SUMMARYThis paper documents the first of the two interrelated studies that were conducted to more fundamentally understand the scalability of flame heat flux, the motivation being that it has been reported that flame heat flux back to the burning surface in bench-scale experiments is not the same as for large-scale fires. The key aspect was the use of real scale applied heat flux up to 200 kW/m 2 which is well beyond that typically considered in contemporary testing. The main conclusions are that decomposition kinetics needs to be included in the study of ignition and the energy balance for steady burning is too simplistic to represent the physics occurring.An unexpected non-linear trend is observed in the typical plotting methods currently used in fire protection engineering for ignition and mass loss flux data for several materials tested and this nonlinearity is a true material response. Using measured temperature profiles in the condensed phase shows that viewing ignition as an inert material process is inaccurate at predicting the surface temperature at higher heat fluxes. The steady burning temperature profiles appear to be invariant with applied heat flux. This possible inaccuracy was investigated by obtaining the heat of gasification via the 'typical technique' using the mass loss flux data and comparing it to the commonly considered 'fundamental' value obtained from differential scanning calorimetry measurements. This comparison suggests that the 'typical technique' energy balance is too simplified to represent the physics occurring for any range of applied heat flux. Observed bubbling and melting phenomena provide a possible direction of study.
This paper investigates the thermal conditions at the surface and at depth of 1.8 cm (3/4-inch) maple plywood exposed to heat fluxes between 6 and 15 kW/m 2 in the cone calorimeter for up to 8 hours. The minimum heat flux for unpiloted smoldering ignition was 7.5 kW/m 2 and compared favorably to classical self-heating theory. The role of selfheating was explored via temperature measurements distributed within the specimens. Elevated subsurface temperature profiles indicated self-heating was an important ignition factor resulting in ignition at depth with smolder propagation to the surface and into the material. The ignition depth was shown to be a function of the heat flux with the depth moving towards the surface as the heat flux increased. Supporting work included sensor calibration testing, mass loss rate analysis, char depth testing and computer modeling. The calibration testing showed optical pyrometer This research would not have been possible without the support of Hughes Associates, Inc., who provided financial support, testing facilities and invaluable technical resources. I would also extend thanks to WPI for providing a solid foundation in fire protection engineering, and allowing me to pursue this research opportunity and to apply it towards the requirements for graduation. Finally, none of the above would have ever happened if not for the opportunity provided by the Nassau Bay Volunteer Fire Department in my old hometown of Nassau Bay, Texas. It was during my service with the NBVFD that I discovered the field of fire protection engineering, WPI and a new career. iii TABLE OF CONTENTS ABSTRACT……………………………………………………………………………….i ACKNOWLEDGMENTS……………………………………………………………….ii LIST OF FIGURES………………………………………………………………….….vi
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