The Use of Quasi-Steady State Experimental Methods for the Purpose of Measuring Chemical Yields for use in Fire Hazard Assessment

There are numerous steady state and quasi steady state experimental methods that can be used to measure the production of chemical byproducts from burning materials. The yield of these products can be calculated where the mass loss rate is measured. Establishing chemical yields from burning materials, which is integral for quantifying the potential hazard of exposure, is challenging. This is, in part, because the chemical yields are not simply a result of material properties but are also impacted by the availability of oxygen in the local atmosphere of the burning material. The equivalence ratio concept, representing the fuel to oxidizer ratio over the material’s stoichiometric value, can be used as an indicator of burning conditions such that the onset of ventilation-controlled burning (equivalence ratio >1) can be found. It is well known that ventilation-controlled burning conditions result in an increased yield of chemical species that are hazardous to health. As a result of this, any experimental apparatus that is used to collect product yields from burning materials must be able to replicate equivalence ratios exceeding one. There are a limited number of studies directly comparing experimental methods where equivalence ratios and product yields are collected. Where comparison is made, the comparisons often make use of data collected independently by different research groups. This inevitably results in uncertainty regarding the variation of material properties as well as contrasting methodologies for equivalence ratio and species yield calculation.
In this work the product yields are reported for cast Poly (methyl methacrylate) (PMMA) (6 and 25 mm thick) using the fire propagation apparatus (FPA) and the open controlled atmosphere cone calorimeter (OCACC). The gas inflow rate and the imposed heat flux are used to alter local atmospheric conditions and thus control the global equivalence ratio while the oxygen concentration of inflowing gas are maintained at ambient (20.95 vol.% O2). This study discusses the differences between experimental apparatus where plotted data is taken from instantaneous data sampling. The study highlights the importance of defining a clear calculation methodology where reporting global equivalence ratio data to ensure that data collection methods are reproducible. It was concluded that the FPA and OCACC produce comparable chemical yields where instrumental operational conditions are suitably input. CO/CO2 yields indicate that both instruments are suitable “physical fire models” for toxic potency assessment but further comparison between other chemical species is required. Optimal conditions for collecting material input data using both the FPA and OCACC are established for the case of cast PMMA but further work is needed to expand the materials and chemical species discussed in this study