In this paper, motion analysis methods based on the moment features and flicker frequency features for early fire flame from ordinary CCD video camera were proposed, and in order to describe the changing of flame and ...In this paper, motion analysis methods based on the moment features and flicker frequency features for early fire flame from ordinary CCD video camera were proposed, and in order to describe the changing of flame and disturbance of non-flame phenomena further more, the average changing pixel number of the first-order moments of consecutive flames has been defined in the moment analysis as well. The first-order moments of all kinds of flames used in our experiments present irregularly flickering, and their average changing pixel numbers of first-order moments are greater than fire-like disturbances. For the analysis of flicker frequency of flame, which is extracted and calculated in spatial domain, and therefore it is computational simple and fast. The method of extracting flicker frequency from video images is not affected by the catalogues of combustion material and distance. In experiments, we adopted two kinds of flames, i. e. , fixed flame and movable flame. Many comparing and disturbing experiments were done and verified that the methods can be used as criteria for early fire detection.展开更多
Full-scale numerical experiments were carried out on the vehicular fire in a long tunnel to study the critical ventilation velocity and back-layer distance with heat release rate of 5, 20 and 100 MW respectively. A co...Full-scale numerical experiments were carried out on the vehicular fire in a long tunnel to study the critical ventilation velocity and back-layer distance with heat release rate of 5, 20 and 100 MW respectively. A computational fluid dynamics (CFD) model of fire-driven fluid flow FDS(Fire Dynamics Simulator) was used to solve numerically a form of the Navier-Stokes equations for fire. The results were compared with the expressions proposed in the literature. A modified equation for the critical ventilation velocity was given to better fit the experimental results. A bi-exponential model that well fitted the numerical experimental results was proposed to describe the relationship between back-layer distance and ventilation velocity.展开更多
Estimation of fire cycle has been conducted by using the negative exponential function as an approximation of time-since-fire distribution of a landscape assumed to be homogeneous with respect to fire spread processes...Estimation of fire cycle has been conducted by using the negative exponential function as an approximation of time-since-fire distribution of a landscape assumed to be homogeneous with respect to fire spread processes. The authors imposed predefined fire cycles on a virtual landscape of 100 cell×100 cell, and obtained a mosaic composing of patches with different stand ages （i.e. time since fire）. Graphical and statistical methods （Van Wagner 1978; Reed et al. 1998） were employed to derive fire cycle from the virtual landscape. By comparing the predefined and the derived fire cycles, the two methods and tested the effects of sample size and hazard of burning （i.e., stand＇s susceptibility to fire in relation to its stand age） were evaluated on fire cycle deviation. The simulation results indicated a minimum sample size of l0 times of the annual burnt area would be required for.partitioning time-since-fire distribution into homogeneous epochs indicating temporal change in fire cycle. Statistically, there was significant difference among the imposed and the derived fire cycle, regardless of sample sizes with or without consideration of hazard of burning. Both methods underestimated the more recent fire cycle without significant difference between them. The results imply that deviation of fire cycle based on time-since-fire distribution warrants cautious interpretation, especially when a landscape is spatially partitioned into small units and temporal changes in fire cycle are involved.展开更多
This paper discusses a method for performing a sensitivity analysis of parameters used in a simplified fire model for temperature estimates in the upper smoke layer during a fire. The results from the sensitivity anal...This paper discusses a method for performing a sensitivity analysis of parameters used in a simplified fire model for temperature estimates in the upper smoke layer during a fire. The results from the sensitivity analysis can be used when individual parameters affecting fire safety are assessed. If the variation of a single parameter is found to have a major impact on fire safety, it may be necessary to conservatively select this parameter in order to incorporate additional safety. We compare fire scenarios in rooms surrounded by lightweight as well as heavy walls in order to investigate which parameters are the most significant in each case. We apply the Sobol method, which is a quantitative method that gives the percentage of the total output variance that each parameter accounts for. The most important parameter is found to be the energy release rate that explains 92% of the uncertainty in the calculated results for the period before thermal penetration （te） has occurred. The analysis is also done for all combinations of two parameters in order to find the combination with the largest effect. The Sobol total for pairs had the highest value for the combination of energy release rate and area of opening, which explains 96% of the uncertainty. After thermal penetration, the energy release rate is still the most important parameter, but now only explains 49% of the variation. The second parameter is the thickness of the surface material, which explains 43%.展开更多
