and pressure changes are the influential factors for back drafting along with the furnace on and off conditions. A numerical analysis of the flow of motion in the chimney was performed to visualize its behavior under all conditions including back drafting. CFD simulation results shown that the inside pressure gradient and temperature gradient of chimney determine the direction of hot dry air gases because of the variation in density of gas with respect to temperature change. The numerical study can be used to modify the design of vertical chimney duct such that flow can get only accelerated on moving towards the top of the chimney.

Green Marketing Practices of Manufacturers in Virudhunagar District

Eco-care has rapidly come out as a worldwide happening. Marketers have risen to the circumstance and have started reacting to ecological confronts by practicing eco-care marketing approach. The alertness of the Eco- friendly buying and selling activities are maximized among the Indian consumers. Many of the producers are keeping touch with Green marketing practices in India. So, the Green marketing thought is not the new survival mantra of the business units. Eco-friendly has added thrust in the perspective of global warming and weather change; they have forced producers to integrate the principle of eco-friendly buying and selling processes. As resources are minimized and individual wants are maximized, resources have to be used reasonably and in an eco-friendly mode. Therefore, it is necessary for the manufacturers to reconsider their business strategy to make the manufacturing process as eco-friendly way. With this back draft, the researcher makes an attempt to analyze the practices of manufacturers regard with green marketing in Virudhunagar District of Tamil nadu. For that purpose, the factor analysis has been applied and the inference was made.

Optimisation of Multi-Response Surface Parameters of the Roving Twist Factor and Spinning Back Zone Draft

In order to obtain the optimal collocation of two important technological parameters in the spinning process, the multi-response surface method was used to optimise the experimental results. Through the orthogonal design of the two factors and four levels of factor encoding, 16 groups of orthogonal experiments were designed; the experimental results were fit using the curve fitting toolbox of Matlab; a regression equation of yarn quality indicators, and in addition to a three-dimensional surface chart, an optimal scheme of the roving twist factor and spinning drafting for a roving twist factor of 110 were established; a spinning back draft of 1.5 was obtained based on experimental results of the response surface analysis and variance regression analysis. Experiments on the optimal scheme were carried out to verify the practicability of the results obtained by this method. The results show that application of the multiple response surface method to the optimisation of process parameters is of practical significance. This method can be applied for the optimisation of other process parameters.

Inwards Doors Blocked by Fire Induced Overpressure in Airtight Apartment: a Real Case in Germany

Nowadays, construction requirements and practices are rapidly moving towards more airtight building envelopes, thermal insulation and energy saving according to the Energy Performance of Buildings Directive. In such structures, one might wonder if there are specific risks in case of fire. Some fatal accidents during the intervention of fire brigades were reported in the past due to a backdraft phenomenon in airtight and insulated renovated apartment. However, the occupants of better insulated and sealed buildings can also be exposed to news kinds of hazards. This paper presents the fire that occurred in an apartment in Germany on the 5 February 2013. This fire broke out during night in an apartment in a newly renovated building to meet the passive standard. Awakened by the noise of the flames, the occupant of the apartment quickly noticed that a fire had just broken out in his living room. After an unsuccessful attempt at fire extinction, he decided to abandon his dwelling. Unfortunately, the inwards-opening door to reach the outside via the corridor turned out to be completely blocked. After an interminable waiting period estimated by the investigators of nearly two minutes the occupant was finally able to open the bedroom door leading to the balcony where he was rescued by the emergency services and escaped with burns. After some investigations and based on fire simulations results from CFAST modeling, it was concluded that the door were blocked due to the fire induced overpressure.From this real fire case there is no doubt about the capacity of the building structure to withstand high levels of overpressure, the integrity of the sealing of the passive house being not deteriorated in the first moments of the fire. This new fire hazard has to be taken into account in the fire safety design of confined dwellings.

