Journal Article Reports on Engineering Model for the Pyrolysis of Materials

A new peer-reviewed journal article on developing an engineering model for the pyrolysis of materials has been published in the Fire Safety Journal. The manuscript was authored by Jonathan Hodges, Service Line Leader in Advanced Modeling at Jensen Hughes, and Jason Floyd, research engineer at the Fire Safety Research Institute (FSRI), part of UL Research Institutes in collaboration with researchers at Virginia Tech, and the National Institute of Technology (NIST).

Accurately representing the time dependent heat release rate of fuels is critical to performance-based design in fire safety applications. Existing simplified models either use average pyrolysis rates at different heat fluxes or do not account for the change in burning behavior at higher heat transfer rates. This research aimed to develop a simple approach for modeling fire growth that relies on simple testing rather than development of detailed kinetic schemes. 

The paper presents the theoretical basis of a scaling-based pyrolysis model, S-Pyro. The model is based on the concept of maintaining the shape of a reference heat release rate per unit area curve but scaling the magnitude and time based on a dynamic thermal exposure. The model has been implemented in the computational fluid dynamics software Fire Dynamics Simulator (FDS). The model is validated with solid-phase only and multi-phase simulations of cone calorimeter experiments. The solid-phase simulations evaluated the capability of the model to predict the heat release rate per unit area of 149 materials tested at heat fluxes other than the reference flux. Multi-phase simulations of bench-scale fire experiments with a single material, Canada Pine and Spruce plywood, were used to evaluate the performance of the pyrolysis model in FDS. The model uncertainty was lower for high heat release rate materials, with the model uncertainty approaching the experimental uncertainty at higher burning rates.

The primary objectives of this research were to:

• Develop a scaling-based model to dynamically scale cone calorimeter data.
• Validate the model using experimental measurements from 149 different materials.
• Implement pyrolysis model as an option in Fire Dynamics Simulator (FDS).
• Evaluate the impact of the model on burning behavior in FDS simulations.

Conclusions

In virtual cone tests for 149 materials (including cellulosic materials, polymers, other materials, and material mixtures), this method predicted peak and 60-second average heat release rate within 20 %. Time to peak had a 50 % error. The approach shows great promise as a simple engineering approach to predicting fire growth, however, further work is required to test the method at full scale. Additionally, there are limitations in the method that must be explored such as how to handle modeling fire growth when the material thickness varies from that tested in a cone calorimeter.

“Predicting fire growth from first principles is fraught with challenge,” said Jason. “Having a method that makes reasonable predictions with limited grid sensitivity that only needs easy to obtain or often published (include at materials.fsri.org) cone calorimeter data, would be of great help to practitioners in design and forensics and to researchers using real world fuels in testing.”

This project was funded by NIST and the Federal Railroad Administration.

About Fire Safety Journal

Fire Safety Journal is the leading publication dealing with all aspects of fire safety engineering. Its scope is purposefully wide, as it is deemed important to encourage papers from all sources within this multidisciplinary subject, thus providing a forum for its further development as a distinct engineering discipline. This is an essential step towards gaining a status equal to that enjoyed by the other engineering disciplines.