Masters Thesis Defense Announcement
Master of Science in Fire Protection and Administration
Name: Wenxu Yang
Date: Thursday, July 28, 2016 at 10:00 am
Location: Smith 322
Thesis Committee Chair: Dr. Aixi Zhou
Title: Pyrolysis and Combustion Properties of Selected Structural Fuels in Residential Buildings
Firebrands are a major ignition source in large scale wildland and Wildland-Urban Interface (WUI) fires. Limited studies have been reported regarding firebrand generation. It was hypothesized that firebrand production characteristics can be described by using thermal and combustion properties and geometry factors of the fuel, and the ember production characteristics will be functions of these controlling factors.
As a first step to test this hypothesis, this thesis measured the basic pyrolysis and combustion properties (at small scale) of selected structural fuels (construction materials) under a range of heating rates, radiant heat flux (HF) levels, and moisture content (MC) levels. The following seven commercially available structural fuels were selected for the study: one Southern Yellow Pine (SYP) framing lumber product, one Spruce-Pine-Fir (SPF) framing lumber product, three Oriented Strand Board (OSB) products [two sheathing types (OSB-PF and OSB-H) and one siding type (OSB-siding)], one Plywood sheathing product (CDX grade), and one Hardboard (HB) siding product.
The pyrolysis properties of the selected structural fuels were measured by using the Thermogravimetric Analysis (TGA) technique at various heating rates and different fuel MC levels. The combustion properties of the selected structural fuels were measured by using the Cone Calorimeter at various HF levels and different fuel MC levels.
The results showed strong effects of MC level on the material properties of the fuels. As the MC level increased, the density of SYP, OSB-Siding, OSB-H and CDX increased slightly, while SPF and OBS-sheathing decreased slightly. HB had the highest density at MC level 10%. The thermal conductivity of the selected fuels increased as the MC level increased. The pyrolysis properties were affected by both the MC levels and heating rate levels. The pre-exponential factor and activation energy values varied in the early stage of pyrolysis, but appeared to be more stable when the conversion factor α was 0.25 or higher. Both MC level and heating rate had strong effect on the pre-exponential factor but less effect on activation energy. The MC levels and HF levels had strong effect on the combustion properties of the selected structural fuels. Heat flux had significant effect on Time to Ignition (TTI), the higher the heat flux levels, the smaller the TTI values. MC levels had significant effect at low heat flux levels. As the MC level increased, the Critical Heat Flux (CHF) for ignition values increased for SYP and OSB-Siding, but decreased for CDX and HB. SPF, OSB-PF and OSB-H had highest CHF values at 10% MC level. The Peak Heat Release Rate (PHRR) of all selected structural materials increased as the heat flux level increased, and decreased as the MC level increased, although with a few exceptions. As the MC level increased, the Effective Heat of Combustion (EHC) of materials also increased. HF levels had less effect on the EHC values. The Mass Loss (ML) and Mass Los Rate (MRL) of materials increased as the HF level increased. MC levels showed less effect on ML and MLR. The Time to Flameout (TTF) of all materials increased as the MC level increased, but decreased as the heat flux increased.