Domingos X. Viegas

FireStation — an integrated software system for the numerical simulation of fire spread on complex topography

Abstract A software system aimed at the simulation of fire spread over complex topography is presented. The software implements a semi-empirical model for fire rate of spread, which takes as input local terrain slope, parameters describing fuel properties as well as the wind speed and direction. Fire shape is described with recourse to an ellipse-type model. Two different models are implemented for the simulation of the wind field. Both these models predict wind velocity and direction based on local observation taken at meteorological stations. The whole system was developed under a graphical interface, aiming at a better ease of use and output readability so as to facilitate its application under operational conditions. This work describes the mathematical models employed, provides an overview of the graphical interface and presents the results of some simulations tested against experimental data.

Estimation of shrub height for fuel-type mapping combining airborne lidar and simultaneous color infrared ortho imaging

A fuel-type map of a predominantly shrub-land area in central Portugal was generated for a fire research experimental site, by combining airborne light detection and ranging (LiDAR), and simultaneous color infrared ortho imaging. Since the vegetation canopy and the ground are too close together to be easily discerned by LiDAR pulses, standard methods of processing LiDAR data did not provide an accurate estimate of shrub height. It was demonstrated that the standard process to generate the digital ground model (DGM) sometimes contained height values for the top of the shrub canopy rather than from the ground. Improvement of the DGM was based on separating canopy from ground hits using color infrared ortho imaging to detect shrub cover, which was measured simultaneously with the LiDAR data. Potentially erroneous data in the DGM was identified using two criteria: low vegetation height and high Normalized Difference Vegetation Index (NDVI), a commonly used spectral index to identify vegetated areas. Based on the height of surrounding pixels, a second interpolation of the DGM was performed to extract those erroneously identified as ground in the standard method. The estimation of the shrub height improved significantly after this correction, and increased determination coefficients from R2 = 0.48 to 0.65. However, the estimated shrub heights were still less than those observed in the field.

Slope and wind effects on fire propagation

The vectoring of wind and slope effects on a flame front is considered. Mathematical methods for vectoring are presented and compared to results of laboratory experiments. The concept of multiple standard fire spread directions is presented. The experimental laboratory study, included effects of variable wind velocity and direction on point source flame fronts on a 30° inclined fuel bed.

Prediction of building interference effects on pedestrian level comfort

This paper presents results concerning the interference effect created by two auxiliary buildings located upstream of a recreation area comprising seven pavilions. Both numerical and experimental simulations were used to conduct the analyses, and the experimental and numerical results are compared against each other for vertical velocity profiles at different locations. For the numerical simulation, the RANS equations were solved with the turbulence formulated by the k2e RNG model. For the experimental work, a 1

A Mathematical Model For Forest Fires Blowup

ABSTRACT The very quick fire spread that occurs in some forest fires has been the cause of many fatalities in the past among fire fighters throughout the world. A theoretical model describing the convective interaction between the fire front and the surrounding air is proposed to explain the blowup phenomenon that is observed in nature. This model is based on a set of laboratory experiments of fire blowup in canyons that was used to validate it. The model predicts quite well the general fire behavior observed during two fatal accidents that occurred in the United States and one in Portugal.The very quick fire spread that occurs in some forest fires has been the cause of many fatalities in the past among fire fighters throughout the world. A theoretical model describing the convective interaction between the fire front and the surrounding air is proposed to explain the blowup phenomenon that is observed in nature. This model is based on a set of laboratory experiments of fire blowup in canyons that was used to validate it. The model predicts quite well the general fire behavior observed during two fatal accidents that occurred in the United States and one in Portugal.

Experimental and numerical simulation of flow around two-dimensional hills

Abstract The present work is devoted to the study of the turbulent isothermal flow around two-dimensional sinusoidal hills. In this work, both experimental and numerical approaches were followed. The experimental results were obtained from a simulation carried out in two wind tunnels, for a Reynolds number, based on the hills height, ranging from 1.8 × 10 4 to 2.5 × 10 5 . The results obtained experimentally comprise static wall pressure distributions, velocity profiles at strategic locations and flow visualisation. The algorithm adopted for the numerical simulation is based on a control volume approach applied to a numerically generated boundary fitted grid. The transport equations are solved using the SIMPLEC formulation, and turbulence is modelled with a modified low-Reynolds number k - ϵ model. The comparison between numerical and experimental results shows an overall good agreement.

