A Numerical Study for Assessing the Risk Reduction Using an Emergency Vehicle Equipped with a Micronized Water System for Contrasting the Fire Growth Phase in Road Tunnels

Ciro Caliendo,Isidoro Russo,Gianluca Genovese

doi:10.3390/app11115248

Abstract

We performed Computational Fluid Dynamics (CFD) modeling, and simulated a people evacuation process from a tunnel in the event of a fire, for evaluating the potentialities of using, as a temporary safety measure, an emergency vehicle equipped with a micronized water system for contrasting the fire growth phase. The structure investigated is a one-way road tunnel with only natural ventilation, and with a length less than 1000 m. The tunnel is assumed at present to be affected by refurbishment works for making it comply with the minimum safety requirements of the European Directive 2004/54/EC. In particular, it is considered that it has not yet been provided with hydrants, and with the sidewalks and the emergency exit which are still under construction. This means that users are forced to use the road carriageway for escaping from the tunnel if a fire occurs. The CFD findings have shown that the use of the micronized water system might lead to a significant improvement in the environmental conditions along the escape route since the tenability limits of temperature, radiant heat flux, CO and CO2 concentration were found to be better satisfied. Additionally, the visibility distance was shown to increase, even though it was found to be higher than the acceptable threshold value only in a few cases. However, the quantitative risk analysis based on a probabilistic approach, which was combined with a method currently used in Europe for assessing the risk due to the transit of only dangerous goods, shows that the final cumulative F-N curves related to the micronized water system always lie below those without the mentioned system, and in addition, they are always contained within the limits of the ALARP region. It is to be stressed that our paper might represent a reference in showing the effectiveness of the micronized water system as a temporary safety measure. However, it is desirable that the Tunnel Management Agencies accelerate the refurbishment works for making road tunnels definitively safer for users in a short period of time.

Highlights

After catastrophic events due to fires occurred in some road tunnels in Europe (i.e., Mont Blanc tunnel, Tauern tunnel, and Saint Gotthard tunnel), the European Parliament and Council adopted the Directive 2004/54/EC [1]
The number of potential users exposed at risk of fatalities and/or injuries in the event of a fire in the investigated tunnel was evaluated by means of the Fractional Effective Dose (FED) concept, for which an escaping user is considered to be incapacitated and unable to reach a safe place when the FED due to the exposure of toxic gas concentration (FEDtoxic gases) and/or due to the heat and radiant heat flux (FEDheat) is more than 1
This research was mainly motivated by the need to perform a computational fluid dynamics modeling for assessing the effectiveness of a temporary safety measure, which is based on the use of an emergency vehicle equipped with a micronized water system, for contrasting the fire growth before the arrival of the fire brigade in road tunnels that are still involved in refurbishment works necessary for adapting these structures to the provisions of the European Directive [1]

Summary

Introduction

After catastrophic events due to fires occurred in some road tunnels in Europe (i.e., Mont Blanc tunnel, Tauern tunnel, and Saint Gotthard tunnel), the European Parliament and Council adopted the Directive 2004/54/EC [1] This Directive introduced the minimum safety requirements, for tunnels belonging to the Trans-European Road Network with lengths of over 500 m, with the purpose of ensuring an appropriate safety level to tunnel users. Due to the very high density of tunnels in Italy, most of these structures still present works in progress For this reason, the Italian Tunnels Permanent Commission has recently imposed on the Tunnel Management Agencies (TMAs) the implementation of certain temporary safety measures for tunnels that have not yet achieved the minimum safety requirements. The intervention time of the rescue team for this purpose, for example in the case of a tunnel open to traffic with a length < 1000 m and without any emergency exit (except the entrance and exit portals of vehicular traffic), is required to be less than 10 min from the fire’s start

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Conclusion