INTRODUCTION TO FIRE DYNAMICS DRYSDALE EPUB
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This paper focuses on the flammability and fire hazards of photovoltaic modules. Bench-scale experiments based on polycrystalline silicon PV modules have been conducted using a cone calorimeter.
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Several parameters including ignition time tig , mass loss, heat release rate HRR , carbon monoxide CO and carbon dioxide CO2 concentration, were investigated. The fire behaviours, fire hazards and toxicity of gases released by PV modules are assessed based on experimental results. This work will lead to better understanding on photovoltaic fires and how to help authorities determine the appropriate fire safety provisions for controlling photovoltaic fires.
Keywords: photovoltaic fires, flammability, fire hazards, cone calorimeter 1.
Introduction Solar energy is one of the most promising renewable energy resources. Similar projects were also carried out in other countries such as Germany, Japan and China. Meanwhile, building integrated photovoltaic BIPV is in rapid development. As an emerging technology installed on residential and commercial buildings, the security of BIPV is a prime concern. Therefore, it should be ensured that photovoltaic modules will not cause any damage to the buildings nor harm to the residents.
Original Research ARTICLE
However, fires in residential and commercial buildings are relatively common. Photovoltaic arrays mounted on buildings might worsen the pre-existing level of fire hazards. This is because photovoltaic PV modules could modify the propagation of fire outside or through the building.
It might interfere with the smoke and venting system, which will hamper the fire extinction operations as well as induce a further hazard through electrical shock for firefighters. Moreover, many of the PV systems on buildings are of sufficiently high voltages to Volts DC [ 2 , 3 ], which means that they may start a fire themselves.
PV modules are closely related to lives and properties. Consequently, there have been lots of efforts to establish rigorous safety standards to mitigate the potential risks.
These two standards have similar requirements, including fire-resistant, hot spot, and temperature tests.
They both have effectively restricted designs that minimize the spread of fires. Italian National Fire Services Guidelines provide a procedure to assess and alleviate fire risks caused by PV arrays located on buildings [ 7 ].
Article These standards or guidelines are still being improved by many researchers. For example, the causes of PV fires have been investigated by Wohlgemuth et al. They found that hot spots, high series resistance and arcing are three typical ways that a module can be overheated to start a sustainable fire within the module.
Even with all these efforts, severe building fires involving PV arrays have been reported in the past few years, such as the fire in LaFarge WI, America in May , of which the big fire began with a small fire from the rooftop PV system. As a result, it is still worthwhile to study the flammability and fire hazards of PV modules in depth, which is the motivation of the current study.
As PV arrays are often sloped, foam or powder could simply slide off. Moreover, many PV systems are of high voltages to Volts DC , which are rather life-threatening.
Role of buoyant flame dynamics in wildfire spread
During a fire event, it is not possible to turn off the whole photovoltaic power system in order to guarantee that all the components are de-energized. In fact, these systems are alive as long as there is light. Thus water jets are also of limited usage in such situations because of their conductibility. The structure and intermittency of flames that ignite fuel particles were found to correlate with instabilities induced by the strong buoyancy of the flame zone itself. Discovery that ignition in wildfires is critically dependent on nonsteady flame convection governed by buoyant and inertial interaction advances both theory and the physical basis for practical modeling.
Wildland fires are distinguished from industrial and urban fires by the kinds and sizes of the fuels available. Forests, shrublands, and grasslands are characterized by small, discrete particles, such as leaves, pine needles, grasses, bark, twigs, and other wood particles, which are highly dissected compared with pools of liquid fuel spills or the large, continuous, solid surfaces of furniture and buildings.
All fires spread by transferring heat from the burning zone to new fuels 1 , but the complex chemical nature of natural fuels 2 , the fineness of the fuel particles in wildland fires and their separation by air spaces, create fire-spread conditions much different from those in urban fires. In fact, decades of research into ignition processes have not established an accepted theory explaining the ignition and spread of wildfires 3. Without a theory based on fundamental principles, the feedback processes of heat transfer and combustion that govern spread rates and the potential for extinction cannot be reliably modeled.
Thus, fire-spread modeling has been based on widely varying physical assumptions 4 and empirical relationships applied to steady-state conditions. Although still useful, these approaches are inadequate for predicting fire spread in a variety of fuel complexes; estimating fire effects on vegetation, soils, and the atmosphere; training firefighters to recognize imminent hazards; and expanding opportunities for vegetation management.
As wildfires increasingly impact human communities worldwide, climates continue to change, and more land is developed for human habitation and industry 5 , 6 , the need for a deeper understanding of wildland fire spread has become more urgent.
The study of physical processes associated with the spread of wildland fires began in the s with the recognition that fuel particles ignite after sufficient amounts of radiative and convective heat are transferred to them from a burning zone 7. Many models have been based on this understanding, but consensus has not been reached on the respective roles of radiation and convection on fire spread 4.
Radiation has been the most intensively studied and has often been assumed to govern spread 3 , but recent findings reveal that the heat flux from radiation is insufficient alone to support fire spread.
The explanation is twofold: First, radiation is heavily attenuated in porous fuel beds, where vegetation blocks some fraction of radiation from the burning zone to unignited fuels until the fire is very near 9. In fire-spread experiments using shallow beds of dry fuels, particle temperatures rose sharply only when the leading edge of the fire was within centimeters of the particles 10 , Wildland fuel beds with typically fine-sized fuel particles 16 exhibit high convection heat transfer 3 , 17 because heat transfer coefficients for free and forced convection are an inverse function of characteristic surface length, rising dramatically below 1 mm 3 , If radiation itself is insufficient to account for fire spread among small wildland fuel particles, convection must provide the explanation.Chartering unauthorized endorse any property customary business practice, that this position is held by arbitration practice.
The structure and intermittency of flames that ignite fuel particles were found to correlate with instabilities induced by the strong buoyancy of the flame zone itself. Business forecasting a managerial approach, Thomas E.
Malcolm X is one of the most important figures in the twentieth-century struggle for equality in America. Thirty measurements were taken of each charcoal sample.
Char was carefully scraped from the upper surface of the charcoals, so as to capture the same surface that had been analyzed for charcoal reflectance; two samples were collected from each flaming duration. Char forming fuels rapidly reach a peak burning flux and the maximum point of energy release from flaming, then their energy release rate decays over time Figures 2 , 10B.
When charcoal reflectance was measured at depth intervals throughout the char layer, the reflectance could be seen to decrease with depth through the char profile Figure 5.