In this study, a burning model is used to link the molecular-level processes of flaming combustion measured in thermal analysis to the fire response of a polymer at the continuum level. A flammability parameter that includes ignitability and burning rate, driven by heat release, emerging from this analysis is called the Fire Growth Capacity (FGC). The FGC was measured in a micro (10-6 kg) scale combustion calorimeter for 30 polymers, and successfully ranked the expected fire performance of these polymers in bench (kg) scale flame and fire tests
The prevalence of lithium batteries on aircraft is a potential safety hazard because of the risk of thermal runaway—a rapid rise in temperature and pressure, and the release of flammable gases. The goal of this study was to create a framework for potential guidelines for a standardized test method for the classification of a lithium battery’s cell hazard due to thermal runaway. Classifying a cell’s hazards due to thermal runaway can help determine appropriate mitigation methods for their use and transport.
Some of the cells were overcharged and other cells were overheated at various heating rates to force thermal runaway. The maximum cell case temperature, cell case temperature at the onset of thermal runaway, and peak percent pressure rise were measured. The thermal runaway vent gases were collected and analyzed for hydrogen, carbon monoxide, carbon dioxide, and hydrocarbon concentrations. The gas and pressure measurements were used to calculate the lower flammability limit (LFL) of the vent gas. The average maximum air-filled volumes that become flammable per cell after thermal runaway were determined and evaluated.
Lithium manganese dioxide (LiMnO2) cylindrical primary cells at 100% state of charge (SOC) of type CR123a 3V 1500mAh were tested. There were differences between the overheat method and the overcharge method. The methods varied by test duration, repeatability, and test results. The overheat method was the quickest and most repeatable method for producing a thermal runaway event. Lithium cobalt oxide (LiCoO₂) cylindrical secondary cells at 30% SOC, of type 18650 3.7V 2600mAh were tested at various heating rates. The results suggest that the heating rate significantly affects an 18650-sized cell’s thermal runaway. Cells heated with a heating rate of less than 12°C/min produced a lesser quantity of vent gas and measured a lower maximum cell case temperature than cells heated with a heating rate of more than 17°C/min. A heating rate between 12°C/min and 17°C/min produced mixed results. LiCoO₂ pouch cells at 30% SOC 3.7V 2500mAh, were also tested at various heating rates. The results suggest that the heating rate moderately affects a pouch cell’s thermal runaway. For every 10 C°/min increase in heating rate, the total vent-gas volume increased by 0.057 L, the percent pressure rise increased by 0.89%, and the concentration of carbon dioxide decreased by 2.3%.
Prompt fire detection in cargo compartments on board transport aircraft is an important safety feature. Concern has been expressed for the activation time of contemporary detection technologies installed on aircraft. This project will deliver a continuation of research on the issues that have been identified relative to fire detection improvements in cargo compartments on aircraft, with a particular emphasis on freighters. Gas sensors and dual wavelength detectors were demonstrated in a previous phase to be responsive to fires in the previous experiment program. Detectors placed inside a Unit Loading Device (ULD) responded quickly to the array of fire sources. Thus, a further exploration of these observations is conducted including wireless technology along with an analysis of the effects of leakage rates on fire signatures inside ULDs. One primary goal is to assess the differences in fire detection time for detectors located within ULD versus those located on the ceiling of the cargo compartment for fires which originate in a ULD. The results indicated the detector location with the shortest activation time is inside of the ULD. Within the ULD, the wireless detector outperformed both air sampling detectors, however, the results could vary if threshold levels were more restrictive.