Modelling the Effects of Boundary Walls on the Fire Dynamics of Informal Settlement Dwellings

Abstract

Characterising the risk of the fire spread in informal settlements relies on the ability to understand compartment fires with boundary conditions that are significantly different to normal residential compartments. Informal settlement dwellings frequently have thermally thin and leaky boundaries. Due to the unique design of these compartments, detailed experimental studies were conducted to understand their fire dynamics. This paper presents the ability of FDS to model these under-ventilated steel sheeted fire tests. Four compartment fire tests were modelled with different wall boundary conditions, namely sealed walls (no leakage), non-sealed walls (leaky), leaky walls with cardboard lining, and highly insulated walls; with wood cribs as fuel and ISO-9705 room dimensions. FDS managed to capture the main fire dynamics and trends both qualitatively and quantitatively. However, using a cell size of 6 cm, the ability of FDS to accurately model the combustion at locations with high turbulent flows (using the infinitely fast chemistry mixing controlled combustion model), and the effect of leakage, was relatively poor and both factors should be further studied with finer LES filter width. Using the validated FDS models, new flashover criteria for thermally thin compartments were defined as a combination of critical hot gas layer and wall temperatures. Additionally, a parametric study was conducted to propose an empirical correlation to estimate the onset Heat Release Rate required for flashover, as current knowledge fails to account properly for large scale compartments with thermally thin boundaries. The empirical correlation is demonstrated to have an accuracy of ≈ ± 10% compared with the FDS models.

Experimental and Numerical Study for the Effect of Horizontal Openings on the External Plume and Potential Fire Spread in Informal Settlements

“…The analysers measured the O 2 , CO 2 , and CO gas concentrations, in addition to the hydrocarbon products in parts per million (ppm). In alignment with what was found by Beshir et al [15], the combustion efficiency was captured well by the FDS at locations with low turbulence. The steady state gas concentrations of oxygen and carbon dioxide were found to be very similar for both experimental and numerical work for both the CL and S_0.04 cases with a variation of about ±5%.…”

“…Since 2017, there have been many experimental and numerical studies to fill the gap of knowledge for these unique compartments and fire spread techniques. In summary, these studies have included (1) bench scale material tests (Wang et al [8]); (2) small scale experiments determining heat transfer and the heat release rate needed for flashover in thermally thin and thick boundaries (Beshir et al [9]); (3) large scale outdoor compartment fire experiments determining the difference between timber and steel clad ISD fire behaviour (Cicione et al [10]), fire spread (Cicione et al [11]), and critical separation distance; (4) full scale laboratory experiments to understand the fire dynamics and the effect of different boundaries (Wang et al [12]) and test current theories for temperature, flame shape, and flashover conditions (Wang et al [13]); (5) modelling the results of these experiments to determine controlled experiments required to validate the Fire Dynamics Simulator (FDS) ISD models [14] and the utility of FDS in capturing fire dynamics in ISDs (Beshir [9,15]); (6) wind tunnel simulations to understand the effects of the wind on the fire dynamics (Centeno et al [16]); and (7) fire risk mapping using remote sensing and GIS techniques (Stevens et al [17]) for fire spread modelling (Cicione et al [18]) and determining critical separation distance (Wang et al [19]).…”

Laboratory experiment of fire spread between two informal settlement dwellings

“…In this work [38], it was proved that in thermally thin bounded compartments the boundaries (walls) get heated up relatively quickly and act as a radiator to the cold items within the compartment preflashover. The importance of the walls' emissivity on the HRR needed for flashover was highlighted.…”

“…Thus, to calculate the critical HRR for thin metal dwelling, a new equation, similar in format to Eq. ( 10) and generated based on the authors' research [38,39], is proposed:…”

Numerical Study on the Effect of Atmospheric Wind on the Fire Severity in Informal Settlements with Different Dwellings’ Wall Thermal Characteristics

“…Based on that, a semiempirical correlation was developed to predict the Heat Release Rate (HRR) required for reaching flashover ( _ q fo ) in thermally-thin compartments, based on the emissivity of the walls, the total walls area and the ventilation factor for smallscale ultra-fast fires. Posteriorly it was observed that this correlation does not hold for large scale compartments with medium/fast fires (wood cribs) [14].…”