Wildland Smoke Exposure Values and Exhaled Breath Indicators in Firefighters

Smoke from forest fires contains significant amounts of gaseous and particulate pollutants. Firefighters exposed to wildland fire smoke can suffer from several acute and chronic adverse health effects. Consequently, exposure data are of vital importance for the establishment of cause/effect relationships between exposure to smoke and firefighter health effects. The aims of this study were to (1) characterize the relationship between wildland smoke exposure and medical parameters and (2) identify health effects pertinent to wildland forest fire smoke exposure. In this study, firefighter exposure levels of carbon monoxide (CO), nitrogen dioxide (NO2), and volatile organic compounds (VOC) were measured in wildfires during three fire seasons in Portugal. Personal monitoring devices were used to measure exposure. Firefighters were also tested for exhaled nitric oxide (eNO) and CO before and after their firefighting activities. Data indicated that exposure levels during firefighting activities were beyond limits recommended by the Occupational Exposure Standard (OES) values. Medical tests conducted on the firefighters also indicated a considerable effect on measured medical parameters, with a significant increase in CO and decrease in NO in exhaled air of majority of the firefighters.

Local-scale modelling system to simulate smoke dispersion

The main purpose of this paper is to present a fire behaviour system, developed to estimate fire progression, smoke dispersion and visibility impairment, at a local scale, and to evaluate its performance by comparing results with measurements from the Gestosa 2004 experimental field fires. The system is an improvement of two already available numerical tools, DISPERFIRE (Miranda et al. 1994) and FireStation (Lopes et al. 2002), which were integrated. FireStation is a software system aimed at the simulation of fire spread over complex topography. DISPERFIRE is a real-time system developed to simulate the dispersion in the atmosphere of the pollutants emitted during a forest fire. In addition, a model for the estimation of visibility impairment, based on the relationship between air pollutants concentration and visibility, was included in DISPERFIRE. The whole system was developed using a graphical interface, previously created for FireStation, which provides user-friendliness and easily readable output to facilitate its application under operational conditions. The system was applied to an experimental field fire and the main results were compared with experimental air pollutant concentration measured values. The performance of the model in predicting pollutant concentrations was good, particularly for NO2 and PM10.

Wind tunnel simulation of the flow around two-dimensional hills

Abstract An experimental investigation of flow around two-dimensional hills of sinusoidal cross-section is presented for Reynolds numbers in the range 1.7 × 10 4 −2.4 × 10 5 . The flow around a single hill with four different cross-sections is described by the pressure distribution on the surface of the models and by their topological features. The interaction between two identical hills is studied for varying distances. Pressure and shear-stress distributions on each hill are given, as well as vertical velocity profiles on the tops of the hills. The main properties of the flow obtained by flow visualization are shown.

Study of the jump fire produced by the interaction of two oblique fire fronts. Part 1. Analytical model and validation with no-slope laboratory experiments

When two fires approach each other, convective and radiative heat transfer processes are greatly enhanced. The interaction between two linear fire fronts making an angle θoi between them is of particular interest as it produces a very rapid advance of their intersection point with intense radiation and convection activity in the space between the fire lines. This fire is designated here as a ‘jump fire’ for when the value of θoi is small, the intersection point of the fire lines can reach unusually high rate of spread values that decrease afterwards in the course of time. A very simple analytical model based on the concept of energy concentration between the fire lines is proposed to explain this behaviour, which in large-scale fires can be of great concern to personnel and property safety. Experimental tests performed at laboratory scale on a horizontal fuel bed confirmed the basic assumptions of the model and provide a framework to extend the present analysis to more general conditions, namely to explain the behaviour of real fires. Given the rapid changes in fire behaviour, ‘jump fires’ can be considered as a form of extreme fire behaviour.