Mechanisms Of Fire Spread Research Articles

The effect of fuel moisture content on the spread rate of forest fires in the absence of wind or slope

Most studies on the effect of fuel moisture content (FMC) on forest fire behaviour focus on dead fuel moisture; mechanisms of fire spread in live vegetation are considered to remain unexplained by current theory and modelling. In this work, an empirical model for quantifying the effect of FMC on the ratio between spread rate and fuel bed height of fires in the absence of wind or slope was proposed. The model was fitted using data from laboratory experiments, carried out in fuel beds representative of natural litter and shrubland fuel complexes in a wide range of FMC (6–179%), and tested against data from field experiments and wildfires. The pattern of spread rate variation with FMC, namely its reduced rate for values above ~80%, was explained by the ratio between fuel low heat content and energy required for ignition.

복수 구획간의 수평 연소 확대 메카니즘에 관한 연구

복수 구획간의 수평 연소 확대 메카니즘에 관한 연구

Full-Scale Experimental Investigation to Quantify Building Component Ignition Vulnerability from Mulch Beds Attacked by Firebrand Showers

Structure ignition by wind-driven firebrand showers is an important fire spread mechanism in large outdoor fires. Experiments were conducted with three common mulch types (shredded hardwood mulch, Japanese Cypress wood chips, and pine bark nuggets) placed adjacent to realistic-scale reentrant corners. In the first series of experiments, mulch beds were placed adjacent to a re-entrant corner constructed with wood studs and lined with oriented strand board (OSB) as the sheathing. The premise behind conducting experiments with no siding treatments applied was predicated on the notion that bare OSB mulch contact would be a worst-case scenario, and therefore, a wall assembly in the most vulnerable state to mulch ignition. In the second series of experiments, vinyl siding was applied to the re-entrant corner assemblies (wood studs/OSB/moisture barrier/vinyl siding), and the influence of vertical separation distance (102 mm or 203 mm) on wall ignition from adjacent mulch beds was determined. The vertical separation distance was maintained by applying gypsum board to the base of the re-entrant corner. The siding itself did not influence the ignition process for the mulch beds, as the mulch beds were the first to ignite from the firebrand showers. In all experiments, it was observed that firebrands produced smoldering ignition in the mulch beds, this transitioned to flaming ignition, and the re-entrant corner assembly was exposed to the flaming mulch beds. With no siding treatments applied, the flaming mulch beds ignited the re-entrant corner, and ignition was observed to propagate to the back side of re-entrant corner assembly under all wind speeds (6 m/s to 8 m/s). With respect to the re-entrant corners fitted with vinyl siding, the mulch type, vertical separation distance, and wind speed were important parameters as to whether flaming ignition was observed to propagate to the back-side of a reentrant corner assembly. Mulches clearly pose an ignition hazard to structures in large outdoor fires.

Optimizing the Coupling of a Firebrand Generator to a Horizontal Wind Tunnel

Australia is considered as the most fire-prone country in the world. Spotting ignition by lofted firebrands is the main mechanism of fire spread. Many experimental studies have been conducted to evaluate the effect of the firebrand attacks on structures and to identify possible solutions. The experimental facility consists of a firebrand generator coupled to a wind tunnel. The wind speed in the firebrand generator is relatively low, in order to assure a quality continuous flow of glowing firebrands. On the contrary, the wind speed in the wind tunnel is high to duplicate actual firebrand attacks. Previous works show a highly turbulent region above the entrance of firebrands to the wind tunnel which is formed because of the velocity difference and penetration of firebrand entrance hose into the wind tunnel. The penetration is required to provide a uniform firebrand distribution along the height of the test section. In this computational work, the influence of the height of the entrance hose, its orientation respect to the tunnel and the distance between the coupling port and the test section are analyzed. The optimized results are presented and discussed for a variety of wind speeds within the wind tunnel and the firebrand generator.

