A Proposed Experimental Methodology for Assessing the Effects of Biophysical Properties and Energy Content on Live Fuel Flammability

• Author / Creator

  Melnik, Oleg

• The effectiveness of fire management tactics and safety of firefighters strongly depend on the reliability of fire behaviour predictions that is currently limited by a lack of understanding of the flammability of live fuel. Until now fire modeling has been primarily based on the flammability of dead fuel using the assumption that combustion of the live fuel has a very limited effect on fire behaviour. However, the analysis of the existing data revealed that live fuel constituted from 48% to 60% of fuel consumed during the passage of a flame-front, meaning that live fuel plays a significant role in determining frontal fire intensity and fire behaviour. Introducing a new definition of flammability and a test method for flammability assessment, this study identifies how and to what extent live fuel and its properties may affect frontal flame intensity. By evaluating flammability directly in a flame, the proposed oxygen consumption calorimetry method better represents the high-intensity combined radiative and convective heat transfer prior to ignition as well as the conditions of oxygen deficiency and high concentrations of water vapor within the flame-front. The flammability of live fuel consumed within the flame-front was defined as energy release contribution to the frontal flame and represented the energy-generation component of the energy balance of the flame-front rather than just an energy content of separate fuel elements. The flammability was measured as the change in energy release from the flame resulting from interaction with live fuel during average flame-front residence time. Assessing the flammability of fresh shoots rather than just foliage allowed for better representation of the live plant material consumed in the flame-front. Live fuel flammability range, factors, and seasonal trend were investigated on a tree branch scale and a new high-resolution volume measuring technique was also introduced. The variation in live fuel flammability for white spruce was more than twice that measured using existing techniques suggesting that the actual changes in live fuel flammability have been underestimated by current fire modelling systems. Measured negative values of flammability for new shoots in the beginning of the season indicated a reduction in the energy release of the combined system of live fuel and frontal flame assumed to result from the high water content of live fuel and oxygen deficiency. Dry matter content and variables characterizing chemical composition of the fuel were replaced by a newly-introduced variable – energy content per unit of fresh mass or volume. Using the gravimetric approach, the energy content did not improve the prediction of flammability; however, when using the volumetric approach, variation in flammability was better explained by energy content than by water content. The proposed volumetric multivariable flammability model (adjusted R^2 = 0.87) was able to better predict flammability compared with the volumetric single-variable models (adjusted R^2 = 0.79). The Canadian Fire Behaviour Prediction System assumes only one seasonal maximum in flammability occurring in early-mid June, but it was instead observed one month earlier. Two additional spikes in flammability occurred in early July and mid-August, when the lowest seasonal values were expected. The mid-August spike in the flammability was caused by a second seasonal minimum in water content induced by drought. If applied to a known amount of live and dead fuel in a vegetative canopy, the proposed approach allows for evaluation of the combined energy release contribution to the flame-front by live and dead fuel on a vegetative canopy scale without modeling fuel consumption. This measure of the forest stand energy release response to fire conditions can further be used in the development of a numerical stand characteristics-based fuel classification and as a forest stand flammability input to fire behaviour modelling systems.

• Subjects / Keywords

  • Oxygen consumption calorimtry
  • Live fuel flammability
  • Energy content

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3862BH01

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.