Investigating potential of metal mesh to contain wildfires

This work concerns an exploration of the ability of various metal screens to contain both fire radiant heat flux and firebrand attacks in a wildfire. Wildfires are a growing concern in many parts of the world today. Fighting wildfires is a highly complex and dangerous venture due to their unpredictable nature and fast propagation velocity caused by firebrand attack and radiant heat flux. The unchanged trends of losses indicate the inefficiency of current firefighting techniques and motivate the development of new techniques that are capable of effectively containing wildfires and therefore avoiding losses. Metal meshes are currently being used as flame arrestors and their practice in fire engineering sector has precedent. Metal screens are used with limited applications to protect structures in wildfire-prone areas. The Australian Standard for construction in bushfire-prone areas mandates covering all house openings by metal meshes to minimise the penetration of firebrands into the structures and contain the effect of fire radiation. Likewise, American standards such as the California residential code mandate screens to cover house ventilation openings in order to contain firebrands and flame impingements. Similar recommendations are evident in standards published by the International Code Council (ICC) and the National Fire Protection Association (NFPA) for structures in wildfire-prone areas. All indications imply that metal screens have a potential to contain wildfires propagation mechanisms. Therefore, it is expected that metal screens can be effective as barriers in containing the wildfires. This study aims to investigate the potential of metal screen to be used as wildfire barriers. In this study, the performance of various metal screens to contain both fire radiant heat flux and firebrand attacks was explored in two steps. In the first step, an experimental setup using a light source and UV-visible spectrometer was designed and manufactured to determine the direct radiant flux through square woven wire screens with porosities ranging from 41% to 66%. The tunnel-vision effect of screens was measured and an empirical correlation between screen porosity and the angle of tunnel vision was developed. The results indicate that screens are able to block radiation more than the value suggested by their porosity, and more importantly, screens are more effective for larger radiant sources. Three empirical formulas were presented to calculate the direct radiant heat flux of different size fires through screens. In the second stage, an Ember Shower Simulator (ESS) was developed to study the performance of various metal screens against firebrand attacks. The ESS is capable of generating firebrands from various types of vegetation and performing experiments with low porosity screens at relatively high wind speeds. In a series of experiments, the effects of screen opening size, opening shape, wire diameter, screen manufacturing type and orientation of screens with respect to the firebrand flow on their performance against a Eucalyptus leaf firebrand shower were investigated. Further in this study, the combined effect of screen with different opening sizes and a buffer zone behind the screen was examined. Two important mechanisms of firebrands passing through the screens were identified. Some firebrands shatter into smaller firebrands called secondary firebrands and then pass the screen opening. Some others that are less vulnerable keep burning behind the screen to reduce their size and pass through the screen opening. The screen opening size and wire diameter were found to have a great effect on the shattering intensity and the size of firebrands leaving the screen. Flat screens had a lower shattering intensity with respect to woven screens. An inclined screen increased the retention of firebrands behind screens in comparison with a vertical screen. This study could confirm that buffer zones are effective in improving the protection of objects shielded by a screen against firebrands. The experiments showed a relation between screen opening size and the size of the buffer zone as more firebrands quenched within the buffer zone for smaller opening size screens. It was found that the combination of buffer zone and screen remarkably reduced the number and size of firebrands on the fuel bed. As a result, the number of firebrand-induced ignitions significantly decreases in comparison with the condition that the screen is absent. A discussion on the effectiveness of screens to contain the two propagation mechanisms is provided. Based on the discussion, it was found that metal screens are effective in containing the fire radiant heat flux and to considerably reduce the safety distance from a fire. The screens are efficient in substantially mitigating firebrand showers when a relatively short buffer zone is established. The results imply that screens may be capable of eliminating the risks of both firebrand attacks and radiant heat flux if an appropriate buffer zone is established

18th Australasian Fluid Mechanics Conference (AFMC 2012)