Investigation on an Integrated Evacuation Route Planning Method Based on Real-Time Data Acquisition for High-Rise Building Fire

Evacuation of occupants in high-rise buildings is one of the most important tasks when the building is subjected to a significant level of fire threat. Since the mechanism of fire spread is too complicated for the trapped people to determine the evacuation route, a real-time evacuation route planning method is needed for rescue and safety management. In this paper, an integrated real-time evacuation route planning method for high-rise building fires is proposed. This method is composed of real-time data acquisition, risk distribution calculation, and evacuation route formulation. The real-time data acquisition process is achieved by using the sensor system and the wireless data transmission system, the calculation of risk distribution is based on the risk assessment of casualties, and the formulation of evacuation route is based on the fast marching level set method. To demonstrate the presented method, a sample building under an assumed fire is used for numerical investigation, and a real building model is used for experimental investigation. The results show that this method can evaluate the fire status and formulate evacuation strategies instantly in high-rise building fire. The risk distribution and the evacuation route of the building fire can be intuitively displayed. This method can be used in practical applications and will be an important technical basis for the program development of rescue and evacuation.

Mechanism of fire spread on facades and the new Technical Report of EOTA “Large-scale fire performance testing of external wall cladding systems”

In many European countries it is a requirement to carry out large-scale tests using full-scale test rigs to evaluate the fire performance of external wall cladding systems. The reason for this is that the laboratory test methods (e.g. those according to EN 13501-1 or national standards) used for the classification of the reaction to fire performance of building materials are unsuitable for a realistic simulation of the fire performance of external wall cladding systems. The following reasons can be named: – Sample measurements are too low – Fire conditions are too low compared to the effect of fire on a facade due to flames venting from the window of a room with a fully developed fire – Limited reproduction of facade structures that may promote the spread of fire, such as the suction effect in the air space of ventilated external wall cladding – No ability to consider detailed formations, such as those around jambs in external wall openings or base finishings – No ability to consider structural fire safety measures. For these reasons it was discussed, shortly after the introduction of the European classification system for the reaction to fire performance of building materials in 2002, to include an additional test method for external wall cladding systems. The Fire Regulators Group (FRG), which advises the European Commission (EC) on fire safety matters, even created a working group to deal with this. Its mission was to create an appropriate standardisation mandate for CEN. After intensive preparations it presented the draft mandate in autumn 2004 [1], which contained the key points for the test standard to be developed by CEN. In addition to this work in the FRG, detailed justifications explaining why such a full-scale test method was necessary for the evaluation of the fire performance of external wall cladding systems were submitted to the services of the European Commission by several Member StateMember States of the EU. Despite this, the EC decided in autumn 2005 not to issue this standardisation mandate. The reason was submitted to the Standing Committee on Construction at the EC in the document CONSTRUCT 05/716rev.1 [2]. However, since the European Organisation for Technical Assessment (EOTA) published or was working on a series of guidelines for the granting of European Technical Approvals (ETA) for construction kits for the fabrication of external wall cladding systems at the time, EOTA received through [2] the task of developing a suitable test method for these products. For this purpose a small working group of representatives from different European approval bodies was formed.

A Study of Thermal Modeling for Fire Spread Mechanism in Residential Building

This study is intended to present a computational thermal model for a residential building. As the Performance Based Design is more popular, fire-intensity and fire-load have turned out to be very important factors for building design and can be predicted through some computational work. To predict and estimate the fire properties of a residential fire, we made some numerical models of combustibles and residential building. In a bid to validate the estimate values, computational analysis results from numerical models were compared with real fire tests. For computational analysis, the Fire Dynamics Simulator was used with Large Eddy Simulation model for turbulence. Consequently, fire-intensity was well predicted and flash-over of rooms were successfully estimated.

A Study of Thermal Modeling for Fire Spread Mechanism in Residential Building

This study is intended to present a computational thermal model for a residential building. As the Performance Based Design is more popular, fire-intensity and fire-load have turned out to be very important factors for building design and can be predicted through some computational work. To predict and estimate the fire properties of a residential fire, we made some numerical models of combustibles and residential building. In a bid to validate the estimate values, computational analysis results from numerical models were compared with real fire tests. For computational analysis, the Fire Dynamics Simulator was used with Large Eddy Simulation model for turbulence. Consequently, fire-intensity was well predicted and flash-over of rooms were successfully estimated.

