Effects of wind velocity and slope on flame properties

1996 ◽  
Vol 26 (10) ◽  
pp. 1849-1858 ◽  
Author(s):  
David R. Weise ◽  
Gregory S. Biging
Keyword(s):  
Froude Number ◽  
Wind Velocity ◽  
Fire Behavior ◽  
Flame Length ◽  
Parameter Estimates ◽  
Combined Effects ◽  
Field Scale ◽  
Support Theory ◽  
Length Data ◽  
Flame Angle

The combined effects of wind velocity and percent slope on flame length and angle were measured in an open-topped, tilting wind tunnel by burning fuel beds composed of vertical birch sticks and aspen excelsior. Mean flame length ranged from 0.08 to 1.69 m; 0.25 m was the maximum observed flame length for most backing fires. Flame angle ranged from −46° to 50°. Observed flame angle and length data were compared with predictions from several models applicable to fires on a horizontal surface. Two equations based on the Froude number underestimated flame angle for most wind and slope combinations; however, the data support theory that flame angle is a function of the square root of the Froude number. Discrepancies between data and predictions were attributed to measurement difficulties and slope effects. An equation based on Byram's convection number accounted for nearly half of the observed variation in flame angle (R2 = 0.46). Byram's original equation relating fireline intensity to flame length overestimated flame length. New parameter estimates were derived from the data. Testing of observed fire behavior under a wider range of conditions and at field scale is recommended.

The effects of wind on the flame characteristics of individual leaves

2011 ◽  
Vol 20 (5) ◽  
pp. 657 ◽  
Author(s):  
Wesley J. Cole ◽  
McKaye H. Dennis ◽  
Thomas H. Fletcher ◽  
David R. Weise
Keyword(s):  
Froude Number ◽  
Flame Length ◽  
Flame Height ◽  
Combustion Model ◽  
Small Scale ◽  
Single Leaf ◽  
Small Branch ◽  
Flame Burner ◽  
Broadleaf Species ◽  
Semi Empirical

Individual cuttings from five shrub species were burned over a flat-flame burner under wind conditions of 0.75–2.80 m s–1. Both live and dead cuttings were used. These included single leaves from broadleaf species as well as 3 to 5 cm-long branches from coniferous and small broadleaf species. Flame angles and flame lengths were determined by semi-automated measurements of video images. Additional data, such as times and temperatures corresponding to ignition, maximum flame height and burnout were determined using video and infrared images. Flame angles correlated linearly with wind velocity. They also correlated with the Froude number when either the flame length or flame height was used. Flame angles in individual leaf experiments were generally 50 to 70% less than flame angles derived from Froude number correlations reported in the literature for fuel-bed experiments. Although flame angles increased with fuel mass and moisture content, they were unaffected by fuel species. Flame lengths and flame heights decreased with moisture contents and wind speed but increased with mass. In most cases, samples burned with wind conditions ignited less quickly and at lower temperatures than samples burned without wind. Most samples contained moisture at the time of ignition. Results of this small-scale approach (e.g. using individual cuttings) apply to ignition of shrubs and to flame propagation in shrubs of low bulk density. This research is one of the few attempts to characterise single-leaf and small-branch combustion behaviour in wind and is crucial to the continued development of a semi-empirical shrub combustion model.

Fuel treatment effects on modeled landscape-level fire behavior in the northern Sierra Nevada

2010 ◽  
Vol 40 (9) ◽  
pp. 1751-1765 ◽  
Author(s):  
Jason J. Moghaddas ◽  
Brandon M. Collins ◽  
Kurt Menning ◽  
Emily E.Y. Moghaddas ◽  
Scott L. Stephens
Keyword(s):  
Sierra Nevada ◽  
Fire Behavior ◽  
Treatment Strategies ◽  
Weather Conditions ◽  
Fire Regimes ◽  
Flame Length ◽  
Fuel Treatment ◽  
Burn Probability ◽  
Pre Treatment ◽  
Landscape Level

