In order to investigate the effects of the humidity, temperature and slow oxidation reactions on the occurrence of explosions in gasoline-air mixtures, experiments are carried out in a cylindrical tunnel with a solid heating device. Experimental results show that whether a gasoline-air explosion occurs or not is determined by a critical relative humidity when the temperature of the heat source is maintained at a specific value. Under the experimental conditions in this study, when the heat source temperature is maintained at 550?, the critical value of relative humidity is 32.3%+/- 0.2%, and when the heat source temperature is maintained at 570?, the critical value of relative humidity climbs to 37.7%+/- 0.2%. The occurrence of gasoline-air explosions is very sensitive to the gas mixture temperature. It is shown that an explosion will not occur if the gas mixture temperature is lower than the critical value of 26?. Influenced by slow oxidation reactions, concentrations of reactants can decrease below the explosion limit range, resulting sometimes in no observed occurrence of gasoline-air explosions. Experiments show, in this case, that the critical heat source temperature for the gas mixture explosion, defined by a probability of explosion occurrence of 20%, climbs from 510 to 550?, i.e. it increases 40? solely due to the influence of slow oxidation reactions.
In a transportation hub complex (THC) in China, ticket entrance gates and station exits are common bottlenecks. Although road traffic in China follows right-hand traffic rules, the influence of right-hand traffic rules on the movement characteristics of pedestrians passing through such facility bottlenecks have been investigated rarely. In this article, simulation experiments are conducted to investigate the effect of THC bottle-necks on pedestrian movement characteristics given the existence of right-hand road traffic rules. Based on the use of a combination of histograms of oriented gradients and support vector machine algorithms, the movement behavior of pedestrians passing through multiple parallel bottlenecks are extracted. A total of 21 scenarios are considered in this simulation experiment, consisting of two-opening and three-opening parallel bottlenecks, where the width of each opening and width of the barriers between adjacent openings are varied. This study provides fundamental data for pedestrian flow passing through multiple parallel bottlenecks, data that can help identify important parameters for the design and improvement of many kinds of pedestrian flow management facilities. Results from the study also will be useful for the development and verification of evacuation models.
Based on the Froude-modeling scaling approach, water mist protection for a 7.47x7.47x7.47-m cut-off room where ignitable liquids are used was projected from the previously determined extinguishing requirement for heptane pool fires in a 1/2-scale enclosure and then verified with full-scale testing. The full-scale building occupancy was required to accommodate cut-off room door openings ranging from 1.86x3.73m high up to 3.73x3.73m. The fire challenge was a heptane spill fire cascading from the top of a 1.83-m dia. by 2.74-m high steel tank at a spill rate of 37.9L/min. Two off-the-shelf nozzles were selected as candidates for the full-scale building to approximate the scaled-up water mist spray requirement. At a discharge pressure of 90bar, one nozzle discharged 28L/min, with a spray angle of 100 degrees and a volume-median droplet dia. of 115 mu m; the other discharged 24.4L/min, with a 180 degrees spray angle and median dia. of 96 mu m. Nine nozzles were arranged at the ceiling level in a 3x3 matrix with a spacing of 1.86x1.86m. Before the two candidate protection schemes were challenged with the spill fire, scaled-up heptane pool fires were used to ensure that the fire extinguishing propensity was consistent with that observed in the 1/2-scale enclosure. The pool fire tests showed that the nozzle with the smaller spray angle provided better fire extinguishing performance, which was later confirmed in the spill fire tests. The protection scheme with the smaller spray angle could extinguish the spill fire for door openings up to 3.05x3.05m. For larger openings, two additional downward water mist sprays were required in the door opening to expedite fire extinguishment by reducing ventilation through the door opening. Water mist protection could provide adequate cooling to fuel tanks as long as such protection could extinguish the fire. Overall, the investigation demonstrated that physical scaling is a useful tool to provide an engineering estimate of water mist protection requirements.
Traditionally, the only parameter used to measure the performance of total compartment (i.e. total flooding) water mist or water spray systems during fire testing has been the time to extinguishment. However, the use of a single parameter has been criticized since it can result in poor system designs. This study evaluates additional parameters in order to improve the characterization of system performance. Two series of fire tests were conducted with a number of water mist and water spray fire protection systems: the former in a 500m(3) test compartment using three different systems; the latter in a 250m(3) compartment using four different systems. The heat release rate of the fire and the gas temperatures inside the test compartment were measured. Based on these measurements, the fire suppression capability of the systems, their temperature reduction capability and their ability to mix water vapor, water droplets and combustion gases within the compartment were determined. The tests revealed that the time to extinguishment varies several tens of percent under identical conditions. It was also observed that the relative performance of the systems was influenced by the size of the fire. The results obtained with the additional parameters were much more repeatable and consistent than using time to extinguishment alone. It is concluded that fairly simple and inexpensive measurements can improve current fire test procedures.
