Fire Protection Engineering
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Item HEALTH IMPACTS OF THERMAL RUNAWAY EVENTS IN OUTDOOR LITHIUM-ION BATTERY ENERGY STORAGE SYSTEM INSTALLATIONS(2024) Zhao, Zelda Qijing; McAllister, Jamie; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study aimed to develop a methodology for characterizing health impacts of large-scale, outdoor, lithium-ion battery energy storage systems (BESS) thermal runaway events. A literature review was conducted to identify toxic gas yields produced during flaming and non-flaming thermal runaway, as well as mass loss rates, gas temperature, typical BESS unit capacity and dimensions, and event durations. Lithium-iron-phosphate and nickel-manganese-cobalt cell chemistries were assessed. The BESS unit thermal runaway events were modeled in Fire Dynamics Simulator with a bounding analysis for wind and ambient temperature. Concentrations were evaluated using Immediately Dangerous to Life or Health values for occupational exposure and the Protective Action Criteria for Chemicals hierarchy values (Acute Exposure Guideline Levels- Level 1, Emergency Response Planning Guidelines- Level 1, Temporary Emergency Exposure Limits- Level 1) for community exposure. Through application of the methodology, a relationship between exposure limit distance and wind speed, ambient temperature, event duration, cell chemistry, and toxic gas species can be assessed. Under the conditions modeled in this project, exposure limits were exceeded at longer distances in the non-flaming scenarios when compared to the flaming scenarios. Wind speed, ambient temperature, event duration, cell chemistry, and toxic gas species were the controlling factors for non-flaming exposure limit distances. Wind speed was the primary controlling factor for flaming exposure limit distances; however, event duration had some influence.Item DEVELOPMENT AND VALIDATION OF A PYROLYSIS MODEL FOR FLEXIBLE POLYURETHANE FOAM(2024) Kamma, Siriwipa; Stoliarov, Stanislav I; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Flexible polyurethane foam (FPUF) is a common material contained in household goods such as upholstered furniture and mattresses, which are known to significantly contribute to fire growth. An accurate prediction of fire development on FPUF containing items requires knowledge of FPUF pyrolysis and combustion properties. These properties include reaction kinetic parameters, thermodynamic parameters, and thermal transport properties. While many past studies focused on the thermal decomposing mechanism and thermodynamic properties of the reactions, the thermal transport properties have not been determined. In this study, a complete pyrolysis model of FPUF was developed by extending the thermal decomposition model from a previous study. The thermal transport properties were obtained using inverse modeling of the Controlled Atmosphere Pyrolysis Apparatus II experimental data. The complete model was validated against cone calorimetry data and found to perform in an adequate manner.Item DESIGN AND PERFORMANCE EXPLORATION OF A SCALED-UP MILLIGRAM-SCALE FLAME CALORIMETER(2024) Cromwell Reed, Kyra; Raffan-Montoya, Fernando; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fire causes thousands of lost lives and injuries, as well as billions of dollars of property damage, each year. It is critical to understand the fire hazard associated with materials used in the built environment. One method to evaluate the flammability properties of a material is through bench- scale and milligram-scale testing with apparatus such as the Milligram-Scale Flame Calorimeter (MFC). The MFC has previously been used to test samples ranging from 30 mg – 50 mg in mass. The small samples were useful for testing materials under development or materials cost prohibitive to test at larger sizes, but presented some difficulties in testing, including in sample preparation and as inconsistency in the results of testing on inhomogeneous materials. Furthermore, the small size of the MFC caused difficulty in heater manufacturing, requiring laborious by-hand construction. The size of the MFC crucible and apparatus was increased in this work to allow testing on larger sample masses, ranging in size from 90 mg – 150 mg, and for the exploration of five alternate heater manufacturing techniques. The MFC was rebuilt with a larger heater and optimized to create the best possible test conditions for this work. Tests were conducted on five polymers: polymethyl methacrylate (PMMA), polyethylene (PE), polyvinyl chloride (PVC), and polyether ether ketone (PEEK), and on a wood-based material: oriented strand board (OSB). The tests showed general consistency when materials were tested at different sample masses and sample presentations. The results for the heat release rate and heat of combustion of the materials also aligned well with testing conducted using the previous version of the MFC