Through the heat-mass transfer analogy, naphthalene sublimation experiments were conducted in a heated-air wind tunnel to study the effects of aspect ratio and dimensionless separation distance on the convective heat transfer coefficients of three tandem naphthalene cylinders. Nusselt number correlations were presented for the individual naphthalene cylinders and the full configuration of three cylinders. In all the cases studied, the Reynolds number had the strongest effect on the Nusselt number followed by the aspect ratio and the dimensionless separation distance. Nusselt numbers were higher for the smaller aspect ratios. For a given Reynolds number and aspect ratio, the Nusselt number increases with the dimensionless separation distance.

Recent experiments show that strong vortices, similar to fire whirls, can form far from a fire front in the region of smoldering fuel. These buoyancy-induced columnar vortices, visualized by entrained smolder smoke, were observed lofting hot embers into the air and in some cases lead to spot ignitions at the base of the vortex. Gaining insight on how the flow field of a buoyancy-induced columnar vortex could impact surrounding smoldering fuel is the focus of this study. Specifically, the potential air entrainment into a fuel substrate beneath the vortex. The flow field of such columnar vortices has been shown to drive air flow downward under certain conditions and, in the context of combustion, drive air deeper than typical entrainment, inducing spot ignitions and increasing burning and smolder rates. NIST's Fire Dynamics Simulator is utilized to successfully model buoyancy-induced columnar vortices. Then it is utilized to study the behavior of vortices as temperature and vorticity boundary conditions are changed. The flow field and fresh air entrainment potential are analyzed. The simulation results inform the experiment design and preliminary experimental results are presented. Understanding these high-risk phenomena will lead to better risk mitigation and more resilient Wildland-Urban interface communities.

Previous studies have shown that most structure ignitions in wildland urban-interface fires are due to firebrand deposition and ignition. The heat transfer mechanisms involved in firebrand deposition need further study and characterization for better understanding of the firebrand ignition process. In particular, convective heat transfer correlations over a single firebrand and a pile of firebrands are lacking. Using the heat-mass transfer analogy, naphthalene sublimation experiments were conducted to determine convective heat transfer correlations for a single naphthalene cylinder (a surrogate firebrand) and an idealized three-firebrand pile resting on flat plates from mass loss measurements. These experiments were conducted in a wind tunnel using a heated (50 °C) or room temperature air flow (0.5 m/s to 2.1 m/s). There was good agreement between the Nusselt number correlation obtained using heated air and results with unheated airflows. Experiments using heated airflow reduced the experimental run times and uncertainty in mass loss measurements significantly. In general, the single firebrand had higher Nusselt numbers than the individual firebrands in the pile. In the three-firebrand pile, the firebrand at the top of the pile exhibited the highest heat transfer. The naphthalene sublimation technique can be easily extended to obtain convective heat transfer correlations for various firebrand geometries and configurations.

While the impact of wildland-urban interface fires is growing, firebrand exposure is a significant but not well understood contributor to fire spread. The ignition threat of firebrand exposures can be characterized by measuring the heat transfer of glowing firebrands to a surface. The current study presents a novel method for conducting time-resolved heat transfer measurements from individual firebrands across a range of flow conditions. Experiments are conducted with individual glowing firebrands generated from birch discs and placed on a copper thin skin calorimeter of the same diameter, which is embedded in the substrate. The net heat flux from the firebrand to the thin skin calorimeter is obtained from the thermal energy storage in the thin skin calorimeter, plus heat conduction losses to the substrate. Values of peak net heat flux, total heating, duration of heating are reported under different flow conditions from 0.05 m/s to 1.6 m/s. The average peak net heat flux for the disc-shaped birch firebrands is 45 kW/m, and does not change significantly with flow condition. However, there is an increase in the total heating, duration of heating, and total mass consumed as the flow velocity increases.

Light Detection and Ranging (LiDAR) is a powerful tool to characterize and track the surface geometry of solid objects. In a fire, however, no method has excelled at measuring three-dimensional shapes at millimeter precision while offering some immunity to the effects of flames. This paper applies coherent Frequency Modulated Continuous Wave Light Detection and Ranging to capture three-dimensional measurements of objects in fire at meters of stand-off distance. We demonstrate that despite the presence of natural gas flame depths up to 1.5 m obscuring the target, measurements with millimeter precision can be obtained. This is a significant improvement over previous work making the technique useful for many fire research applications. An approach to achieve sub-millimeter precision using spatial and temporal averaging during post-processing is presented. The technology is demonstrated in case studies of structural connection and vegetation response in fires.

