Post-earthquake Fire Spread Between Buildings Estimating And Costing Extent In Wellington

Abstract

Fires after earthquakes sometimes develop into conflagrations resulting in widespread losses of life and property. A geographic information system (GIS) model linked to property and valuation data is shown to be an appropriate tool for estimating urban fire losses. One approach uses a static buffering technique to define potential burnout zones that are sampled randomly to give estimates of losses. The other uses a dynamic cellular automaton technique for determining both the rate and extent of fire-spread in response to a wide range of factors including wind, radiation, sparking, branding, building separations and building claddings. The dynamic approach uses a set of 'rules' based on fire physics modified by historical data. The model runs in real time for single ignitions. The static method is used to estimate losses assuming a 12m separation will prevent fire spread All buildings are assumed combustible (upper bound case). The dynamic model assuming fire can not spread to buildings with non-combustible claddings and areas of vegetation are not flammable (lower bound case).

Development and validation of a physics-based urban fire spread model

“…Accuracy of the model was supplemented by adjusting the involved empirical constants so that the simulated fire spread rate agrees well with that of the past incidents. Basic concepts of the models developed later on are similar to those of the Hamada model, in which they describe the macroscopic behaviors of fire spread with empirical relations [4,[6][7][8][9][10][11][12]. The advantage of such an approach of modeling is that it can simulate the rate of fire spread with a fairly simple procedure.…”

Probabilistic Modeling of Post-Earthquake Fire in Wellington, New Zealand

“…For modeling the losses from spreading fires we used a static “burn-zone” model that was developed specifically for Wellington (Cousins et al 2002, Thomas et al 2002). The model relied on the specification of a “critical separation,” which was the maximum distance that a fire could jump from one building to another under a specified set of conditions.…”

“…Wind is very important because strong winds can carry sparks and burning brands over considerable distances. The relationship between wind speed and critical separation (Figure 6) has been derived from a combination of fire physics and historical data (Cousins et al 2002, Thomas et al 2002). Under calm conditions, when radiation was the only fire-spread mechanism available, the greatest gap that a fire was allowed to jump was about 12 m. For moderate-to-fresh breeze conditions (20 to 30 km/h) the dominant spread mechanism was piloted ignition, which involved radiant preheating followed by contact with wind-blown sparks.…”

“…New Zealand is a highly seismic country experiencing, on average, one magnitude 7 or greater earthquake every eight years or so (Figure 1). Its history of post-earthquake fire mirrors that seen worldwide, with only one earthquake, the magnitude 7.8 Hawke's Bay earthquake of 1931, causing serious fire losses (Table 1) (Thomas et al 2002). More than 250 people were killed in that earthquake and three spreading fires destroyed nearly the entire business district of the city of Napier, making it New Zealand's worst historical earthquake disaster (Conly 1980, Dowrick 1998).…”

Risk and Behavior of Fire Spread in A Densely-built Urban Area

“…Several approaches have been taken so far, generally by using empirical-or GIS based-fire spread models [2][3][4][5][6][7][8][9][10]. In these models, rates of fire spread are usually formulated as functions of macroscopic parameters of the relevant city area, such as wind speed, building scale, building-to-building separation, construction types, etc..…”