apparatus. The updates to the MFC conducted in this work constitute an improvement to the versatility of the apparatus, allowing for testing on larger sample masses, but future work is needed to resolve flow and exhaust issues that caused some inconsistency in the test results and to further explore and develop alternate heater manufacturing techniques.Item Experimental Characterization of the Thermal Response of Firefighter Protective Ensembles Under Non-Flaming Convective Exposure(2024) DiPietro, Thomas Phillip; Raffan-Montoya, Fernando; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Thermal burns are one of the most serious injuries a firefighter can sustain while operating in a structure fire despite being fully covered in gear designed to protect them from thermal exposure. Extensive experimentation has been conducted into the performance of a firefighter’s protective ensemble when caught in a high radiative heat flux environment to ensure the wearer has enough time to escape to safety. High heat flux tests are beneficial in estimating safe operating times, but firefighters are also getting burned in fire environments that are thought to be routine exposures. The current study explored the thermal response of three-layer firefighter protective ensembles exposed to a majority convective, low-level heat flux in an oven. Through experimentation, the temperature of a copper calorimeter simulating skin beneath two different protective ensembles were measured while exposed to temperatures of 100°C, 150°C, 200°C, 250°C, and 300°C. The time for the copper calorimeter to reach a temperature of 55°C (the temperature a second-degree burn has the potential to occur to human skin) was recorded and compared to currently accepted thermal operating time limits for firefighters. Results show that once exposure reached above 100°C the time for a potential burn injury to occur fell below the predicted safe operational time for firefighters of 15–20 minutes when the PPE was in contact with the copper disk. The time to potential burn injury and test temperature exhibited an exponentially decaying relationship which is expected to continue as temperatures increase beyond those tested in the current study. Although consisting of different layers of material, both types of protective ensembles tested responded similarly and demonstrated no significant differences in time to potential burn injury at every temperature. Additional tests were conducted in the oven with an air gap placed below the protective ensemble as well as using the original test set up with a mostly radiative heat source to compare results and evaluate different exposures and conditions for future experimentation.Item A study of Cool Diffusion Flames utilizing Ignition Delay Characteristics of N-Heptane Autoignition Simulations(2024) Pimple, Shubham; Sunderland, Peter; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Gaining deeper insights into cool diffusion flames (CDFs) can significantly enhance engine efficiency and reduce emissions, while also filling in knowledge gaps relating to explosion initiation and the transition from smoldering to flaming fires. While detailed computational fluid dynamic (CFD) models can simulate CDFs, they require substantial computational resources due to the need for detailed chemistry and transport resolution. To circumvent these challenges, this study utilizes an alternative approach using Cantera autoignition simulations, which presumes isobaric, adiabatic conditions. The fuel, n-heptane, is analyzed through six kinetic mechanisms that capture the spectrum of low and high temperature chemistry. The observed ignition process – manifesting as single, two, or three-stage ignition – is observed to vary with initial conditions. Analysis of ignition delay times unveils the Negative Temperature Coefficient (NTC) behavior, crucial for the existence of stable cool flames. The critical transition temperatures, such as the lower and upper turnover and the crossover temperature are also identified, along with the key chemical species produced during the two-stage ignition process. The peak temperature range for stoichiometric n-heptane CDFs is determined to be between 653 and 804 K, aligning favorably with previous experimental measurements. While the first-stage ignition delay time remains nearly constant, the second-stage ignition delay time noticeably decreases as the mixture becomes richer, up to an equivalence ratio of 32. This reduction is attributed to the rapid temperature increase caused by a larger fuel quantity, which accelerates high-temperature chemical reactions. The NTC temperature range is also seen to shorten as the mixture composition gets richer. While the six chemical kinetic models examined concur about the existence of an NTC regime, variations are observed in the threshold temperatures. The insights gained from this study enhance the understanding of CDFs, setting a