Application of fire calorimetry to understand factors affecting flammability of cellulosic material: Pine needles, tree leaves and chipboard
Jervis, Freddy Xavier
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Calorimetry, the science of measuring heat from chemical reactions and physical changes, is one to the most valuable tools fire safety engineering have at their disposal. Calorimetric devices such as the cone calorimeter and the fire propagation apparatus (FPA) give us the means to evaluate and understand how different materials burn at a small scale. Due to fire being affected by many different environmental factors, these devices help us to isolate and examine how each factor affects fire as a whole and be able to apply this knowledge to tools that can be used at larger scales. This thesis reports various pieces of work on different calorimetric studies done on cellulosic material used in today’s natural and built environment. All experimental tests herein are done using the FPA, the state of the art calorimeter for fire safety studies. The experimental techniques presented here show how invaluable calorimetry is in giving us key insights on the combustion dynamics of fire related processes. The thesis is presented in manuscript style. Each chapter is a stand alone research work intended for publication with the exception of the first and last chapter; intended to introduce these and their relevance to the science and the last to summarize on overall findings and recommended improvements. Chapter 2 presents a study on the burning of live and dead pine needles. Pine forests present a relatively high flammability risk comprised in great part by pine needles. Different moisture content, flow conditions and their interrelationship is studied on the different parameters affecting the combustion processes. Overall, the results show that fire physics and chemistry vary with fuel and flow conditions and that moisture content is not the only difference between live and dead fuels but that the needle bed physiochemical mechanisms matter as well. This is the first time calorimetry data is presented on the burning of live and dead pine needles. Chapter 3 complements chapter 2 with an added in-depth analysis on the effect of different pine needle species, fuel load and imposed heat insult. Interrelationship between these variables is shown to have a strong effect on the overall combustion process. Fuel load is shown to be an essential condition to know as it gives a direct indication on the intensity of the fire. Flow is shown to have a varied effect depending on the fuel load, it can either aid or be detrimental to the overall combustion process especially relating to ignition times. Chapter 4 is a study on the effect of leaf morphology to flammability of different natural fuels. This study is a direct extension of the work presented in the paper Belcher et al (2010) in Nature Geoscience. Representative natural fuel samples from the Triassic/Jurassic Boundary, a time period of great importance because it marked a time of major environmental changes, are used to evaluate fire activity as a whole during this time period. The study shows that smaller leaf area and larger surface area to volume ratio show a strong correlation to an increase in flammability of these fuels. The research presents new insight into how leaf morphology can be used as a tool to assess the effect of fire activity around the globe and how closely vegetation is linked to this. Chapter 5 presents a study on flammability of chipboard. Wood being an inhomogeneous, non-isotropic material presents researchers with a complex problem due to its burning behavior. Wood has been a preferred construction material since far back and is widely used in construction today. Different oxygen levels, heat insults, material thicknesses and densities and the interrelationship between these variables are assessed to observe the effect on the flammability of chipboard. Density and thickness is shown to have little effect on the overall burning dynamics with thermally thick samples apart from the increased fuel content. Oxygen levels and imposed heat insults, however, show a wide range of effects and the interrelationship proves to be quite important during the combustion process. The research outlines how char formation is affected by the different variables and how important this process becomes along the overall combustion process. Calorimetric studies are presented that illustrate the use of these devices to study the effect of varying environmental conditions and the importance of their interrelationships on both natural and built environment fuels. The works highlight the importance of first establishing the dynamics of the combustion process in order to be able to extract combustion parameters that are needed for modeling fires better in both wildland and built environments.