A numerical model for the behavior of concrete slabs in a fire is described. This model consists of a shell finite element, a damage constitutive model for concrete with steel reinforcement and the consideration of heat transfer through the thickness of the slab. An improved damage constitutive model for concrete at elevated temperatures has been implemented considering compressive and tensile behavior through an orthotropic compliance theory. The damage in compression is based on the concrete stress-strain relationships presented by the European Committee for Standardization. Several calculations have been performed to validate the improved model. The comparison with experimental tests and numerical results confirm the validity of the approach for reinforced concrete slabs subjected to large transverse displacement.
The use of antifreeze in water mist fire suppression systems offers a potential alternative to the current applications of these systems in subfreezing environments. Design and development of these systems, however, requires quantitative data detailing the effect of antifreeze on factors, such as small droplet sizes and/or higher system pressures which is currently unavailable. This study investigates the use of antifreeze, of various chemical compositions and concentrations, in water mist systems by quantifying variables that affect spray characteristics, indicate the potential risk of system failure, and evaluate the interactions of the discharged agent with the fire. Extensive testing and analysis demonstrate that no tested antifreeze solution behaves ideally with respect to quantified variables. Some of the antifreezes tested should not be used above a certain concentration in high-pressure water mist systems due to solution flammability and the resulting contribution to the heat release rate of the fire. The impact of all other tested pressure and concentration combinations is less significant on the heat release rate of the fire. Therefore, solutions used at these respective pressures and concentrations are potentially suitable for use in water mist systems unless spray performance or the potential risk of system failure discourages their use. Ignitibility of the antifreeze discharge was proven to be a function of antifreeze solution concentration and droplet size. Future testing should determine the threshold droplet size for ignition of the antifreeze discharge and at what point changes in solution properties begin to significantly impact droplet size in subfreezing environments.
This paper describes the occupant evacuation of World Trade Center (WTC) 1 and WTC 2 on September 11, 2001. Multiple sources of information were collected and analyzed: over 1,000 new interviews with survivors (including 803 telephone interviews, 225 face-to-face interviews, and 6 focus groups); over 700 published interviews; 9-1-1 emergency calls; transcripts of emergency communications, historical building design drawings, memoranda, and calculations; formal complaints filed with the Occupational Safety and Health Administration; and other relevant materials. The population in WTC 1 and WTC 2 on September 11, 2001, at 8:46:30 a.m. is enumerated and described, where the characteristics of the population were relevant to the subsequent evacuation, including training, experience, mobility status, among others. The progress of the evacuation of both towers is described in a quasi-chronological manner from 8:46:30 a.m. when WTC 1 was attacked, until 10:28:22 a.m., when WTC 1 collapsed.
The objective of this study is to investigate the effect of temperature distribution, concrete strength, cover thickness, and heating time on the structural behavior of reinforced concrete beams. Toward this goal, reinforced concrete beams with different concrete compressive strength and cover thickness are fabricated and subjected to furnace heating for 60, 90, and 120 min under a loaded state. In order to analyze structural behavior based on the thermal behavior of the beams, transient temperature distribution is measured during the furnace heating. After furnace heating, spalling is observed. From loading tests performed on the damaged reinforced concrete beams, residual strength, maximum loads, and beam deflections are measured and examined. The experimental results show that significant damage occurs in the reinforced concrete beams under high temperatures. In addition, it is found that thermal and structural behavior of damaged reinforced concrete beams is dependent on cover thickness and concrete strength and that most structural damage occurs in a relatively short period of heating time. Using these experimental findings, an equation is proposed that can be used to predict maximum load capacity and stiffness reduction ratio of the damaged reinforced concrete beams.