Firebrands and spotting ignition in large-scale fires

Spotting ignition by lofted firebrands is a significant mechanism of fire spread, as observed in many large-scale fires. The role of firebrands in fire propagation and the important parameters involved in spot fire development are studied. Historical large-scale fires, including wind-driven urban and wildland conflagrations and post-earthquake fires are given as examples. In addition, research on firebrand behaviour is reviewed. The phenomenon of spotting fires comprises three sequential mechanisms: generation, transport and ignition of recipient fuel. In order to understand these mechanisms, many experiments have been performed, such as measuring drag on firebrands, analysing the flow fields of flame and plume structures, collecting firebrands from burning materials, houses and wildfires, and observing firebrand burning characteristics in wind tunnels under the terminal velocity condition and ignition characteristics of fuel beds. The knowledge obtained from the experiments was used to develop firebrand models. Since Tarifa developed a firebrand model based on the terminal velocity approximation, many firebrand transport models have been developed to predict maximum spot fire distance. Combustion models of a firebrand were developed empirically and the maximum spot fire distance was found at the burnout limit. Recommendations for future research and development are provided.

Risk and Behavior of Fire Spread in A Densely-built Urban Area

A fire staring in a densely-built urban area easily spreads to adjacent buildings. In the case of large earthquakes in which multiple fires may break out simultaneously, the spread of such fires may overwhelm the ability of firefighters and damage large areas. In this study, fire spread simulations were carried out in order to investigate behavior of fire spread in Kyoto Higashiyama area, one of the representatives of densely-built urban areas in Japan. A physics-based model was used in which the following mechanisms of fire spread are considered: thermal radiation heat transfer from fire-involved buildings; elevation of ambient temperature by wind-blown fire plumes; and spotting ignition by firebrands. The risk of fire spread was also analyzed by the Monte Carlo method to evaluate the expected magnitude of loss. The effect of uncertainty of the location of fire origin and the weather conditions was investigated.

Comparison of spatially explicit forest landscape fire disturbance models

Comparisons of model behaviors are an efficient way of understanding the differences amongst various models and thus providing guidance to model users for selecting suitable models for their own purposes. This study focuses on a comparison of the most commonly used fire spread algorithms used in scenario fire regime models. This paper provides an overview of fire regime modeling and describes a simulation model, Ecological Disturbance Model, as a simulation shell for such a comparison using the Fort A La Corne forest area in central Saskatchewan, Canada, as the study area. Simulation results suggested that for a fire scenario modeling approach, various fire spread algorithms such as DISPATCH, percolation, and cellular automata (CA) may not result in significant differences between user-defined and simulated fire frequencies; however, significant differences in simulated forest dynamics could result when using different fire spread algorithms. The simulation results from DISPATCH and CA are more similar than those from the percolation algorithm; however, the latter appeared to be a better representative of observed fire spread processes due to its underlying assumption of fire spread mechanisms. Simulation results also suggested that the fire spread algorithms that replicate four or eight direction fire spread in percolation and CA will not make a significant difference in simulated fire regimes or forest dynamics. It is thus recommend that using simulation shells as a tool to take alternative assumptions or models into account to narrow down the uncertainty parameters and avoid the paradoxes in the modeling of natural resource management.

Application of a nonlinear evolution model to fire propagation

The numerical simulation of fire in forest has been an important objective in recent researches, The rate of spread and shape of a forest fire front is af8ecte.d by many factors. The most important of these are as follows: fuel type and moisture content, wind velocity and variability, forest topography, fire spread mechanism, fuel continuity and the amount of spotting (cf.[ l-21). The development of Geographic Information Systems allows the incorporation of these data to the developed models, The first models took into account constant factors, continuous uniform fuel type, constant wind velocity, moisture and slope. Under these conditions, a fire ignited at a single point reaches a quasi-steady state and progresses toward the down wind direction and expands at a constant rate. These data cannot give precise predictions under variable conditions but are very useful in order to the intuition of the fire controller. Models capable of being incorporated into the computer simulations of fires under variable conditions have been developed, based on cellular automata (cf. [3-7]), and stochastic process [8]. These models can give useful indicators as to fire behavior under such conditions. Combustion phenomena has been extensively studied [9], unsteady flame propagation has been analyzed [lo]. Models based on combustion theories are very difficult to develop because of the diversity of the fuel type and varied chemical composition within a given fuel type. Because of the complexity of the problem, models based rigorously on combustion theory have not been completely developed. In this preliminary work, a first attempt is done to design a computer code for numerical simulation of forest fire spread in landscapes. Basically a convection-diffusion model for temperature and a mass-consistent model for wind field simulation will be assumed. A two-steps chemical mechanism is simplified in order to obtain the heat source. This proposed 2-D model take into account the convection phenomena due to temperature gradients in vertical direction. A numerical solution of the former model is presented using a finite difference method together with the study of stability. This numerical method is contrasted with an adaptive finite element method using reflnementiderefinement techniques (cf. [ 1 1 - 143).

