Modeling of the Drift and Accumulation of Tsunami-Driven Combustible Objects: Towards Tsunami-Induced Fire Spread Simulation.

Fires that break out in tsunami inundation areas are collectively referred to as 'tsunami-induced fires' in contrast with 'seismic-induced fires' which have been conventionally a serious concern in Japan. Scenario of this new fire is basically as follows: (1) combustible objects such as houses are washed away by a tsunami, (2) combustible objects accumulate in tsunami inundation area as debris, (3) debris are ignited by some kind of cause, and (4) fires spread to adjacent debris resulting in conflagration in tsunami inundation area. We have been modeling tsunami-driven combustible objects as the first step towards development of tsunami-induced fire spread simulation. This modeling aims to know how combustible objects accumulate in tsunami inundation area to be the input data to fire models for ignition and fire spread. The proposed model is the extension of the existing model for driftwood by incorporating the debris release model and the effect of debris's collision with surviving buildings. This model collaborates with the existing numerical simulation of tsunamis and is able to predict the drift and accumulation behavior of individual debris by solving the equation of horizontal translational motion. In this paper, we conducted debris diffusion simulation for Yamada, Iwate prefecture, Japan for model's validation, where 16 ha of area were affected by tsunami-induced fire spread after the 2011 Great East Japan Earthquake Tsunami. The total number of debris tracked in the simulation was 1,850,560. A constant of proportionality, which determines the severity of force acting on drifting debris due to the collision with onshore surviving buildings, was identified by trial and error to maximize the eventual amount of accumulating debris within the fire-damaged zone. As a result, this maximum amount was predicted to be 4654 tons in the case that the constant is 0.1. Two thirds of the released debris, about 12,000 tons, accumulated onshore at the end of computation, and most of the fire-damaged zone was covered by these debris. [ABSTRACT FROM AUTHOR]