Across the western United States, decades of fire exclusion combined with past management history have contributed to the current condition of extensive areas of high-density, shade-tolerant coniferous stands that are increasingly prone to high-severity fires. Here, we report the modeled effects of constructed defensible fuel profile zones and group selection treatments on crown fire potential, flame length, and conditional burn probabilities across 11 land allocation types for an 18 600 ha study area within the northern Sierra Nevada, California. Fire modeling was completed using FlamMap and FARSITE based on landscape files developed with high-resolution aerial (IKONOS) imagery, ground-based plot data, and integrated data from ARCFUELS and the Forest Vegetation Simulator. Under modeled 97th percentile weather conditions, average conditional burn probability was reduced between pre- and post-treatment landscapes. A more detailed simulation of a hypothetical fire burning under fairly severe fire weather, or “problem fire”, revealed a 39% reduction in final fire size for the treated landscape relative to the pre-treatment condition. To modify fire behavior at a landscape level, a combination of fuel treatment strategies that address topographic location, land use allocations, vegetation types, and fire regimes is needed.

Flame characteristics of wind-driven surface fires

1986 ◽  
Vol 16 (6) ◽  
pp. 1293-1300 ◽  
Author(s):  
Ralph M. Nelson Jr. ◽  
Carl W. Adkins
Keyword(s):  
Boundary Layer ◽  
Tilt Angle ◽  
Fire Behavior ◽  
Flame Length ◽  
Fire Intensity ◽  
Square Root ◽  
Pine Needle ◽  
Weather Variables ◽  
Practical Applications ◽  
Surface Fires

Twenty-two fires in a laboratory wind tunnel and 8 field fires were studied with video techniques to determine relationships between their flame characteristics and fire behavior. The laboratory fires were in pine needle fuel beds with and without an overlying stratum of live vegetation. These fuels simulated 2-year roughs in southeastern fuel types. The field bums were in 1- and 2-year roughs in similar fuels. Byram's fire intensity ranged from 98 to 590 kW/m in the laboratory, and from 355 to 2755 kW/m in the field. Flame lengths were proportional to the square root of fire intensity when fuel consumption exceeded 0.5 kg/m2, in agreement with predictions from buoyant flame theory. However, for burns in the needle layer (consumption approximately 0.5 kg/m2), flame lengths were constant at about 0.5 m, regardless of intensity. Similar values were observed on two of the field fires. It is speculated that flame length is limited by a boundary layer pattern for the overall flow, even though the flames themselves did not exhibit boundary layer characteristics. Also, laboratory correlations of flame tilt angle and fire intensity with other fire and weather variables depart from buoyant flame theory. Further study under field conditions is needed before relationships involving flame tilt angle, fire intensity, and wind speed should be used in practical applications.

scholarly journals Sequential and joint hydrogeophysical inversion using a field-scale groundwater model with ERT and TDEM data

2013 ◽  
Vol 17 (10) ◽  
pp. 4043-4060 ◽  
Author(s):  
D. Herckenrath ◽  
G. Fiandaca ◽  
E. Auken ◽  
P. Bauer-Gottwein
Keyword(s):  
Geophysical Data ◽  
Parameter Estimates ◽  
Model Parameters ◽  
Data Sets ◽  
Groundwater Model ◽  
Field Scale ◽  
Geophysical Model ◽  
Time Domain Electromagnetic ◽  
Synthetic Groundwater ◽  
Airborne Geophysical Data