Smoke and toxic gases emitted from chimneys present health hazard. Their concentration should be minimised before reaching the ground. The wind lowers the concentration before it reaches the surface. However, heavier than air toxic gases flow downward which is particularly problematic in the case of low wind speeds in high-density populated areas. Two effective solutions are to extend the height of the chimney or to employ a filter but generally these solutions are not practical or economical for residential applications. An innovative low-cost chimney cap is proposed to dilute toxic gases within the chimney before ejection. The configuration of the cap is inspired from chambers which are currently used to generate fire-whirl in the laboratory. The cap consists of two identical half cylinders which are placed off-centre at the top of the chimney. The previous experiments indicate that the entrained air swirls around the central vertical axis of the chamber and generates a whirling motion. The chimney discharge and the exhaust concentration are computed by modelling the cap. The computational results indicate that such a configuration not only is able to reduce the concentration of the discharge, but also is able to increase the discharge at low wind speeds

2012 Southern Regional Engineering Conference (SREC 2012)

Bushfires have very devastating effects on human life, economy and environment. Current techniques and approaches are capable of extinguishing fires with intensity less than 2.5 MW of heat per fire front. However, the heat intensity of a large fire could reach well above 100 MW/m. Fire propagates through direct flame contact, radiation and ember attack. A successful technique to contain intense bushfires should be able to deal with all three modes of fire propagation. This work investigates prospective approaches to contain intense bushfires. Preliminary study indicates that using metal mesh has potential. There have been several reports on the News that metal meshes could prevent bushfire from propagation. A recent study reveals that a mesh with porosity of 25% is able to block 89% of direct heat flux of a large bushfire. Some applications such as Bunsen burners indicate its effectiveness against direct flame contact. Their values against ember attacks are well known in Australia and other countries. Australian Standard for construction of buildings in bushfire-prone area [AS 3959-2009] recommends that mesh should be applied on all openable windows, gutters and external doors with a maximum aperture size of 1.8 mm. However, this study shows further detail investigation is required in order to minimize the wind force

A novel ember shower simulator for assessing performance of low porosity screens at high wind speeds against firebrand attacks

Previous studies have shown the effectiveness of low porosity and double-layer screens against radiant heat flux from fires. The performance of screens against firebrand attack is also required to be assessed prior to making a decision on their possible application in wildland fire prone areas. The available laboratory-scale devices simulate firebrands at wind speeds less than those of severe firebrand attacks. A relatively low cost, laboratory-scale fire ember shower simulator has been designed and manufactured in-house. The simulator is able to assess the performance of low porosity screens at high wind speeds without any reverse flow and possible consequent safety hazards and offers reasonable control over the size and mass of the generated firebrands