foundation for future research into different fuels and varying conditions.Item DETECTION OF SIGNATURES FROM INTERNAL CONTAMINANT SOURCES USING INTELLIGENT ALGORITHMS(2023) Anthrathodiyil, Saleel; Milke, James A; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Electrical odors and smoke incidents in aviation have become a pressing concern, with over half of the detector activations resulting in false alarms, leading to uncertainties for flight crews. The escalating costs of diversions and growing awareness of associated health risks underscore the need for more reliable detection and discrimination from false alarms. This study harnesses advanced multi-sensor array technologies, intelligent algorithms, and Metal Oxide Sensors (MOS) sensors equipped with AI capabilities to detect and analyze signatures from candidate internal contaminant sources located in the cockpit. Printed circuit boards from avionics, aviation cables of different insulation, and external contaminant sources were put to failure testing to analyze the early fire signatures. These signatures were subsequently assessed using clustering algorithms and multivariate analysis to pinpoint distinct markers. Comprehensive gas analysis and light obscuration measurements further characterized the environment. Experiments were executed at both the University of Maryland and the Federal Aviation Administration (FAA) tech center, replicating diverse conditions, including an altitude simulation of 8000 ft. The focus was on the capability to distinguish between samples during the smoldering phase, leveraging a multivariate approach and gas analysis. The study also incorporated Aspirating Smoke Detection (ASD) to characterize the responses during large-scale testing. The findings pave the way for identifying and integrating innovative technologies, achieving accurate detection of early-stage signatures from internal contaminants during potential aircraft smoke events.Item Viability of Various Sources to Ignite A2L Refrigerants(MDPI, 2020-12-28) Kim, Dennis K.; Sunderland, Peter B.Environmental considerations are motivating the adoption of low global warming potential refrigerants. Most of these are mildly flammable, i.e., A2L. Their susceptibility to ignition from various ignition sources is poorly understood, particularly for the stoichiometric and quiescent mixtures that are emphasized here. The viability of fifteen residential ignition sources to ignite four A2L refrigerants is considered. Tests are performed in a windowed chamber with a volume of 26 L. The refrigerants are R-32 (difluoromethane); R-452B (67% R-32, 26% R-1234yf, and 7% pentafluoroethane); R-1234yf (2,3,3,3-tetrafluoropropene); and R-1234ze (1,3,3,3-tetrafluoropropene). Two types of ignition sources are confirmed here to be viable: a resistively heated wire at 740 °C and open flames. When the refrigerant concentration was increased slowly, candle flames and butane flames extinguished before initiating any large deflagrations. Eleven other sources were not viable: a smoldering cigarette, a butane lighter, friction sparks, a plug and receptacle, a light switch, a hand mixer, a cordless drill, a bread toaster, a hair dryer, a hot plate, and a space heater. The difficulty to ignite these refrigerants in air is attributed to their long quenching distances (up to 25 mm). Under some conditions the refrigerants were observed to act as flame suppressants.Item Polyisocyanurate Foam Pyrolysis and Flame Spread Modeling(MDPI, 2021-04-13) Chaudhari, Dushyant M.; Stoliarov, Stanislav I.; Beach, Mark W.; Suryadevara, Kali A.Polyisocyanurate (PIR) foam is a robust thermal insulation material utilized widely in the modern construction. In this work, the flammability of one representative example of this material was studied systematically using experiments and modeling. The thermal decomposition of this material was analyzed through thermogravimetric analysis, differential scanning calorimetry, and microscale combustion calorimetry. The thermal transport properties of the pyrolyzing foam were evaluated using Controlled Atmosphere Pyrolysis Apparatus II experiments. Cone calorimetry tests were also carried out on the foam samples to quantify the contribution of the blowing agent (contained within the foam) to its flammability, which was found to be significant. A complete pyrolysis property set was developed and was shown to accurately predict the results of all aforementioned measurements. The foam was also subjected to full-scale flame spread tests, similar to the Single Burning Item test. A previously developed modeling approach based on a coupling between detailed pyrolysis simulations and a spatially-resolved relationship between the total heat release rate and heat feedback from the flame, derived from the experiments on a different material in the same experimental setup, was found to successfully predict the evolution of the heat release rate measured in the full-scale