The Effect of Orientation on the Ignition of Solids
The ignition of a solid is an inherently complex phenomenon influenced by heat and mass transport mechanisms that are, even to this day, not understood in entirety. In order to use ignition data in meaningful engineering application, significant simplifications have been made to the theory of ignition. The most common way to classify ignition is the use of material specific parameters such as such as ignition temperature (Tig) and the critical heat flux for ignition (CHF). These parameters are determined through standardized testing of solid materials – however, the results of these tests are generally used in applications different from the environments in which these parameters were actually determined. Generally, ignition temperature and critical heat flux are used as material properties and are presented readily in sources such as the SFPE Handbook. However, these parameters are not truly material properties; each are inherently affected by the environment and orientation in which they are tests. Ignition parameters are therefore system dependent, tied to the conditions in which the parameters are determined.
Previous work has demonstrated that ignition parameters (such as Tig or CHF) for the same material can vary depending on whether the sample is tested in a vertical or horizontal orientation. While the results are clear, the implications this may have on the use of ignition data remains uncertain. This work outlines the fundamental theory of ignition as well as a review of studies related to orientation.
The aim of this study it to analyze the influence of sample orientation on ignition parameters. All experimental work in this study was conducted using cast black polymethyl methacrylate (PMMA or commonly referred to as acrylic). This study explores ignition parameters for PMMA in various orientations and develops a methodology through which orientation can be incorporated into existing ignition theory. An additional study was also conducted to explore the statistical significance of current flammability test methodologies. Ultimately, this study outlines the problem of the system dependency of ignition and provides commentary on the use of ignition data in engineering applications