Investigating potential of metal mesh to contain wildfires

This work concerns an exploration of the ability of various metal screens to contain both fire radiant heat flux and firebrand attacks in a wildfire. Wildfires are a growing concern in many parts of the world today. Fighting wildfires is a highly complex and dangerous venture due to their unpredictable nature and fast propagation velocity caused by firebrand attack and radiant heat flux. The unchanged trends of losses indicate the inefficiency of current firefighting techniques and motivate the development of new techniques that are capable of effectively containing wildfires and therefore avoiding losses. Metal meshes are currently being used as flame arrestors and their practice in fire engineering sector has precedent. Metal screens are used with limited applications to protect structures in wildfire-prone areas. The Australian Standard for construction in bushfire-prone areas mandates covering all house openings by metal meshes to minimise the penetration of firebrands into the structures and contain the effect of fire radiation. Likewise, American standards such as the California residential code mandate screens to cover house ventilation openings in order to contain firebrands and flame impingements. Similar recommendations are evident in standards published by the International Code Council (ICC) and the National Fire Protection Association (NFPA) for structures in wildfire-prone areas. All indications imply that metal screens have a potential to contain wildfires propagation mechanisms. Therefore, it is expected that metal screens can be effective as barriers in containing the wildfires. This study aims to investigate the potential of metal screen to be used as wildfire barriers. In this study, the performance of various metal screens to contain both fire radiant heat flux and firebrand attacks was explored in two steps. In the first step, an experimental setup using a light source and UV-visible spectrometer was designed and manufactured to determine the direct radiant flux through square woven wire screens with porosities ranging from 41% to 66%. The tunnel-vision effect of screens was measured and an empirical correlation between screen porosity and the angle of tunnel vision was developed. The results indicate that screens are able to block radiation more than the value suggested by their porosity, and more importantly, screens are more effective for larger radiant sources. Three empirical formulas were presented to calculate the direct radiant heat flux of different size fires through screens. In the second stage, an Ember Shower Simulator (ESS) was developed to study the performance of various metal screens against firebrand attacks. The ESS is capable of generating firebrands from various types of vegetation and performing experiments with low porosity screens at relatively high wind speeds. In a series of experiments, the effects of screen opening size, opening shape, wire diameter, screen manufacturing type and orientation of screens with respect to the firebrand flow on their performance against a Eucalyptus leaf firebrand shower were investigated. Further in this study, the combined effect of screen with different opening sizes and a buffer zone behind the screen was examined. Two important mechanisms of firebrands passing through the screens were identified. Some firebrands shatter into smaller firebrands called secondary firebrands and then pass the screen opening. Some others that are less vulnerable keep burning behind the screen to reduce their size and pass through the screen opening. The screen opening size and wire diameter were found to have a great effect on the shattering intensity and the size of firebrands leaving the screen. Flat screens had a lower shattering intensity with respect to woven screens. An inclined screen increased the retention of firebrands behind screens in comparison with a vertical screen. This study could confirm that buffer zones are effective in improving the protection of objects shielded by a screen against firebrands. The experiments showed a relation between screen opening size and the size of the buffer zone as more firebrands quenched within the buffer zone for smaller opening size screens. It was found that the combination of buffer zone and screen remarkably reduced the number and size of firebrands on the fuel bed. As a result, the number of firebrand-induced ignitions significantly decreases in comparison with the condition that the screen is absent. A discussion on the effectiveness of screens to contain the two propagation mechanisms is provided. Based on the discussion, it was found that metal screens are effective in containing the fire radiant heat flux and to considerably reduce the safety distance from a fire. The screens are efficient in substantially mitigating firebrand showers when a relatively short buffer zone is established. The results imply that screens may be capable of eliminating the risks of both firebrand attacks and radiant heat flux if an appropriate buffer zone is established

Effective factors on the performance of woven wire screens against leaf firebrand attacks

Firebrand spotting is the dominant wildfire propagation mechanism. The use of wire screens to prevent firebrand entry into structures is recommended or mandated by many standards. The existing standards address only one feature of screens which is opening size. This experimental study aims to explore several other factors that may influence the performance of wire screens and may need to be incorporated in codes and standards development process for structures located in wildfire prone areas. The results demonstrate a previously unreported shattering mechanism in the case of Eucalyptus populnea (from the Myrtle family) leaf firebrands under a moderate wind speed of 14.5 m/s. The results also show that screen porosity, screen type and wind speed would be appropriate to be addressed in developing standards, but there is no need for concern about screen orientation as long as the screen is placed perpendicular to the wind direction during the experiment

18th Australasian Fluid Mechanics Conference (AFMC 2012)

Combined-gas and steam-turbine power plants have become popular in recent years for distributed power generation and heat production. The optimal thermodynamic and economical design of these plants requires the study of their main components, which are the gas turbine, the steam turbine and the Heat Recovery Steam Generator (HRSG). The HRSG is a heat exchanger that recovers heat from the gas turbine cycle and produces steam and/or hot water, either to be used in a downstream steam cycle or to feed industrial/civil utilities. Some HRSGs include Supplementary Firing (SF) which are additional burners providing additional energy at lower capital costs. However, the supplementary burners cause pressure drops through the duct burner bars which makes the gas turbine to be exhausted at higher pressures. The gas pressure drop should be limited, as previous works show each additional 10 millibars gas pressure drop in the HRSG decreases the gas turbine power output by about 1%. In this work, pressure drop in an off-Supplementary Firing burner of HRSGs has been simulated using two- and three-dimensional models. Simulations indicate that the pressure drop increases with the temperature of the flow entering the burner section. The computational results show very good agreement with semi-empirical results

