Measurement of the Average Molecular Weights of Gaseous Pyrolyzates Produced by Combustible Solids

Published

June 30, 2025

Author(s)

Alec Tripi, Ryan Greene, Isaac Leventon, Kevin McGrattan

Abstract

Predictions of fire phenomena such as flame structure, stability, and growth made by computational fire models can be improved by incorporating an accurate description of the gaseous volatiles released by combustible solids during pyrolysis. The difficulty in this characterization is that the majority of materials release a complex mixture of gaseous species. Rather than identifying and quantifying each species, modelers often represent the average of the mixture with an effective fuel molecule. In this work, an experimental method was developed to identify the molecular formula of this representation. An organic elemental analyzer was used to determine average composition, while a heated, non-stirred pressure vessel was used to determine molecular weight. The average molecular formula was produced by the combination of these experimental results. The experimental apparatus were calibrated separately, and a series of validation tests using known composition (BBOT, sulphanilamide, urea) and molecular weight (water, naphthalene) species were performed. Validation tests found accurate elemental compositions within an average of 0.71\%, while the molecular weights of known volatiles were found within an average of 4.68\%. Poly(methyl methacrylate) and polyoxymethylene, which are known to pyrolyze primarily to their monomers, were carried through the entire experimental procedure. The molecular formulas of each pyrolyzate were found to match their monomer within 0.42\% and 30.0\% respectively. The average molecular formula of the pyrolyzates produced by Western Red Cedar, accounting for char production, was also determined. When input into fire modeling software, this formula allowed for significant improvements in ignition and flame spread behavior in comparison to a propane surrogate.

Proceedings Title

16th International Conference and Exhibition on fire science and engineering

Conference Dates

June 30-July 2, 2025

Conference Location

London, GB

Pub Type

Conferences

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Keywords

Fire Modeling, Materials Flammability, Pyrolysis

Citation

Tripi, A. , Greene, R. , Leventon, I. and McGrattan, K. (2025), Measurement of the Average Molecular Weights of Gaseous Pyrolyzates Produced by Combustible Solids, 16th International Conference and Exhibition on fire science and engineering, London, GB, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=960069 (Accessed November 23, 2025)