The major factors that impact residential fire losses and casualties are relatively well known both on the national level and for any given state. Interestingly, relatively little has been done in comparing fire loss data between states. If state fire loss data are compared, one should be able to identify contributing factors that influence differences in fire losses between states. As an example, it is known that construction standards, regulatory policy, socio-economic factors, etc. all influence the frequency and severity of fires. In this study, subsets of National Fire Incident Reporting System (NFIRS) data for the two largest US states by population are studied in order to identify how areas of origin, items first ignited, and heat sources contribute to the odds of casualties or fatalities occurring in fires, as well as to examine differences between the two states for these three factors. Data on residential home fires from 2006 to 2010 were gathered from the Texas and California NFIRS databases, Texas Fire Incident Reporting System and California All Incident Reporting System, respectively, for this purpose. Examination of the datasets separately using logistic regression models emphasized that fires started in the living room or den, fires in which the item first ignited was a flammable liquid, piping, or filter, and fires that were initiated from cigarettes, pipes, and cigars, all have significantly high odds of resulting in both casualties and fatalities for both states. Additionally, logistic regression modeling with interactions between state and area of origin, item first ignited, and heat source indicated that for many categories, the odds of a fire resulting in a casualty in Texas is roughly 1.5 times higher than the same fire in California.
A review of two decades of worldwide experience using standards, codes and guidelines related to performance-based fire protection design for buildings has identified shortcomings in the interpretation, application and implementation of the performance-based design process, apparent inconsistency in the resulting levels of performance achieved and several opportunities to enhance the process. In a constantly evolving building environment, technical challenges have to be overcome because fire safety engineering still depends greatly on knowledge gained from scientific and engineering research across a broad range of disciplines (e.g., better understanding of the fire phenomena, the behavior and response of the building occupants/contents/structure to the fire, tools for engineering analysis and all the necessary data needed to support tool application). Political challenges also need to be considered as performance-based fire protection design requires the approval of the authority having jurisdiction and other involved stakeholders, at several of its different steps (design, construction, original usage, modifications of usage). The review presented here has been undertaken from an engineering perspective rather than a regulatory perspective. Two key outcomes of this engineering review are that several of the challenges that have been identified are strongly linked to the application of generic guidance to specific problems, which results in critical details being missed, and that some of the engineering issues are treated within a political context, while they should be addressed as purely technical issues.
The purpose of this study was to collect and analyze individual unimpeded stair ascent and descent walk speeds for the Korean population. To collect these data, a full-scale experiment was conducted in a 50-storey residential building in Korea involving 30 male and 30 female participants with an average age of 23.4 years. Each participant was required to ascend 50 floors and after a suitable rest period was then required to descend 50 floors using the stairs. Arrival times on each floor were recorded using video cameras, allowing floor by floor walk speeds to be determined and to assess whether fatigue affected the descent/ascent. The average descent speed for the male and female population was 0.83 m/s and 0.74 m/s, respectively, while the average ascent speed was 0.66 m/s and 0.48 m/s. However, there was no significant relationship between body mass index and stair walk speed or unimpeded horizontal walk speed and stair walk speed. During the descent, 50% of the population displayed a decrease in the walk speed over the final half of the descent with a maximum decrease of some 19%. However, some 50% of the population increased their travel speed during the final half of the descent. During the ascent, all participants decreased their speed over the first 20 floors by an average of approximately 60%. Implications of these findings for evacuation modeling/simulation are discussed.
A series of fire tests was conducted involving a 2.44-m-(8-ft)-diameter, 4.57-m-(15-ft)-long, 2.54-cm-(1-inch)-wall thickness pipe calorimeter suspended 1-m above a 7.93-m-diameter pool that contained 7.57 m3 (2000 gallons) of jet fuel. The wind conditions, calorimeter temperature, participating media temperature and speed, and radiant heat flux, were measured at several locations as functions of time in three fire tests. The first two had relatively light winds and lasted roughly 40 minutes, while the third had much stronger winds and consumed the fuel in 25 minutes. The purpose of this paper is to describe the experimental facilities and certain fire characteristics. The large amount of data acquired cannot be fully presented in this paper. A website is available by contacting the first author so that the full data set may be used to quantitatively benchmark large-fire simulations and models.
A review of the literature has shown the need for a comprehensive flame spread dataset framework for computational fluid dynamics model validation purposes. To develop this framework, the flame spread process was viewed as having four key components: turbulent fluid dynamics, gas phase kinetics, flame heat transfer, and condensed-phase pyrolysis. A series of extensively instrumented inter-related experiments based on the four components was conducted under different source fire permutations. This series of three progressively more complex experiments, from free plume, to inert wall fires, to combustible wall flame spread were carried out to enable collection of data relevant to each component of flame spread. Measurements made include heat release rate, plume centerline temperature and velocity, heat flux to wall, near-wall temperature, flame height, flame spread progression, mass loss, and burn pattern. The combustible wall test data in the current research may not be enough to validate a complex real-wo...
