Responding to multiple simultaneous fires during large earthquakes remains a serious issue. To reduce seismic damage, fires that are expected to spread widely must first be extinguished using a sufficient water source. However, debris from collapsed buildings may block narrow streets, making it difficult for firefighters to arrive smoothly at fire sites. In addition, a lack of water due to water outages at some hydrants may prevent prompt firefighting. In previous studies, we constructed and integrated simulation models which described urban damage (such as the spread of fires and street blockages) and firefighters' activities. The simulation results showed fires with a high risk of spreading could be identified, and if firefighters were immediately dispatched to the sites of these high-risk fires, the number of burned-out buildings was likely to be greatly reduced. On the other hand, we assumed that firefighters would use water sources other than hydrants since some hydrants might not be available due to water outages.
In this paper, to consider the availability of hydrants for firefighting after a large earthquake, we first constructed a water outage simulation model on the network of water service pipes, which was estimated based on the street networks. This technique is effective in cases where a large number of water pipes exist under the streets, as found in the Tokyo Metropolitan Area. Second, we estimated the destroyed pipes based on the characteristics of the pipes and ground surface, where the pipes are located, and earthquake response. Third, we determined the hydrants that would be out of water using a reachability analysis. The water outage simulation results, in the case that a northern Tokyo Bay earthquake were to occur, showed that the water failure rate was likely to be high in the zone far from water purifying plants and the zone where liquefaction damage might occur. It is one of the efforts of this paper to develop a simulation system of water failure on the water service pipes network.
Next, we integrated this water outage simulation model into the urban damage simulation model and firefighters' activity model. Finally, we analyzed the effects on the prevention of fire spreading of using hydrants. In the case that the water supply was not cut off to any of the hydrants, the number of burned-out buildings could be reduced by a maximum of about 400 from in the case without hydrants. The number of burned-out buildings was estimated by the fire-spread simulation results from the fires that firefighters failed to extinguish because of late arrival times. When some hydrants were not available due to water outage, the number of burned-out buildings was little increased in some jurisdiction of firefighters. In contrast, if water outage rate is not high, the number of burned-out buildings could be reduced by a maximum of more than 100.
When firefighters understood that all hydrants had water outages using the widespread water pressure meter system—which is accessed using the Personal Handy-phone System (PHS) available after large earthquakes—the number of burned-out buildings was reduced in almost every jurisdiction for firefighters. Moreover, in some jurisdictions with low water outage rates, the number of burned-out buildings was likely to be reduced by about 200. In addition, there are about 20, 000 buildings which exist farther than the length of 22 hoses from water sources other than hydrants, and in the length from hydrants by airline distance. These buildings could not be reached by firefighters without hydrants. Thus, it is necessary to consider using hydrants when firefighters can understand the status of hydrants, particularly in areas with few fire cisterns.