tests on the PIR foam.Item USE OF MILLIGRAM-SCALE FLAME CALORIMETRY FOR CHARACTERIZING FLAMMABILITY OF FABRIC SAMPLES WITH FLAME RETARDANT TREATMENTS(2023) Roche, Thomas William; Raffan-Montoya, Fernando; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The fire hazard associated with fabrics threatens everyone’s safety, and the current standards used to reduce those hazards are expensive and time-consuming. Fabrics are a key component in clothing, upholstery, and carpentry and are present in nearly every built environment. The inherent flammability of fabrics leads to the application of flame-retardant treatments on nearly all commercial fabric products. Recently, environmental, economic and performance concerns have driven research to develop new flame retardants across a variety of materials. The military industry in particular has focused recent research efforts on flame retardant treatments for fabrics, given the challenging environments that military uniforms must endure. Current methods for testing performance of novel flame retardants, such as the Cone Calorimeter and Microscale Combustion Calorimeter can be prohibitively expensive or only provide a limited understanding of flame-retardant action. Fabrics present additional testing challenges due to their low density and thickness, effectively reducing the amount of fuel available for testing. A novel apparatus, the Milligram-scale Flame Calorimeter (MFC), has been used to test flame retardants in polymeric materials, successfully capturing gas-phase activity and with favorable comparison to Cone Calorimeter results. This study aims to expand the use of the MFC to the testing of fabrics and flame-retardant treated fabrics. Optimization tests were run to find the optimal number of fabric layers and best method for preparing samples for use in MFC. Subsequently, cotton fabrics (untreated and treated with phosphoric acid), as well as Nylon fabrics (untreated and treated with tannic acid) were characterized with MFC, and results were compared to those from the Microscale Combustion Calorimeter and Cone Calorimeter. The MFC showed similar trends in the onset of ignition, peak heat release rate, average heat release rate, char yield, and heat of combustion for the untreated fabrics with the Cone Calorimeter and Microscale Combustion Calorimeter results. The results for the flame-retarded fabrics are inconclusive and require additional testing, though the observations of the condensed-phase and gas-phase activity for the MFC samples does provide important insights on how the mechanism for the flame retardants operate.Item DEVELOPING A VELOCITY-DENSITY CURVE FOR HIGH-DENSITY CROWD SIMULATION BY ANALYZING FOOTAGE VIDEOS(2023) Zhang, Zilin; Milke, James A.; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Crowds with densities higher than 2 persons/m2 can be defined as high-density crowds. High-density crowds presenting in daily life like concerts and sports events can lead to serious people and property loss. This research work focuses on developing a new speed-density relationship for high-density crowds. The applicability of the new speed-density relationship is tested in Pathfinder, an agent-based evacuation simulation software developed by Thunderhead Engineering, to determine the impact of updating such data on the model's performance. This research also discusses several parameters and functions in Pathfinder including acceleration time and reduction factor to help model high-density crowds.Previous work is available for analyzing crowds with densities lower than 3 persons/m2. However, densities as high as 9 persons/m2 are common in many high-density crowd scenarios. The disparity between previous work and real-world situations presents a challenge for engineers to understand the crowd dynamics of high-density crowds. Developing evacuation models to predict the behavior of high-density crowds is crucial to improving the predictive ability of crowd simulation. By doing so, it helps to reduce the number of casualties in future emergencies. Real-world footage videos are analyzed in this research. With the open-source experimental footage videos provided by Jülich, a national research institution, a new speed-density curve is summarized by collecting and analyzing data from the videos. The assessment of the applicability of the new speed-density in Pathfinder focuses on four aspects: evacuation time, flow density, flow velocity, and occupants’ arrangement. Per case examined, by applying the new speed-density curve, the predicted evacuation time from Pathfinder simulation is improved from 12.6% to within 4.9% of the experimental video time. The predicted flow density is improved from 6.2% to within 0.7% of the average video density. The predicted flow velocity is improved from 25.9% to within 3.3% of the average video velocity. At the same time, it is observed that occupants in the model behave more realistically.