Combustibility of a mixture of live and dead fuel components

The problem of predicting the rate of spread of a linear fire front in a fuel bed composed of one live and one dead fuel component in no-slope and no-wind conditions is addressed. Two linear models based on the mass fraction of each fuel component are proposed to predict the rate of spread of a fire front as a function of the mass fraction of the dead or dry fuel component. Experimental results obtained with two different mixtures show that for each fuel mixture there is a threshold value of mass concentration of the dead fuel below which the fire front does not spread. The rate of spread results compare favourably with the proposed models. A composite fuel moisture content of the fuel bed is shown to be a good descriptor of the rate of spread of the mixture. An exponential model using composite fuel moisture content of the fuel bed is proposed to estimate the rate of spread of the mixture and a comparison is made with the concept of fuel curing that is used to characterise live fuels.

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Convective heat transfer in fire spread through fine fuel beds

International Journal of Wildland Fire ◽

10.1071/wf09021 ◽

2010 ◽

Vol 19 (3) ◽

pp. 284 ◽

Cited By ~ 39

Author(s):

W. R. Anderson ◽

E. A. Catchpole ◽

B. W. Butler

Keyword(s):

Heat Transfer ◽

Wind Speed ◽

Moisture Content ◽

Flame Front ◽

Free Stream ◽

Surface Wind ◽

Surface Wind Speed ◽

Fuel Moisture ◽

Fire Front ◽

Fuel Moisture Content

An extensive set of wind-tunnel fires was burned to investigate convective heat transfer ahead of a steadily progressing fire front moving across a porous fuel bed. The effects of fuel and environmental variables on the gas temperature profile and the ‘surface wind speed’ (gas velocity at the fuel bed surface) are reported. In non-zero winds, the temperature of the air near the fuel bed surface decays exponentially with distance from the fire front. In zero winds, the temperature decreases rapidly within a very short distance of the flame front, then decays slowly thereafter. The maximum air temperature decreases as the free stream wind speed, packing ratio and fuel moisture content increase. The characteristic distance of the exponential decay increases strongly with the free stream wind speed and decreases with the packing ratio and surface area-to-volume ratio of the fuel. The surface wind speed depends strongly on the free stream wind speed, and to a lesser extent on packing ratio, fuel bed depth and fuel moisture content. There are three general regimes for the surface flow: (1) a constant velocity flow of approximately half the free stream flow, far from the flame front; (2) an intermediate zone of minimum flow characterised by low or reversed flow; and (3) a region near the flame front where the velocity rises rapidly almost to the free stream velocity. The boundaries between the three regions move further from the flame front with increasing wind speed, in a way which is only slightly affected by fuel geometry.

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Empirical modelling of surface fire behaviour in maritime pine stands

International Journal of Wildland Fire ◽

10.1071/wf08023 ◽

2009 ◽

Vol 18 (6) ◽

pp. 698 ◽

Cited By ~ 51

Author(s):

Paulo M. Fernandes ◽

Hermínio S. Botelho ◽

Francisco C. Rego ◽

Carlos Loureiro

Keyword(s):

Wind Speed ◽

Moisture Content ◽

Fire Spread ◽

Fire Intensity ◽

Fuel Moisture ◽

Fire Behaviour ◽

Spread Rate ◽

Surface Fire ◽

Rate Of Spread ◽

Fuel Moisture Content

An experimental burning program took place in maritime pine (Pinus pinaster Ait.) stands in Portugal to increase the understanding of surface fire behaviour under mild weather. The spread rate and flame geometry of the forward and backward sections of a line-ignited fire front were measured in 94 plots 10–15 m wide. Measured head fire rate of spread, flame length and Byram’s fire intensity varied respectively in the intervals of 0.3–13.9 m min–1, 0.1–4.2 m and 30–3527 kW m–1. Fire behaviour was modelled through an empirical approach. Rate of forward fire spread was described as a function of surface wind speed, terrain slope, moisture content of fine dead surface fuel, and fuel height, while back fire spread rate was correlated with fuel moisture content and cover of understorey vegetation. Flame dimensions were related to Byram’s fire intensity but relationships with rate of spread and fine dead surface fuel load and moisture are preferred, particularly for the head fire. The equations are expected to be more reliable when wind speed and slope are less than 8 km h–1 and 15°, and when fuel moisture content is higher than 12%. The results offer a quantitative basis for prescribed fire management.