The Co-creation and Feasibility of a Compassion Training as a Follow-up to Mindfulness-Based Cognitive Therapy in Patients with Recurrent Depression

The aim of this study was to assess the feasibility, acceptability and preliminary effectiveness of Mindfulness-Based Compassionate Living (MBCL) as a follow-up intervention to Mindfulness Based Cognitive Therapy in adults with recurrent depression. We conducted an uncontrolled study in 17 patients with recurrent depression, in two successive groups. The first group contained novices to compassion training (N = 14); in the second group, ten of these participated again, in addition to three new participants (N = 13). The overall group contained 15 females and 2 males, aged between 37 and 71. The MBCL program was qualitatively evaluated using post-intervention focus group interviews in both groups. In addition, self-report questionnaires assessing depressive symptoms, worry and both self-compassion and mindfulness skills were administered before and after MBCL. No patients dropped out of the intervention. Average attendance was 7.52 (SD 0.73) out of eight sessions. Helpful elements were theory on the emotion regulation systems, practicing self-compassion explicitly and embodiment of a compassionate attitude by the teachers. Unhelpful elements were the lack of a clear structure, lack of time to practice compassion for self and the occurrence of the so-called back draft effect. We adapted the program in accordance with the feedback of the participants. Preliminary results showed a reduction in depressive symptoms in the second group, but not in the first group, and an increase in self-compassion in both groups. Worry and overall mindfulness did not change. MBCL appears to be feasible and acceptable for patients suffering from recurrent depressive symptoms who previously participated in MBCT. Selection bias may have been a factor as only experienced and motivated participants were used; this, however, suited our intention to co-create MBCL in close collaboration with knowledgeable users. Examination of the effectiveness of MBCL in a sufficiently powered randomised controlled trial is needed.

Defining the Difference between Backdraft and Smoke Explosions

Compartment fires are commonly discussed in the classical sense with the compartment fire growth history starting with the incipient phase leading into the growth phase that transition through flashover into the fully developed phase and ends in the decay phase. However, when a fire starts in a closed compartment where only ventilation is the leakage available, the fire can start to smolder and produce large quantities of CO and unburned hydrocarbons. These products of incomplete combustion accumulate in the compartment and create an extremely hazardous condition. If the conditions are right and a large vent becomes available, such as a fire fighter opening a door, a rapidly developing flame front spreads through the enclosure burning the available fuel that has mixed with the incoming air, culminating in a large fireball outside the opening. This catastrophic event is known to fire fighters as a backdraft and by definition requires a sudden change it the ventilation. Anecdotal evidence supports a different phenomenon in which a closed compartment suddenly erupts in flames breaking glass and even causing structural damage without a vent ever being open. This phenomenon is referred to here as a smoke explosion. Recent work has focused on improving our understanding of these poorly understood events and the conditions that precede them. A series of small scale experiments have been conducted burning a timber crib inside an enclosure with tightly controlled ventilation. Under certain fire conditions, the compartment will suddenly erupt, ejecting smoke and flames from the small openings in the compartment. This paper describes the experimental results from the smoke explosion research and compares the smoke explosion to the more familiar phenomena known as backdraft.

Study on the Influence of Window Glass Ignition Temperature on the Heat Release Rate of CRH Passenger Rail Car

The window glass ignition temperature is one of the main factors that determine the Heat Release Rate (HRR) of passenger rail car. In order to reveal the influence of window glass ignition temperature on the HRR of China Railways High-speed (CRH) passenger rail car, the HRR, ignition temperature and other thermal parameters of the individual materials and component assemblies of the CRH passenger rail car, are measured with the Cone Calorimeter, burning temperature tester and other instruments, as the input parameters of Fire Dynamics Simulator (FDS), and according to the different window glass ignition temperatures ,4 fire scenarios have been designed to obtain the HRR vs. time curves of CRH passenger rail car. The comparison results show that the window glass ignition temperature exerts a significant influence on the HRR of passenger rail car; if the ignition temperature is lower than 415°C, during the fire process the windows near the ignition source will be broken, and the back draft phenomenon will take place, resulting in the extremely high second peak HRR, about 22.6MW; if the ignition temperature is higher than 470°C, during the fire process all the windows will not be broken; and so it is suggested that the window glass ignition temperature in the passenger rail car should be higher than 520°C.