In order to deal with uncertainties in evacuation time associated with the uncertainty in input parameters at a reasonable computational cost, a probabilistic method based on polynomial chaos expansion is proposed that combines evacuation models with Latin hypercube sampling. Evacuation models enable the prediction of evacuation time; polynomial chaos expansion is used to construct a surrogate model of evacuation time; Latin hypercube sampling is adopted as post-processing of the surrogate model to predict numerically the distribution of evacuation times. Additionally, an Uncertainty Factor is defined to quantify the total effect of the uncertainty of input parameters on evacuation time. To illustrate the proposed probabilistic method, evacuation of a simplified fire compartment typical of large commercial buildings is analyzed while considering uncertain input parameters including occupant density, child-occupant load ratio and exit width. This case study indicates that when exit width is small, the Uncertainty Factor is almost constant with respect to exit width but increases with an increase in specified (acceptable) reliability level. Furthermore, if exit width exceeds a certain critical value, the Uncertainty Factor will decrease with an increase in exit width and its sensitivity to reliability level will become smaller. Finally, the case study shows that compared with the conventional Monte Carlo simulation, the proposed method can give similar estimations of evacuation time uncertainty at a significantly reduced computational cost.
Available safe egress time is an important criterion to determine occupant safety in performance-based fire protection design of buildings. There are many factors affecting the calculation of available safe egress time, such as heat release rate, smoke toxicity and the geometry of the building. Heat release rate is the most critical factor. Due to the variation of fuel layout, initial ignition location and many other factors, significant uncertainties are associated with heat release rate. Traditionally, fire safety engineers prefer to ignore these uncertainties, and a fixed value of heat release rate is assigned based on experience. This makes the available safe egress time results subjective. To quantify the effect of uncertainties in heat release rate on available safe egress time, a Monte Carlo simulation approach is implemented for a case study of a single hypothetical fire compartment in a commercial building. First, the effect of deterministic peak heat release rate and fire growth rate on the predicted available safe egress time is studied. Then, the effect of uncertainties in peak heat release rate and fire growth rate are analyzed separately. Normal and log-normal distributions are employed to characterize peak heat release rate and fire growth rate, respectively. Finally, the effect of uncertainties in both peak heat release rate and fire growth rate on available safe egress time are analyzed. Illustrations are also provided on how to utilize probabilistic functions, such as the cumulative density function and complementary cumulative distribution function, to help fire safety engineers develop proper design fires.
In performance-based analyses, engineers evaluate whether a building design and/or evacuation procedure allows occupants sufficient time to evacuate before fire conditions become untenable. Guidance exists for the calculation of the time until conditions become untenable in areas of the structure (known as the available safe egress time) during fire situations. This article presents a method for determining the amount of time required for building occupants to reach a defined point of safety (known as the required safe egress time) for a particular building design or scenario. The method requires the engineer to identify real-world factors from the building conditions/situations that influence human performance (e.g. evacuation), understand the nature of their impact on human performance and then represent this impact in terms that can be employed within evacuation model calculations. An example is also presented to demonstrate the method described here.
The fire floor of a hotel fire that resulted in serious casualties in Taiwan was reconstructed as the site of a full-scale evacuation test. Health status assessments were conducted on 50 adults between ages of 25 and 75, and then their horizontal movement speed was measured as a function of three physical conditions: normal health, wheelchair bound and on crutches. The 50 subjects were divided into nine groups for three kinds of evacuation strategies in order to measure the evacuation time of each group. In addition, taking into consideration the three aforementioned kinds of physical conditions, 40 of the 50 subjects were organized into six types of conditions to conduct exit width tests by measuring the evacuation time for passing through exits with widths of 0.75 m and 1.2 m. The two kinds of evacuation test results can be used as a reference for improving fire safety strategies for future hotel construction.
In recent years there has been an increased interest in the use of fiber reinforced polymer (FRP) materials in concrete members. However, the behavior of such members in fire is still relatively unknown. Since this is the main reason limiting the widespread use of FRP in buildings, the use of FRP in fire vulnerable structures needs additional study. In this article, a model is developed that incorporates the temperature dependent progressive changes of Elastic-modulus of FRP in predicting the deflection behavior of FRP reinforced concrete structures within the range of practical elevated temperatures. Predictions from the model correlate well with experimental results from the literature. The new approach provides an additional tool to evaluate the deflection of FRP reinforced concrete structures in fire.
