Quantitative fire risk assessment of road tunnels through advanced consequence analysis

The thesis is focused on the fire risk in road tunnels and its numerical estimation through quantitative risk analysis (QRA) supported by fire and evacuation modeling. According to the in-force regulations concerning the Trans-European Road Network, the quantitative risk assessment is a mandatory step for existing tunnels that do not comply with the minimum structural safety requirements. When the risk does not reach the acceptability threshold, alternative configurations and mitigation strategies must be designed to reduce the residual risk under a suitable level, and again the QRA is useful to evaluate which choice is the best considering the actual risk reduction, in terms of Expected Value (EV) per year and cost-benefit ratio. The thesis is divided in three macro-sections, which are intended to provide, on the one hand, an overall view of the complexity of road tunnel systems and, on the other hand, the possibility of a precise estimation of the consequences of a fire event through advanced modeling, in line with the state of the art of the fire safety engineering (FSE). The first section introduces the reader to the topic of fire risk in road tunnels by the characterization of their main features (traffic, systems, etc.), the statistics and the regulations which impose the QRA. In the second section, a detailed description of background aspects of tunnel fire safety is conducted; in addition, parametric studies aimed to assess the capabilities of models in a tunnel context are illustrated. The third section details the proposed methodology for QRA, which is finally applied to two cases studies of unidirectional and bidirectional tunnels

Italian hybrid fire prevention code

Fire safety of residential buildings and activities subjected to fire inspection is a difficult task, especially when the safety targets have to be adopted in built buildings or in activities that are going to be modified into more complex ones. Generally, these circumstances show more constraints and it could be difficult to achieve an acceptable level of fire residual risk by prescriptive based fireregulations. Therefore, the Italian National Fire Rescue and Service in charge for fire safety, in August 2015 issued a new Fire Prevention Code whose design methodology is more oriented to fire performance based design rather than prescriptive fire codes. The flexibility of this new fire design methodology offers a very complex tool to experts in order to design fire safety measures and strategies of buildings and activities subjected to fire inspection. The present paper aims tohighlig hts the contents and the fire safety strategy design methodology of the new Italian Fire Prevention Code

Influence of panic on human behaviour during emergency egress for tunnel fires

Tunnel fires represent a complex multidisciplinary problem of great importance for the Safety Engineering, where different aspects converge and add difficulties in studying and modeling the phenomenon. The confined geometry, traffic conditions and different, sometimes inap-propriate, safety measures are combined with the unavoidable presence of humans inside vehicles, making tunnel systems highly dangerous and risky: an extreme action like a fire or an explosion can cause severe effects depending on the fire development and the occupant characteristics, both physical and cognitive. In such environment, panic often drives people actions: the main negative consequence is the increase of the evacuation time, called RSET (Required Safety Evacuation Time). As the evacuation time grows, the exposure time at high temperatures and smoke increases and so the possibility for people of getting intoxicated. This paper is thought as the prosecution of other two papers: “Risk analysis for severe traffic accidents in road tunnels” (Di Santo et al., Proceeding IF CRASC’ 15) and “Computational fluid dynamics simulations for the assessment of a road tunnel fire safety” (Baroncelli et al., Proceeding IF CRASC’ 15) in which the concepts of hazard and risk for tunnels are widely described. The aim of this paper is to highlight the importance of considering human behaviour for the Fire Safety Engineering and the possibility of its modeling with numerical codes as FDS+Evac, giving as example the study of different egress scenarios for a 3 km – long – tunnel placed in the Catania – Syracuse Highway

Design of a Pressurized Smokeproof Enclosure: CFD Analysis and Experimental Tests

Pressure differential systems have the purpose of maintaining tenable conditions in protected spaces for different types of building safe places, like escape routes, firefighting access routes, lobbies, stairwells and refuge areas. The aim of pressure differential systems is to establish airflow paths from protected spaces at high pressure to spaces at lower or ambient pressure, preventing the spread of toxic gas released during a fire. This strategy ought to be supported by a detailed design of the necessary air supply, considering also the cycle of opening and closing doors during the egress phase. The paper deals with the design of a simple pressure differential system intended to be used in a building as a pressurized smokeproof enclosure. Specifically, experimental tests and numerical modelling are conducted with the objective of characterizing the pressure evolution in a small compartment under different conditions and through a cycle of door opening. Experimental tests are conducted in a simple 3-m side cubic enclosure with two doors and no vent openings. While a centrifugal fan blows constant airflow inside the structure, the pressure trend in time is recorded during steady state and transient conditions; additionally, the velocity of the airflow across the doors has been measured by means of an anemometer. Numerical CFD (computational fluid dynamics) simulations are carried out to reproduce the same smokeproof enclosure configuration (both geometrical and boundary conditions) using the fire dynamics simulator (FDS). Furthermore, specific attention is paid to the modelling of the leakage across the doors, directly inserted in the model through a localized HVAC (heating and venting air conditioning) advanced leakage function. Comparisons between experimental tests and numerical simulations are provided. Once the model was correctly calibrated, other geometrical and mechanical configurations have been studied, looking for convenient and efficient positions of the fan in order to fulfill the requirements of the pressure differential, airflow velocity and door handle force. The paper highlights some fundamental aspects on the pressurization and depressurization during steady state and transient phases, trying to identify if there are airflow profiles typical of some geometrical configurations

Fire Detection System Reliability Analysis: An Operational Data-Based Framework

This paper describes a framework developed at CERN, conducting reliability analysis of Safety-Critical Systems (Fire detection and Alarms) based on operational data. It applies Fault-Tree Analysis on maintenance-related data, categorized based on the component on failure. This framework, a tool implemented in Python, accounts for Fire Detection components installed in tunnels and surface buildings (control panels, detectors, etc) and safety functions triggered upon detection (evacuation, alarms to the CERN Fire Brigade, compartmentalization, electrical isolation, etc). The usefulness of the results of this type of analysis is twofold. Firstly, the results are a supporting tool for estimating the yearly availability of Fire Detection Systems in critical facilities, crucial in Capital and Operational Expenditure identification. Additionally, this approach refines the frequency analysis as part of quantitative fire risk assessments performed in the context of the FIRIA (Fire-Induced Radiological Integrated Assessment) Project, launched by CERN in 2018 and aiming at assessing the risk of fire events in experimental facilities with potential radiologic consequences to the public