Evaluating the correlation of blood pressure and pulse rates of firefighters with their sociodemographic characteristics during a fire and rescue training

Introduction: Cardiac strain has become a prevalent cause of firefighters’ death. Standards and regulations set forth a framework to monitor the cardiovascular fitness of firefighters, encourage fitness and create a pathway to diagnosis or detection of disorders. The effectiveness of these standards relies on continuous evaluation of firefighters’ health and updating the protocols. Methods: This study intended to assess the physiological response of 172 firefighters in the middle east for the first time and considered the effect of body mass index, age, gender, and seasonal ambient temperature on their responses before and after a fire and rescue training. The end results should compile the behavioral patterns of firefighters from the region and help authorities to update current health monitoring standards for firefighters accordingly. Blood pressure, heart and respiratory rates were sampled for participants after one minute after when training finished. Non-Parametric statistical analysis was conducted using Nonparametric Spearman rank correlation coefficients and Kruskal-Wallis H- test to evaluate the correlation of age, gender, BMI, and seasonal temperature with participant’s physiological response. Results: This study found obesity in 20% of the sampled population with more cases among male participants. Also, in this study, the hypertension prevalence ratio found as 19.8% at baseline and 26.7% in post-training measurements. Conclusion: This study could confirm that body mass index and seasonal ambient temperature affect blood pressure, heart and ventilation rates. Heart rate significantly changes with ambient temperature. Also, the results found the gender of participants affects all physiological responses, especially heart rate

Global investments in pandemic preparedness and COVID-19: development assistance and domestic spending on health between 1990 and 2026

Background The COVID-19 pandemic highlighted gaps in health surveillance systems, disease prevention, and treatment globally. Among the many factors that might have led to these gaps is the issue of the financing of national health systems, especially in low-income and middle-income countries (LMICs), as well as a robust global system for pandemic preparedness. We aimed to provide a comparative assessment of global health spending at the onset of the pandemic; characterise the amount of development assistance for pandemic preparedness and response disbursed in the first 2 years of the COVID-19 pandemic; and examine expectations for future health spending and put into context the expected need for investment in pandemic preparedness. Methods In this analysis of global health spending between 1990 and 2021, and prediction from 2021 to 2026, we estimated four sources of health spending: development assistance for health (DAH), government spending, out-of-pocket spending, and prepaid private spending across 204 countries and territories. We used the Organisation for Economic Co-operation and Development (OECD)'s Creditor Reporting System (CRS) and the WHO Global Health Expenditure Database (GHED) to estimate spending. We estimated development assistance for general health, COVID-19 response, and pandemic preparedness and response using a keyword search. Health spending estimates were combined with estimates of resources needed for pandemic prevention and preparedness to analyse future health spending patterns, relative to need. Findings In 2019, at the onset of the COVID-19 pandemic, US$9·2 trillion (95$7·3 trillion (95% UI 7·2–7·4) in 2019; 293·7 times the $24·8 billion (95$43·1 billion in development assistance was provided to maintain or improve health. The pandemic led to an unprecedented increase in development assistance targeted towards health; in 2020 and 2021, $1·8 billion in DAH contributions was provided towards pandemic preparedness in LMICs, and$37·8 billion was provided for the health-related COVID-19 response. Although the support for pandemic preparedness is 12·2% of the recommended target by the High-Level Independent Panel (HLIP), the support provided for the health-related COVID-19 response is 252·2% of the recommended target. Additionally, projected spending estimates suggest that between 2022 and 2026, governments in 17 (95% UI 11–21) of the 137 LMICs will observe an increase in national government health spending equivalent to an addition of 1% of GDP, as recommended by the HLIP. Interpretation There was an unprecedented scale-up in DAH in 2020 and 2021. We have a unique opportunity at this time to sustain funding for crucial global health functions, including pandemic preparedness. However, historical patterns of underfunding of pandemic preparedness suggest that deliberate effort must be made to ensure funding is maintained