Research was conducted to examine the use of Support Vector Regression (SVR) to build a model to forecast the potential occurrence of flashover in a single-floor, multi-room compartment fire. Synthetic temperature data for heat detectors in different rooms were generated, 1000 simulation cases are considered, and a total of 8 million data points are utilized for model development. An operating temperature limitation is placed on heat detectors where they fail at a fixed exposure temperature of 150 °C and no longer provide data to more closely follow actual performance. The forecast model P-Flash (Prediction model for Flashover occurrence) is developed to use an array of heat detector temperature data, including in adjacent spaces, to recover temperature data from the room of fire origin and predict potential for flashover. Two special treatments, sequence segmentation and learning from fitting, are proposed to overcome the temperature limitation of heat detectors in real-life fire scenarios and to enhance prediction capabilities to determine if the flashover condition is met even with situations where there is no temperature data from all detectors. Experimental evaluation shows that P-Flash offers reliable prediction. The model performance is approximately 83 % and 81 %, respectively, for current and future flashover occurrence, considering heat detector failure at 150 °C. Results demonstrate that P-Flash, a new data-driven model, has potential to provide fire fighters real-time, trustworthy, and actionable information to enhance situational awareness, operational effectiveness, and safety for firefighting.

This paper presents a study to examine the potential use of machine learning models to build a real-time detection algorithm for prevention of kitchen cooktop fires. Sixteen sets of time-dependent sensor signals were obtained from 60 normal/ignition cooking experiments. A total of 200 000 data instances are documented and analyzed. The raw data are preprocessed. Selected features are generated for time series data focusing on real-time detection applications. Utilizing the leave-one-out cross validation method, three machine learning models are built and tested. Parametric studies are carried out to understand the diversity, volume, and tendency of the data. Given the current dataset, the detection algorithm based on Support Vector Machine (SVM) provides the most reliable prediction (with an overall accuracy of 96.9 %) on pre-ignition conditions. Analyses indicate that using a multi-step approach can further improve overall prediction accuracy. The development of an accurate detection algorithm can provide reliable feedback to intercept ignition of unattended cooking and help reduce fire losses.

Several series of measurements were made to characterize medium-scale pool fires steadily burning in a well-ventilated, quiescent, open environment. Time-averaged local measurements of radiative and total heat flux were made in steadily burning methyl alcohol (methanol; CHOH), ethyl alcohol (ethanol; CHOH), and acetone ((CH) CO) pool fires. The fuel lip height in a water-cooled stainless-steel burner was maintained at 10 mm. Schmidt-Boelter heat flux gauges were used to measure the radiative emission to the surroundings. The total heat flux directed towards the pool surface was measured using a Gardon gauge positioned just above the pool surface. A previously developed method was used to calculate the convective heat flux to the pool surface, allowing estimation of the radiative flux, which agreed within experimental uncertainty with a previous measurement in the methanol pool fire. The steady-state mass burning rate was measured using a load cell, and the heat release rate was measured in the exhaust using calorimetry. The energy balance for each of the fires was determined. The results showed that both radiation and convection play significant roles in these pool fires. Radiation was the dominant mechanism of heat feedback to the fuel surface, accounting from 68 % to 88 % of the energy, while enthalpy convected in the plume represented 68 % to 78 % of the fire's total energy, far exceeding radiative emission to the surroundings.

This paper presents a systematic investigation of the influence of various parameters on the thermal performance of composite floor slabs with profiled steel decking exposed to fire effects. The investigation uses a detailed finite-element modeling approach that represents the concrete slab with solid elements and the steel decking with shell elements. After validating the modeling approach against experimental data, a parametric study is conducted to investigate the influence of thermal boundary conditions, thermal properties of concrete, and slab geometry on the temperature distribution within composite slabs. The results show that the fire resistance of composite slabs, according to the thermal insulation criterion, is generally governed by the maximum temperature occurring at the unexposed surface of the slab, rather than the average temperature. The emissivity of steel has a significant influence on the temperature distribution in composite slabs. A new temperature-dependent emissivity is proposed for the steel decking to give a better prediction of temperatures in the slab. The moisture content of the concrete has a significant influence on the temperature distribution, with an increment of 1 % in moisture content leading to an increase in the fire resistance of about 5 minutes. The height of the upper continuous portion of the slab is found to be the key geometrical factor influencing heat transfer through the slab, particularly for the thin portion of the slab. Heat transfer through the thick portion of the slab is also significantly affected by the height of the rib and the width at the top of the rib.