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Flame characteristics, temperature - time curves, and rate of spread in fires propagating in a bed of Pinus pinaster needles

International Journal of Wildland Fire ◽

10.1071/wf02063 ◽

2003 ◽

Vol 12 (1) ◽

pp. 67 ◽

Cited By ~ 64

Author(s):

José M. C. Mendes-Lopes ◽

João M. P. Ventura ◽

José M. P. Amaral

Keyword(s):

Wind Speed ◽

Moisture Content ◽

Pinus Pinaster ◽

Flame Height ◽

Fuel Moisture ◽

Propagation Models ◽

Fire Propagation ◽

Rate Of Spread ◽

Fuel Moisture Content ◽

Flame Angle

An extensive set of experiments was carried out in order to collect data to validate fire propagation models being developed in the context of an European research project. The experiments were performed in a dedicated burning tray (2.0 m × 0.70 m working section), where wind velocity, fuel moisture content and slope were varied to study fire propagation in beds of Pinus pinaster needles. All the runs were videotaped and, from the recordings, information on flame geometry (i.e. flame height, flame length and flame angle) and rate of spread was obtained. Temperature measurements were also carried out by a small tower of six thermocouples at different heights above the fuel bed. Results show that headfire rate of spread increases steeply with wind speed for wind-driven fires but does not depend on wind speed for backing fire spread rates. Rate of spread increases slightly with slope for up-hill propagation, and is not slope dependent for down-hill cases. Rate of spread decreases when fuel moisture content increases. Flame angle and flame height are also dependent on wind velocity, slope, and fuel moisture content. The importance of temperature for fire propagation is discussed, emphasizing the role of radiation heat transfer in the process. Correlations between temperature and other indicators of fire behaviour (namely the rate of spread) are presented. Results are discussed and compared. The results obtained provide a good database for the assessment of fire propagation models.

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Effects of curing on grassfires: I. Fuel dynamics in a senescing grassland

International Journal of Wildland Fire ◽

10.1071/wf14145 ◽

2015 ◽

Vol 24 (6) ◽

pp. 828 ◽

Cited By ~ 11

Author(s):

Susan Kidnie ◽

Miguel G. Cruz ◽

Jim Gould ◽

David Nichols ◽

Wendy Anderson ◽

...

Keyword(s):

Moisture Content ◽

Fuel Moisture ◽

Fire Dynamics ◽

Sampling Protocol ◽

Fuel Component ◽

Dead State ◽

Fuel Dynamics ◽

Green Fuels ◽

Soil Dryness ◽

Fuel Moisture Content

Grass senescence, or grassland curing, is a dynamic process in which grass fuels transition from a live to dead state and, in turn, influence fire dynamics. In the present study we examined the process of curing with specific consideration of changes in fuel structure that will affect potential fire behaviour. Our sampling protocol expanded the fuel component groups from two (live and dead) to four (green, senescing, new dead and old dead fuel). We found that all these components had significant fuel moisture content differences, thereby justifying our sampling protocol. Visual curing assessment predominantly resulted in an over-prediction bias of curing level and failed to capture the effect of the senescing process on fuel availability to combust due to misclassification of fuel components (e.g. senescing fuels with high fuel moisture content were classified as dead fuels because of their colouration). Models were developed to estimate the: (1) proportion of senescing and green fuels from knowledge of the current year’s dead fuel proportion; and (2) actual curing level from fuel moisture content and soil dryness level.

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A generic, empirical-based model for predicting rate of fire spread in shrublands

International Journal of Wildland Fire ◽

10.1071/wf14130 ◽

2015 ◽

Vol 24 (4) ◽

pp. 443 ◽

Cited By ~ 64

Author(s):

Wendy R. Anderson ◽

Miguel G. Cruz ◽

Paulo M. Fernandes ◽

Lachlan McCaw ◽

Jose Antonio Vega ◽

...