An understanding of soil thermal conductivity after a wildfire or controlled burn is important to land management and post-fire recovery efforts. Although soil thermal conductivity has been well studied for non-fire h...An understanding of soil thermal conductivity after a wildfire or controlled burn is important to land management and post-fire recovery efforts. Although soil thermal conductivity has been well studied for non-fire heated soils, comprehensive data that evaluate the long-term effect of extreme heating from a fire on the soil thermal conductivity are limited. The purpose of this study was to evaluate the long-term impact of fire on the effective thermal conductivity of soils by directly comparing fire-heated and no-fire control soils through a series of laboratory studies. The thermal conductivity was measured for ten soil samples from two sites within the Manitou Experimental Forest, Colorado, USA, for a range of water contents from saturation to the residual degree of saturation. The thermal conductivity measured was compared with independent estimates made using three empirical models from literature, including the Campbell et al. （1994）, CSt~ and Konrad （2005）, and Massman et al. （2008） models. Results demonstrate that for the test soils studied, the thermal conductivity of the fire-heated soils was slightly lower than that of the control soils for all observed water contents. Modeling results show that the Campbell et al. （1994） model gave the best agreement over the full range of water contents when proper fitting parameters were employed. Further studies are needed to evaluate the significance of including the influence of fire burn on the thermal properties of soils in modeling studies.展开更多
Volatiles erupted from large-scale explosive volcanic activities have a significant impact on climate and environmental changes.As an important ecological factor,the occurrence of fire is affected by vegetation cover,...Volatiles erupted from large-scale explosive volcanic activities have a significant impact on climate and environmental changes.As an important ecological factor,the occurrence of fire is affected by vegetation cover,and fire can feed back into both vegetation and climatic change.The causes of fire events are diverse;and can include volcanic eruptions.The amount of charcoal in sediment sequences is related to the frequency and intensity of fire,and hence under good preservation conditions fire history can be reconstructed from fossil charcoal abundance.Until now,little research on the role of fire has been carried out in northeastern China.In this study,through research on charcoal and tephra shards from Gushantun and Hanlongwan,Holocene vegetation change in relation to fire and volcanic events in Jilin,Northeastern China,was investigated.Where tephra shards are present in Gushantun it is associated with low level of both conifers and broadleaved trees,and is also associated with a pronounced charcoal peak.This suggests forest cover was greatly reduced from a fire caused by an eruption of the Tianchi volcano.We also detected one tephra layer in Hanlongwan,which also has the almost same depth with low level forest pollen values and one charcoal peak.This was caused probably by an eruption of the Jinlongdingzi volcano.展开更多
Correlations of fire-induced temperature have been reviewed and revisited.The impact of XY factors,i.e.,the relative locations of the fire source and vent,on temperature models of ceiling-vented compartments could be ...Correlations of fire-induced temperature have been reviewed and revisited.The impact of XY factors,i.e.,the relative locations of the fire source and vent,on temperature models of ceiling-vented compartments could be reflected by the exponents of the two dimensionless terms which represent the ratio of the total energy to energy released through the ceiling vent,and the ratio of the energy lost through the walls to the energy released through the ceiling vent.For fires not located directly below the ceiling vent,the temperature rise was proportional to two thirds of the power of the heat release rate,while for fires immediately beneath this vent,the temperature rise was proportional to four thirds the power of the heat release rate,and was inversely proportional to one sixth the power of the ceiling vent size.展开更多
基金Supported by " Experimental Scale Studies in Smoke Control Strategy in Large Linear Atria in HKSAR" (B Q372)
文摘In this paper, motion analysis methods based on the moment features and flicker frequency features for early fire flame from ordinary CCD video camera were proposed, and in order to describe the changing of flame and disturbance of non-flame phenomena further more, the average changing pixel number of the first-order moments of consecutive flames has been defined in the moment analysis as well. The first-order moments of all kinds of flames used in our experiments present irregularly flickering, and their average changing pixel numbers of first-order moments are greater than fire-like disturbances. For the analysis of flicker frequency of flame, which is extracted and calculated in spatial domain, and therefore it is computational simple and fast. The method of extracting flicker frequency from video images is not affected by the catalogues of combustion material and distance. In experiments, we adopted two kinds of flames, i. e. , fixed flame and movable flame. Many comparing and disturbing experiments were done and verified that the methods can be used as criteria for early fire detection.
基金Supported by the Shanghai Municipal Infor mation Fund Project (2004)
文摘Full-scale numerical experiments were carried out on the vehicular fire in a long tunnel to study the critical ventilation velocity and back-layer distance with heat release rate of 5, 20 and 100 MW respectively. A computational fluid dynamics (CFD) model of fire-driven fluid flow FDS(Fire Dynamics Simulator) was used to solve numerically a form of the Navier-Stokes equations for fire. The results were compared with the expressions proposed in the literature. A modified equation for the critical ventilation velocity was given to better fit the experimental results. A bi-exponential model that well fitted the numerical experimental results was proposed to describe the relationship between back-layer distance and ventilation velocity.