Abstract. Increasingly, ground-based and airborne geophysical data sets are used to inform groundwater models. Recent research focuses on establishing coupling relationships between geophysical and groundwater parameters. To fully exploit such information, this paper presents and compares different hydrogeophysical inversion approaches to inform a field-scale groundwater model with time domain electromagnetic (TDEM) and electrical resistivity tomography (ERT) data. In a sequential hydrogeophysical inversion (SHI) a groundwater model is calibrated with geophysical data by coupling groundwater model parameters with the inverted geophysical models. We subsequently compare the SHI with a joint hydrogeophysical inversion (JHI). In the JHI, a geophysical model is simultaneously inverted with a groundwater model by coupling the groundwater and geophysical parameters to explicitly account for an established petrophysical relationship and its accuracy. Simulations for a synthetic groundwater model and TDEM data showed improved estimates for groundwater model parameters that were coupled to relatively well-resolved geophysical parameters when employing a high-quality petrophysical relationship. Compared to a SHI these improvements were insignificant and geophysical parameter estimates became slightly worse. When employing a low-quality petrophysical relationship, groundwater model parameters improved less for both the SHI and JHI, where the SHI performed relatively better. When comparing a SHI and JHI for a real-world groundwater model and ERT data, differences in parameter estimates were small. For both cases investigated in this paper, the SHI seems favorable, taking into account parameter error, data fit and the complexity of implementing a JHI in combination with its larger computational burden.

Examining fire behavior in mesquite - acacia shrublands

2005 ◽  
Vol 14 (2) ◽  
pp. 131 ◽  
Author(s):  
Tamara J. Streeks ◽  
M. Keith Owens ◽  
Steve G. Whisenant
Keyword(s):  
Flame Temperature ◽  
Fire Behavior ◽  
Fire Spread ◽  
Flame Length ◽  
South Texas ◽  
Fire Intensity ◽  
Rate Of Spread ◽  
Vegetation Shift ◽  
Naturally Occurring ◽  
Behavior Systems

The vegetation of South Texas has changed from mesquite savanna to mixed mesquite–acacia (Prosopis–Acacia) shrubland over the last 150 years. Fire reduction, due to lack of fine fuel and suppression of naturally occurring fires, is cited as one of the primary causes for this vegetation shift. Fire behavior, primarily rate of spread and fire intensity, is poorly understood in these communities, so fire prescriptions have not been developed. We evaluated two current fire behavior systems (BEHAVE and the CSIRO fire spread and fire danger calculator) and three models developed for shrublands to determine how well they predicted rate of spread and flame length during three summer fires within mesquite–acacia shrublands. We also used geostatistical analyses to examine the spatial pattern of net heat, flame temperature and fuel characteristics. The CSIRO forest model under-predicted the rate of fire spread by an average of 5.43 m min−1 and over-predicted flame lengths by 0.2 m while the BEHAVE brush model under-predicted rate of spread by an average of 6.57 m min−1 and flame lengths by an average of 0.33 m. The three shrubland models did not consistently predict the rate of spread in these plant communities. Net heat and flame temperature were related to the amount of 10-h fuel on the site, but were not related to the cover of grasses, forbs, shrubs, or apparent continuity of fine fuel. Fuel loads were typical of South Texas shrublands, in that they were uneven and spatially inconsistent, which resulted in an unpredictable fire pattern.

Behavior of experimental grass fires vs. predictions based on Rothermel's fire model

1977 ◽  
Vol 7 (2) ◽  
pp. 357-367 ◽  
Author(s):  
Richard J. Sneeuwjagt ◽  
William H. Frandsen
Keyword(s):  
Combustion Zone ◽  
Fire Behavior ◽  
Fire Spread ◽  
Flame Length ◽  
Fuel Load ◽  
Physical Parameters ◽  
Rate Of Spread ◽  
Least Squares Fit ◽  
Zone Depth ◽  
Positive Agreement

Fire behavior observations with rates of spread up to 20 m/min (66 ft/min) have been recorded on 40 prescribed grass fires in central Washington and northern California. Physical parameters were also recorded describing the grass fuel array (fuel load, moisture content (≤ 15%), etc.), along with the wind speed (up to 8 km/h) and slope (near zero). These data were sufficient to allow a prediction of the fire spread rate, combustion zone depth, and flame length using the Rothermel fire spread model.A least squares fit of the observed versus the predicted results shows that positive agreement (slope = 1, intercept = 0) is supported for rate of spread. Flame length shows positive agreement for the intercept but not for slope. Combustion zone depth does not show positive agreement for either intercept or slope. The authors attribute the lack of positive agreement to less accurate measurements (ocular estimates) of the flame length and combustion zone depth.