Keyword(s):

Moisture Content ◽

Experimental Studies ◽

Fire Spread ◽

Fuel Moisture ◽

Fire Behaviour ◽

Weather Factors ◽

Vegetation Height ◽

Rate Of Spread ◽

Wide Range ◽

Fuel Moisture Content

A shrubland fire behaviour dataset was assembled using data from experimental studies in Australia, New Zealand, Europe and South Africa. The dataset covers a wide range of heathlands and shrubland species associations and vegetation structures. Three models for rate of spread are developed using 2-m wind speed, a wind reduction factor, elevated dead fuel moisture content and either vegetation height (with or without live fuel moisture content) or bulk density. The models are tested against independent data from prescribed fires and wildfires and found to predict fire spread rate within acceptable limits (mean absolute errors varying between 3.5 and 9.1 m min–1). A simple model to predict dead fuel moisture content is evaluated, and an ignition line length correction is proposed. Although the model can be expected to provide robust predictions of rate of spread in a broad range of shrublands, the effects of slope steepness and variation in fuel quantity and composition are yet to be quantified. The model does not predict threshold conditions for continuous fire spread, and future work should focus on identifying fuel and weather factors that control transitions in fire behaviour.

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A laboratory-based quantification of the effect of live fuel moisture content on fire spread rate

International Journal of Wildland Fire ◽

10.1071/wf15114 ◽

2016 ◽

Vol 25 (5) ◽

pp. 569 ◽

Cited By ~ 21

Author(s):

Carlos G. Rossa ◽

Ricardo Veloso ◽

Paulo M. Fernandes

Keyword(s):

Moisture Content ◽

Laboratory Experiments ◽

Fire Spread ◽

Fuel Moisture ◽

Drying Process ◽

Spread Rate ◽

Rate Of Spread ◽

Live Fuels ◽

Fuel Moisture Content ◽

Content Range

Observational evidence of an effect of live vegetation moisture content on fire spread rate remains extremely scarce despite the significance of fire activity in fuel complexes dominated by live components. This study assessed the moisture content effect of quasi-live fuels on fire spread rates measured in laboratory experiments. Fuel beds were built by vertically placing vegetation clippings to reproduce the natural upright fuel structure. The fuel drying process during storage resulted in a wide moisture content range (13–180%). An exponential damping function was fitted to rate of spread observations in four fuel types, indicating that rate of spread is halved by an increase in live moisture content from 50 to 180%. This effect, especially at higher moisture contents, was weaker than that predicted by theoretical formulations and from studies in mixtures of dead and live fuel.

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Short communication: On the effect of live fuel moisture content on fire-spread rate

Forest Systems ◽

10.5424/fs/2017263-12019 ◽

2018 ◽

Vol 26 (3) ◽

pp. eSC08 ◽

Cited By ~ 8

Author(s):

Carlos G. Rossa ◽

Paulo M. Fernandes

Keyword(s):

Moisture Content ◽

Short Communication ◽

Experimental Studies ◽

Fire Spread ◽

Fuel Moisture ◽

Rate Of Spread ◽

Mediterranean Shrubland ◽

Live Fuels ◽

Live Fuel Moisture ◽

Fuel Moisture Content

Aim of study: To reconcile the effects of live fuel moisture content (FMC) on fire rate of spread (ROS) derived from laboratory and field fires.Methods: The analysis builds on evidence from previous fire-spread experimental studies and on a comparison between two functions for the FMC damping effect: one derived from field burns, based on dead FMC, and another derived from laboratory trials, based on a weighted FMC (dead and live fuels).Main results: In a typical Mediterranean shrubland, laboratory and field-derived FMC damping functions are linearly related, which is explained by the correlation between monthly average live and dead FMC variation throughout the year. This clarifies why the effect of live FMC on real-world fires ROS has remained elusive.Research highlights: By providing evidence that the most significant effect of FMC on ROS is independent of vegetation phenology (dead or live condition), and explaining why in specific situations dead FMC is sufficient to provide satisfactory ROS predictions, our results can assist future modelling efforts.

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