Prediction of Cotton Ring Yarn Evenness Properties from Process Parameters by Using Artificial Neural Network and Multiple Regression Analysis

The artificial neural network and multiple regression models have been developed to predict the evenness of cotton ring yarn with process parameters such as front roller speed, spindle speed, nip gauge, back draft zone time and roving twist. The efficiencies of prediction of the two models have been experimentally verified, and the predicted evennesses of cotton ring yarns from both the models have been compared statistically. An attempt has been made to study the effect of process parameters on yarn evenness. The MSE and mean absolute error of ANN modelare lower than that of multiple regression model. The results show that the performances of prediction of ANN models are more accurate than those of multiple regression models.

Drafting Force Forecasting Using Genetic Programming

Genetic programming was used to find out a mathematical model for drafting force from drafting process parameters on the drawing frame, which fits the experimental data as much as possible. The study used rayon fibers as the raw material in the mini-draw frame. The process parameters on the draw frame such as front roller speed, front roller draft, back roller speed and back roller draft as variables were investigated. The paper used the principle that there is linear relationship between drafting force and deformation from the strain gauges in the sensor. The data obtained from online measurement device was used for training and testing on the genetic programming. A comparison between experimental and predicted data was done. The results show very good agreement between the experimental and predicted values. Furthermore, this article shows that genetic programming can provide further use for setting up the machine process parameters without requiring an expert in the field.

An Improved Process Design for the Hot Backward Extrusion of Ti-6Al-4V Tubes Using a Finite Element Method and Continuum Instability Criterion

The hot backward extrusion process of Ti-6Al-4V tubes was designed by finite element (FE) simulation and experimental validations. In the hot backward extrusion of Ti-6Al-4V alloy, the main problems to emerge were surface cracks and sticking between the punch and the workpiece. The punch designs and back draft angles were investigated with a common hot backward extrusion condition. Then, based on a relatively good die design, the optimum process conditions were suggested. The design criteria were to achieve uniform distributions of strain and temperature and to produce a defect-free final product. As a model for predicting the forming defects, the continuum instability criterion developed by Ziegler was coupled to the internal variables generated from FEM simulation. Experimental observations were carried out on the extruded Ti-6Al-4V tubes to validate the model for predicting the forming defects. The die-chilling and friction greatly influenced the deformation mode of the tube and the formation of surface cracks. The formation of defects in the extruded tube was attributed to the non-uniform distribution of strain, strain rate, and temperature in the extruded tubes at the given experiment conditions.

How Distribution of Fibers in the Drafting Zone Affects Drafting Force and Yarn of Cotton/Polyester Blends

Roving drafting force is related to fiber compactness between two drafting aprons. Presented herein is a mathematical model describing the fiber compactness as an index in terms of spinning back draft, residual roving twist, Micronaire value of the cotton/polyester blend, and apron thickness. The effects of fiber compactness on yarn properties and end breakage in spinning are also discussed.

Draft Allocation and Tensor Setting in a Sliver-to-Yarn Drafting System for Cotton

This work investigates the effect of draft allocation on yarn properties in a sliver-to varn drafting system consisting of a back draft zone, an intermediate condensing zone, and a final draft zone. Back and front zones were of the double apron type. The effect of a range of pin openings for the front apron nip was also investigated. Results showed that for optimum yarn properties, back draft D1 and total draft D should be related to each other so that D1 = K √D, where K is a parameter dependent on drafting efficiency and is close to unity. Optimum yarn properties were obtained with the smallest available tensor in the front zone. Finally, in an attempt to explain results on the basis of previous theoretical work by other writers, it was shown that for ideal conditions D1 = √D.