scholarly journals Fire Behavior under a Ceiling in Growing Fire Part 2 Ceiling Jet Velocity and Flame Length

2007 ◽  
Vol 26 (4) ◽  
pp. 479-483
Author(s):  
Takahiro Ishihara ◽  
Hiroyuki Sunahara ◽  
Akimitsu Kikkawa ◽  
Masayuki Mizuno ◽  
Yoshifumi Ohmiya ◽  
...  
Keyword(s):  
Fire Behavior ◽  
Flame Length ◽  
Jet Velocity

scholarly journals A GLOBAL RELATION OF FIRE SMOKE RE-CIRCULATION BEHAVIOUR IN URBAN STREET CANYONS

2015 ◽  
Vol 21 (4) ◽  
pp. 459-469 ◽  
Author(s):  
Longhua Hu ◽  
Xiaochun Zhang ◽  
Wei Zhu ◽  
Zhi Ning ◽  
Fei Tang
Keyword(s):  
Aspect Ratio ◽  
Froude Number ◽  
Wind Velocity ◽  
Street Canyon ◽  
Inertial Force ◽  
Wind Flow ◽  
Street Canyons ◽  
Global Parameter ◽  
Urban Street ◽  
Fire Smoke

Street canyon, formed by buildings along two sides of a road, is an important and ubiquitous architectural element in the metropolises. When a fire occurs in an urban street canyon, a critical serious phenomenon is found to happen where the uprising fire smoke is re-circulated back into the base of the street canyon by the wind flow beyond a critical velocity. Theoretical analysis is derived based on Froude number (Fr), by balancing the inertial force of the wind flow to the buoyancy strength of the fire smoke. It is found that the critical re-circulation wind velocity is proportional to an integrated global parameter . Large Eddy Simulations (LES) are carried out by Fire Dynamics Simulator (FDS). The critical Froude number (Fr) is found to be about 0.7~0.8. The simulation results are well collapsed by the generalized theoretical relation. It is further revealed that the non-dimensional critical re-circulation wind velocity . against aspect ratio of street canyons in the skimming flow pattern (W/H < 1.43) falls into two behavioural regimes, where it firstly increases then remains constant with the increase in street canyon aspect ratio (W/H) with a turning point at W/H = 1. A global non-dimensional relation is finally achieved for the critical re-circulation wind velocity (u), fire heat release rate (Q) and its height (H) to the top of the street canyon as well as the street canyon aspect ratio (W/H).

Exploratory analysis of the variables affecting initial attack hot-spotting containment rate

1991 ◽  
Vol 21 (4) ◽  
pp. 540-544 ◽  
Author(s):  
Peter J. Murphy ◽  
Paul M. Woodard ◽  
Dennis Quintilio ◽  
Stephen J. Titus
Keyword(s):  
Forest Cover ◽  
Black Spruce ◽  
Fire Behavior ◽  
Correlation Coefficients ◽  
Flame Length ◽  
Weather Variables ◽  
Weather Index ◽  
Fire Weather Index ◽  
Rate Of Spread ◽  
Forest Cover Types

Hot-spotting containment rates were determined for 18 fires of various intensities in two common boreal forest cover types: 8 in jack pine (Pinusbanksiana Lamb.) and 10 in black spruce (Piceamariana (Mill.) B.S.P.). Hot-spotting containment rates did not differ significantly between the two cover types. Correlation coefficients showed that hot-spotting containment rates were more closely related to fire behavior than to weather variables measured as part of the Canadian Forest Fire Weather Index System. Hot-spotting containment rate (HCR; m/man-hour) may be predicted based on rate of spread (ROS; m/min) and flame length (FL; m) using the following model: HCR = exp(6.0140 – 0.1830ROS – 0.1201FL). This model was fitted using weighted nonlinear regression; the R2-value was 0.76.

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