文摘Estimation of fire cycle has been conducted by using the negative exponential function as an approximation of time-since-fire distribution of a landscape assumed to be homogeneous with respect to fire spread processes. The authors imposed predefined fire cycles on a virtual landscape of 100 cell×100 cell, and obtained a mosaic composing of patches with different stand ages （i.e. time since fire）. Graphical and statistical methods （Van Wagner 1978; Reed et al. 1998） were employed to derive fire cycle from the virtual landscape. By comparing the predefined and the derived fire cycles, the two methods and tested the effects of sample size and hazard of burning （i.e., stand＇s susceptibility to fire in relation to its stand age） were evaluated on fire cycle deviation. The simulation results indicated a minimum sample size of l0 times of the annual burnt area would be required for.partitioning time-since-fire distribution into homogeneous epochs indicating temporal change in fire cycle. Statistically, there was significant difference among the imposed and the derived fire cycle, regardless of sample sizes with or without consideration of hazard of burning. Both methods underestimated the more recent fire cycle without significant difference between them. The results imply that deviation of fire cycle based on time-since-fire distribution warrants cautious interpretation, especially when a landscape is spatially partitioned into small units and temporal changes in fire cycle are involved.
文摘This paper discusses a method for performing a sensitivity analysis of parameters used in a simplified fire model for temperature estimates in the upper smoke layer during a fire. The results from the sensitivity analysis can be used when individual parameters affecting fire safety are assessed. If the variation of a single parameter is found to have a major impact on fire safety, it may be necessary to conservatively select this parameter in order to incorporate additional safety. We compare fire scenarios in rooms surrounded by lightweight as well as heavy walls in order to investigate which parameters are the most significant in each case. We apply the Sobol method, which is a quantitative method that gives the percentage of the total output variance that each parameter accounts for. The most important parameter is found to be the energy release rate that explains 92% of the uncertainty in the calculated results for the period before thermal penetration （te） has occurred. The analysis is also done for all combinations of two parameters in order to find the combination with the largest effect. The Sobol total for pairs had the highest value for the combination of energy release rate and area of opening, which explains 96% of the uncertainty. After thermal penetration, the energy release rate is still the most important parameter, but now only explains 49% of the variation. The second parameter is the thickness of the surface material, which explains 43%.
基金supported by the National Science Foundation (NSF), USA (division of graduate education, No.DGE-0638719)
文摘An understanding of soil thermal conductivity after a wildfire or controlled burn is important to land management and post-fire recovery efforts. Although soil thermal conductivity has been well studied for non-fire heated soils, comprehensive data that evaluate the long-term effect of extreme heating from a fire on the soil thermal conductivity are limited. The purpose of this study was to evaluate the long-term impact of fire on the effective thermal conductivity of soils by directly comparing fire-heated and no-fire control soils through a series of laboratory studies. The thermal conductivity was measured for ten soil samples from two sites within the Manitou Experimental Forest, Colorado, USA, for a range of water contents from saturation to the residual degree of saturation. The thermal conductivity measured was compared with independent estimates made using three empirical models from literature, including the Campbell et al. （1994）, CSt~ and Konrad （2005）, and Massman et al. （2008） models. Results demonstrate that for the test soils studied, the thermal conductivity of the fire-heated soils was slightly lower than that of the control soils for all observed water contents. Modeling results show that the Campbell et al. （1994） model gave the best agreement over the full range of water contents when proper fitting parameters were employed. Further studies are needed to evaluate the significance of including the influence of fire burn on the thermal properties of soils in modeling studies.
基金supported by the National Natural Science Foundation of China (Grant No. 41202260)the Chinese Academy of Sciences Strategic Priority Research Program (Grant No. XDA01020304)Overseas Research Scholarship (UK, 2007–2010)
文摘Volatiles erupted from large-scale explosive volcanic activities have a significant impact on climate and environmental changes.As an important ecological factor,the occurrence of fire is affected by vegetation cover,and fire can feed back into both vegetation and climatic change.The causes of fire events are diverse;and can include volcanic eruptions.The amount of charcoal in sediment sequences is related to the frequency and intensity of fire,and hence under good preservation conditions fire history can be reconstructed from fossil charcoal abundance.Until now,little research on the role of fire has been carried out in northeastern China.In this study,through research on charcoal and tephra shards from Gushantun and Hanlongwan,Holocene vegetation change in relation to fire and volcanic events in Jilin,Northeastern China,was investigated.Where tephra shards are present in Gushantun it is associated with low level of both conifers and broadleaved trees,and is also associated with a pronounced charcoal peak.This suggests forest cover was greatly reduced from a fire caused by an eruption of the Tianchi volcano.We also detected one tephra layer in Hanlongwan,which also has the almost same depth with low level forest pollen values and one charcoal peak.This was caused probably by an eruption of the Jinlongdingzi volcano.
基金supported by the Anhui Provincial Natural Science Foundation(1408085MKL94)
文摘Correlations of fire-induced temperature have been reviewed and revisited.The impact of XY factors,i.e.,the relative locations of the fire source and vent,on temperature models of ceiling-vented compartments could be reflected by the exponents of the two dimensionless terms which represent the ratio of the total energy to energy released through the ceiling vent,and the ratio of the energy lost through the walls to the energy released through the ceiling vent.For fires not located directly below the ceiling vent,the temperature rise was proportional to two thirds of the power of the heat release rate,while for fires immediately beneath this vent,the temperature rise was proportional to four thirds the power of the heat release rate,and was inversely proportional to one sixth the power of the ceiling vent size.