The behavior of high-strength structural steel at elevated temperatures, especially under shear loading, is not well established in the literature. This paper presents results from recently conducted tests on high-strength structural bolts subject to double shear loading at elevated temperatures. The parameters varied between tests included the bolt grade, bolt diameter, and temperature. Bolt grades A325 and A490 were tested. For each bolt grade, three different diameters were tested (19 mm (3/4 in), 22 mm (7/8 in), and 25.4 mm (1 in)) at five different temperatures (20 °C, 200 °C, 400 °C, 500 °C, and 600 °C). At least three tests were conducted for each combination of parameters. Degradations in the mechanical and material properties including stiffness, strength, and deformation at fracture, are characterized and presented herein. The results from these experiments fill a critical knowledge gap currently present in the literature regarding the behavior of high-strength structural bolts under shear loading at elevated temperatures. These data will ultimately provide a thorough understanding of the overall behavior of structural steel systems under realistic fire loading by clarifying the (i) shear behavior of high-strength structural steel bolts at elevated temperatures, and (ii) degradation in the mechanical and material properties of high-strength steel bolts with increasing temperatures.

A series of tests was conducted on six 2.7 m × 3.7 m shear wall specimens consisting of cold-formed steel framing sheathed on one side with sheet steel adhered to gypsum board and on the opposite side with plain gypsum board. The specimens were subjected to various sequences of simulated seismic shear deformation and fire exposure to study the influence of multi-hazard interactions on the lateral load resistance of the walls. The test program was designed to complement a parallel effort at the University of California, San Diego to investigate a six-story building subjected to earthquakes and fires. The test results reported here indicate that the fire exposure caused a shift in the failure mode of the walls from local buckling of the sheet steel in cases without fire exposure, to global buckling of the sheet steel with an accompanying 35 % reduction in lateral load capacity after the wall had been exposed to fire. This behavior appears to be predictable, which is encouraging from the standpoint of residual lateral load capacity under these severe multi-hazard actions.

This paper discusses the development of a finite element (FE) model of a full-scale composite floor system and application of this model to predict the heating of steel members when exposed to a standard fire during fire resistance experiments. The model is verified by comparing the predicted heating profile of steel members at several locations during the tests with measured data. Such a verified model can be used to characterize the uncertainties in the prediction of the thermal history of structural elements exposed to a damaging fire. The output of this model can be used in a subsequent structural analysis model to determine the nonlinear behavior of structural members due to both thermal and mechanical loads. Additionally, the thermal effect of possible concrete spalling events and the resultant fireproofing dislodgement from steel members were numerically investigated and compared with measured data to determine the efficacy of the heat transfer model.

Large outdoor fires present a risk to the built environment. Wildfires that spread into communities, referred to as Wildland-Urban Interface (WUI) fires, have destroyed communities throughout the world, and are an emerging problem in fire safety science. Other examples are large urban fires including those that have occurred after earthquakes. Research into large outdoor fires, and how to potentially mitigate the loss of structures in such fires, lags other areas of fire safety science research. At the same time, common characteristics between fire spread in WUI fires and urban fires have not been fully exploited. In this paper, an overview of the large outdoor fire risk to the built environment from each region is presented. Critical research needs for this problem in the context of are provided. The present paper seeks to develop the foundation for an international research needs roadmap to reduce the risk of large outdoor fires to the built environment.

This study explores an instrumentation strategy using distributed fiber optic sensors to measure strain and temperature through the concrete volume in large-scale structures. Single-mode optical fibers were deployed in three 12.8 m long steel and concrete composite floor specimens tested under mechanical or combined mechanical and fire loading. The concrete slab in each specimen was instrumented with five strain and temperature fiber optic sensors along the centerline of the slab to determine the variation of the measurands through the depth of the concrete. Two additional fiber optic temperature sensors were arranged in a zigzag pattern at mid-depth in the concrete to map the horizontal spatial temperature distribution across each slab. Pulse pre-pump Brillouin optical time domain analysis (PPP-BOTDA) was used to determine strains and temperatures at thousands of locations at time intervals of a few minutes. Comparisons with co-located strain gauges and theoretical calculations indicate good agreement in overall spatial distribution along the length of the beam tested at ambient temperature, while the fiber optic sensors additionally capture strain fluctuations associated with local geometric variations in the specimen. Strain measurements with the distributed fiber optic sensors at elevated temperatures were unsuccessful. Comparisons with co-located thermocouples show that while the increased spatial resolution provides new insights about temperature phenomena, challenges for local temperature measurements were encountered during this first attempt at application to large-scale specimens.

This paper provides a report of the discussions held at the first workshop on Measurement and Computation of Fire Phenomena (MaCFP) on June 10-11 2017. The first MaCFP work-shop was both a technical meeting for the gas phase subgroup and a planning meeting for the condensed phase subgroup. The gas phase subgroup reported on a first suite of experimental- computational comparisons corresponding to an initial list of target experiments. The initial list of target experiments identifies a series of benchmark configurations with databases deemed suitable for validation of fire models based on a Computational Fluid Dynamics approach. The simulations presented at the first MaCFP workshop feature fine grid resolution at the millimeter- or centimeter- scale: these simulations allow an evaluation of the performance of fire models under high-resolution conditions in which the impact of numerical errors is reduced and many of the discrepancies between experimental data and computational results may be attributed to modeling errors. The experimental-computational comparisons are archived on the MaCFP repository [1]. Furthermore, the condensed phase subgroup presented a review of the main issues associated with measurements and modeling of pyrolysis phenomena. Overall, the first workshop provided an illustration of the potential of MaCFP in providing a response to the general need for greater levels of integration and coordination in fire research, and specifically to the particular needs of model validation.

