Characterizing a Firefighter’s Immediate Thermal Environment in Live-Fire Training Scenarios

Detailed characterization of a firefighter’s typical thermal exposures during live-fire training and responses can provide important insights into the risks faced and the necessary protections, protocols, and standards required. In order to gather data on representative thermal conditions from a firefighter’s continually varying local environment in a live-fire training exercise, a portable heat flux and gas temperature measurement system was created, calibrated, and integrated into firefighter personal protective equipment (PPE). Data were collected from 25 live-fire training exposures during seven different types of scenarios. Based on the collected data, mild training environments generally exposed firefighters to temperatures around 50 degrees Celsius and heat fluxes around 1 kW/m2, while severe training conditions generally resulted in temperatures between 150 degrees Celsius and 200 degrees Celsius with heat fluxes between 3 kW/m2 and 6 kW/m2. For every scenario investigated, the heat flux data portrayed a more severe environment than the temperature data when interpreted using established thermal classes developed by the National Institute for Standards and Technology for electronic equipment used by first responders. Local temperatures from the portable measurement system were compared with temperatures measured by stationary thermocouples installed in the training structure for 14 different exposures. It was determined the stationary temperatures represented only a rough approximate bound of the actual temperature of the immediate training environment due to the typically coarse distribution of these sensors throughout the structure and their relative (fixed) distance from the fire sets. The portable thermal measurement system has provided new insights into the integration of electronic sensors with firefighter PPE and the conditions experienced by firefighters in live-fire training scenarios, which has promise to improve the safety and health of the fire service.Ope

Characterizing a Firefighter's Immediate Thermal Environment in Live-Fire Training

In 2013, over 7,500 firefighters were injured during training related activities, including highrisk, but necessary, live-fire training. Although a standard for live-fire training exists, little physical data have been collected from the thermal environment encountered in this type of training. Acquiring data from live-fire training scenarios would be extremely beneficial to the fire service; it would allow for the evaluation and improvement of live-fire training evolutions as well as testing standards for firefighter personal protective equipment (PPE). In order to gather data from a firefighters immediate thermal environment in a live-fire training exercise, a portable heat flux and gas temperature measurement system was created and integrated into firefighter PPE. The system was tested and calibrated in a laboratory setting at the National Institute of Standards and Technology and then used to measure the ambient temperature and incident heat flux of a firefighters immediate environment in live-fire scenarios. Data were collected from 28 live-fire training evolutions conducted during seven different training scenarios. It was discovered that a mild thermal environment generally contained temperatures between 50C and 75C and heat fluxes around 1 kW/m2, while a severe thermal environment generally contained temperatures between 150C and 225C and heat fluxes between 3 kW/m2 and 6 kW/m2. Additionally, heat flux proved to be a more effective metric than temperature in evaluating the severity of the thermal environment. The portable thermal measurement system has provided new insights into conditions experienced by firefighters, which will greatly improve the safety and health of the US fire service.Ope

Repeatability of pre-flashover fire patterns on gypsum wallboard.

Unwanted fires result in loss of life and property. These fires can also create an adverse economic impact on a community. The investigation of fires provides a means to identify the cause of the fire in order to develop a knowledge base that could enable the elimination of that cause and thus reduce the losses from unwanted fires. Questions about the lack of science in the practice of fire investigation have been raised during the review of several arson homicide cases and a forensics science review by the U.S. National Academy of Sciences. Specifically, the National Academy of Sciences indicated that “...research is needed on the natural variability of burn patterns...” This study addresses that need in two ways: 1. Examining the repeatability of several small fire sources and the fire patterns that were generated by those fires. 2. Examining the capability of numerical models to simulate the fires and the resulting fire patterns based on input data collected from engineering reference sources, bench-scale experiments, and full-scale fire experiments. This manuscript highlights the many uncertainties involved in what appear to be simple fire experiments. Uncertainties related to fuel type, measurement methods, and analysis techniques were examined. The objective of the research was to examine the repeatability of pre-flashover fire patterns generated from exposure to short duration (300 seconds maximum), well characterized fires. Three different fuels were used: natural gas, gasoline, and polyurethane foam. Each fuel had a similar top surface area. The heat release rate data showed that the variability between replicates was greater for more complex fuels. The variation in peak heat release rate with the natural gas was similar to the expanded uncertainty of the measurement system, 11%. However, the variation in the peak heat release rates of the gasoline and the polyurethane foam increased due to increased uncertainties in the burning behavior of the fuels. The variability in the heat release rate of the fires resulted in higher levels of variability of the replicate fire patterns. The maximum fire pattern heights generated from the natural gas and gasoline fires were shown to have uncertainties of 18% or less based on a Type A statistical analysis with 95% confidence limits. The comparison of the fire pattern heights and the mean flame height demonstrated that the steady state natural gas fires exhibited the highest level of agreement and polyurethane foam fueled fire exhibited the least agreement, with the gasoline fueled fires in between. A range of methods used to simulate characteristics of fires were applied using data from the source fire experiments as input. The empirical-based predictions for heat flux to a target under-predicted the measured values. The gasoline fueled fires exhibited best agreement of 22% or less for the heat flux predictions. The polyurethane foam results exhibited the worst agreement with a difference of at least 40% between the measured and calculated values. Improved understanding of the radiative fraction from different fuels would improve the capability of the predictions. The best agreement between measured flame height, the measured height of the fire pattern, and flame height predictions occurred with the gasoline fueled fires. Given the overlap of the expanded uncertainty and predicted range of values, the measured and predicted heights would be considered similar. The gasoline fueled fires released the highest amount of energy and had a higher radiative fraction than the natural gas and polyurethane foam fueled fires. The agreement between the computational fluid dynamics predicted values and the measurements from these experiments demonstrated examples of agreement that were within the measurement uncertainty estimates as well as examples with poor agreement. The differences were driven in some cases by limitations within the combustion sub-model close to the burner surface; as the distance between the burner surface increased, the predicted values tended to converge with the measured values. The wall located adjacent to the burn had a significant impact on the flow field in and around the flame and plume region. The horizontal flame movements observed during the experiments was not simulated to the same degree by the model. Given the areas around the flame have steep thermal gradients; small differences in position can result in large differences in temperature and heat flux. The models are useful tools for gaining insight into fire behavior but in many cases many require specific experimental data for input or for validation. The availability of well characterized input data is limited, and data for newer materials is unavailable. Additional research is needed for modeling data development protocols. Improved data repositories are also needed. Further research is needed to understand the appropriate resolution for implementing the results based on fuel type, fuel geometry, and ventilation. Most importantly, there is a critical need to extend this research to better understand the capabilities and limitations of predictive methods using fuels and scenarios that fire investigators are likely to encounter during a fire investigation