Landscape dynamics in crown fire ecosystems

Crown fires create broad-scale patterns in vegetation by producing a patch mosaic of stand age classes, but the spread and behavior of crown fires also may be constrained by spatial patterns in terrain and fuels across the landscape. In this review, we address the implications of landscape heterogeneity for crown fire behavior and the ecological effects of crown fires over large areas. We suggest that fine-scale mechanisms of fire spread can be extrapolated to make broad-scale predictions of landscape pattern by coupling the knowledge obtained from mechanistic and empirical fire behavior models with spatially-explicit probabilistic models of fire spread. Climatic conditions exert a dominant control over crown fire behavior and spread, but topographic and physiographic features in the landscape and the spatial arrangement and types of fuels have a strong influence on fire spread, especially when burning conditions (e.g., fuel moisture and wind) are not extreme. General trends in crown fire regimes and stand age class distributions can be observed across continental, latitudinal, and elevational gradients. Crown fires are more frequent in regions having more frequent and/or severe droughts, and younger stands tend to dominate these landscapes. Landscapes dominated by crown fires appear to be nonequilibrium systems. This nonequilibrium condition presents a significant challenge to land managers, particularly when the implications of potential changes in the global climate are considered. Potential changes in the global climate may alter not only the frequency of crown fires but also their severity. Crown fires rarely consume the entire forest, and the spatial heterogeneity of burn severity patterns creates a wide range of local effects and is likely to influence plant reestablishment as well as many other ecological processes. Increased knowledge of ecological processes at regional scales and the effects of landscape pattern on fire dynamics should provide insight into our understanding of the behavior and consequences of crown fires.

Shapes of simulated fires in discrete fuels

Simulation models are used to examine the possible effects of discrete fuel distributions and of several fire-spread mechanisms on fire shapes. Two postulated fire spread mechanisms —heat accumulation and flame contact—are shown to yield near-ellipses in continuous fuels, but a wide range of shapes in discrete and very patchy fuels. The alternative shapes include ovoids, “tear-drop” (with the ignition point at varying positions on the major axis), and straight lines. Simulated fires in discrete, patchy fuels are less regular in shape than in uniform and continuous fuels and show little or no backburning. The results may explain certain observed differences between wildfire shapes that occur in different environments and at different burning intensities.

Fire spread mechanisms along steel cylinders in high pressure oxygen

Fire spread along steel cylinders in high pressure oxygen has been studied. Upward and downward fire spread experiments were conducted in a cylindrical, high pressure oxygen chamber of about 2.5 × 10 7 mm 3 capacity. The fire spread phenomena were recorded photographically and by television and analyzed. Based on the experimental results, the mechanisms of fire spread are discussed. Fire spread was found to depend on the test piece diameter, oxygen pressure, and spread direction. Upward fire spread was rather steady, although periodic detachment of molten iron oxide mass and cyclic variation in spread rate occurred. Two different modes were observed of downward fire spread. One was observed at a lower oxygen pressure. The molten iron oxide mass detached from the burning test piece end to become a droplet, so that the mode of fire spread in this case was much the same as that of upward fire spread. The other was observed at a higher oxygen pressure. The molten mass flowed down along the test piece. The fire spread in this case was accelerative and its rate was much larger than that in the aforementioned cases. An analysis for steady fire spead has been performed by considering heat transfer from the burning region to the unburned solid iron. It was shown that the ratio of the molten mass surface areas to the test piece cross section area is an important parameter for discussing the fire spread mechanisms. Based on the dependence of this ratio on the oxygen pressure or test piece diameter, it was inferred that the spread rate depends on the rate of oxygen adsorption at the molten mass surface and convective heat transfer at the molten-solid boundary.

Mechanisms of fire spread

Mechanisms involved in many types of fire spread are described in a manner that sacrifices accuracy for the purpose of emphasizing general aspects of the underlying heat-transfer, fluid-flow and chemical-kinetic phenomena. Consideration is given to conditions for transition from one mode of propagation to another. Research on fire spread has been pursued intensively in recent years, and in the present contribution at attempt is made to provide a framework within which various studies can be placed. Entries to current literature are provided. Areas of apparent importance that do not seem to have been emphasized are suggested.