In the interest of fire prevention, most materials used in the interior construction of manned spacecraft are non-flammable, however, they do produce smoke when overheated. Spacecraft smoke detectors will ideally detect smoke generated by oxidative pyrolysis (such as smoldering) in order to allow the maximum time for the crew to respond before a larger flaming fire develops. An experiment on the International Space Station (ISS) characterized smoke from overheating common spacecraft materials. The following parameters were controlled: heating temperature, air flow past the samples and duration of aging. Two different spacecraft smoke detectors were included in the instrumentation and their performance with different smoke types has been evaluated. Additional equipment in the experiment included a thermal precipitator to sample particles for microscopic analysis upon return to Earth, and three commercial-off-the-shelf real-time instruments to measure particle mass and number concentration, and an ionization detector calibrated to estimate the first moment of the size distribution. Results from the ISS experiment show that smoke particles vary in morphology and average diameter, however, they are not significantly different from smoke particles generated in equivalent experiments performed in normal gravity. The two spacecraft smoke detectors did not successfully detect every type of smoke, which demonstrates that the next generation of spacecraft fire detectors must be improved and tested against smoke from relevant space materials.

The response of structural systems to fire loads is typically assessed through performing 'standard' fire tests on individual members under constant mechanical boundary conditions. Full scale tests showed different behavior compared to the standard tests, but remain impractical. A promising approach to predict the behavior of full scale tests through testing individual structural members is Hybrid Fire Testing technique, where a subset of the structural system (Physical Substructure PS), is physically tested, while the remaining structure (Numerical Substructure NS), is simultaneously numerically analyzed. During the test, the mechanical boundary conditions on the PS and NS are continuously updated, and the updates are enabled by the communication framework. The communication framework is a key element for a successful hybrid fire testing and this paper will present the development of such communication in MATLAB. To validate the communication framework, first, a single degree of freedom linear system was analyzed, followed by a ten-story steel frame structure exposed to design fire. The analysis of the latter underlined the importance of considering the effect of the cold surrounding in assessing the fire behavior of structures under design fires. Sensitivity analysis showed the importance of several parameters (time step and substructures stiffness) in hybrid fire testing.

As part of recent building code change discussions, it has been suggested that by increasing the spacing of boards, it may be possible to mitigate ignition of wood decking assemblies from wind-driven firebrand showers. An experimental series was undertaken to vary the board spacing from 0 mm (no gaps), 5 mm, and 10 mm, to determine if it was possible to observe reduced ignition propensity of full-scale wood decking assemblies fitted to a reentrant corner wall assembly. In these experiments, three common wood types were used and firebrand showers were directed at the wall/decking assemblies using wind speeds of 8 m/s generated using a realistic-scale wind tunnel. Based on the results of these experiments, it was observed that board spacing significantly influenced ignition propensity of these assemblies. Ignition events were observed for all board spacing considered and in particular, more ignition points were observed for a board spacing of 10 mm.

Structures fitted with thatched roofing assemblies are prone to ignition during the course of large outdoor fires. Experiments with thatched roofing assemblies were performed by using a reduced-scale continuous-feed firebrand generator in a wind facility to investigate fundamental ignition mechanisms. The wind speed was varied from 3 m/s to 6 m/s to observe the ignition and flame spread of thatched roofing assemblies. It was observed that firebrands penetrated into the thatched roofing assembly, sometimes unseen from the outside, resulting in ignition and ultimately rapid flame penetration. Information obtained in this study would be useful to evaluate and develop effective counter measures to protect historical structures with thatched roofing assemblies, especially for historical buildings, such as The United Nations Educational, Scientific and Cultural Organization (UNESCO)'s world heritage sites in Japan.

360-degree video recorded in fires provides a unique perspective that allows the viewer to change the viewing direction as regions of interest change during a fire. Use of 360-degree and traditional cameras at some locations in intense fires for extended durations has been hampered in the past by the high levels of radiant heat flux that will damage the camera's imaging sensor. This paper describes how a thin layer of moving water can be used to significantly reduce unwanted infrared radiation generated by a fire while allowing visual imaging using a simple and inexpensive enclosure. Essential details to replicate this system are provided and three illustrative example deployments are discussed.