Flame Spread along a Thin Combustible Solid with Randomly Distributed Square Pores of Two Different Sizes

The objective of our study is to predict the flame spread route by the quantity of combustible materials and their placement. In this paper, we examine non-uniform flame spread in open air along a thin combustible solid with randomly distributed square pores of two different sizes (8 x 8 and 4 x 4 mm respectively). Experimental results show that the flame-spread probability falls with increasing porosity. Despite uniform porosity, the flame-spread probability differs with the rate of large square pores to small square pores. For a combustible area larger than a noncombustible area, the flame-spread probability reaches the local minimum value with a change in R8 (ratio of 8 mm pores) under the same porosity condition. Conversely, for a combustible area smaller than a noncombustible area, the flame-spread probability reaches a local peak with changing R8 under the same porosity condition. In addition, we calculated the ratio of the unburned area (unburned area / total combustible area) by counting the unburned cells after the flame spread test, which might be useful to predict the fire hazard. We found that the ratio of unburned area grows with increasing porosity.

Multiple fires frequently occur in urban areas after a major earthquake.In fact, several fires broke out after the Great Hanshin Earthquake and Great East Japan Earthquake.Urban areas include combustible areas such as wooden structures and plants, as well as noncombustible areas, e.g.concrete buildings, roads, parks, and parking spaces.This means flames spread non-uniformly.In addition, it is difficult to predict the flame spread route because it also depends on the terrain and wind direction.Figure 1 shows photography of some urban area in Japan and a binary image, whereby the urban area is divided into combustible and noncombustible areas.As shown in Figure 1, combustible and noncombustible areas of various sizes are randomly distributed in an urban area.When a fire starts somewhere, one case involves the flame spreading and combustible materials burning out, and the other involves the flame self-extinguishing on the way.The threshold for burning out or self-extinguishing may be determined by the quantity of combustible materials and their placement.Establishing security by predicting the flame spread route is important to save human life in urban fires.
Many studies have been conducted focusing on flame spread along a uniform solid fuel load as a fundamental component of fire research, but few have examined non-uniform flame spread in mixed combustible / noncombustible materials.Recently, a few papers have been published concerning the application of percolation theory to non-uniform flame spread.Percolation theory reveals a probabilistic connection route among particles randomly arranged on a grid, which may or may not be useful in predicting flame spread.A few numerical simulations have also been conducted using a square grid model, however, discussing from an experimental perspective is rare.Therefore, in our previous paper, we conducted experiments concerning flame spread along a thin combustible solid with randomly distributed circle or square pores.We also discussed the relationship between porosity and flame-spread probability based on percolation theory.However, combustible and noncombustible areas vary in respective size in real urban districts, which affects the flame-spread probability and damage by fire, despite the ratios of combustible and noncombustible areas being the same.
In this paper, we studied the flame-spread probability along a thin combustible solid with randomly distributed square pores of various porosity and in two different sizes.In addition, we introduced the ratio of the unburned / combustible area, by counting unburned sample cells after the flame spread test, and discussing the hazard by www.ccsen fire.

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Since  The following conclusions can be summarized here: 1) The flame-spread probability decreases with increasing porosity.However, with changing R 8 at the same porosity, the flame-spread probability reaches the local minimum and maximum values at around 40 and 50% porosity respectively.At 60% porosity, some slits are formed and the flame-spread probability becomes nearly 0%.This tendency is similar to the threshold of percolation theory, meaning flame spread can be discussed in terms of percolation theory.
2) The average number of slits, N s , grows with increasing porosity ranging from 40 to 60%.However, N s differs with different R 8 at the same porosity.This difference is considered attributable to the presence or absence of a slit.For porosities of 40 and 45%, a slit is formed by distribution of small pores at R 8 of around 80%.For porosities of 50 and 55%, the flame spread route is formed by the distribution of combustible cells at R 8 of around 67%.For 60% porosity, almost two slits are formed for all R 8 .In fact, the flame-spread probability falls with increasing N s .
3) The ratio of unburned area to total combustible area grows with increasing porosity.This tendency is observed in all R 8 .However, under the same porosity condition, the R u differs with R 8 .The value of R u at 92% of R 8 peaks, and the value of R u at 57% of R 8 has a minimum value for all porosities.We suggest that the fire hazard in urban areas is most dangerous where the number of noncombustible small spaces is three times larger than that of large spaces.
4) The ratio of unburned area large increases around 60% porosity for all of R8.From a fire-safety perspective, it is advisable that the ratio of noncombustible area raise more than 60% relative to an urban area.Furthermore we should place the combustible materials in an urban area with spacing which fire cannot jump over. Fig Figur Figure 6 sh The image this figure flame pass meaning th In the cas combustib flame quic depends o which blo between p Figure 7 p noncombu despite un following (cases of 4 minimum noncombu maximum area (case Figure 10