# Effects of the Ventilation System by Using Jet Fans during a Fire in Road Tunnels
## 1 Introduction  
Road tunnels pose the greatest danger for fires [1; 2]. Due to the confined spaces, the effects of a road tunnel fire that starts naturally or as a result of a car accident can be disastrous [3; 4; 5]. According to estimates, there are about 25 tunnel fires per 100 million kilometers of vehicle travel; 10 of these involve heavy vehicles carrying no risky goods and 2 involve heavy vehicles carrying dangerous goods. [PERSON] et al. [6] state that smoke inhalation causes 85% of fatalities in underground fires. Furthermore, in China, car technical issues account for more than half of tunnel fire accidents (TFAs). To accurately define the technological systems for tunnel safety and to evaluate the safety conditions of a road tunnel, this type of risk must always be taken into account. The factors that make the tunnel a place with particular needs from the point of view of fire precautions are many [7]:  
* The confined environment, with the possible achievement of high temperatures and the production of toxic gases that can involve users;
* The presence of a high amount of combustible material inside the tunnel, in particular with regard to the fuel in vehicle tanks and the high calorific value of some materials inside heavy vehicles;
* The influence of natural or mechanical ventilation on the evolution of fire and on the propagation of temperatures and toxic gases;
* The difficulty of accessing from the outside in order to intervene with the aim of containing or extinguishing the fire, or to reach and rescue the people inside the tunnel. Analysis of previous tunnel incidents has shown that fires start in the vehicle's chassis, which contains the fuel and ignition sources. The oxygenation brought on by natural or artificial ventilation then allows the fire to spread to other nearby materials. Because of the tunnel's closed structure (heat and fumes are kept contained) the temperature raises, the air quality degrades, and visibility reduces, rendering the environment uninhabitable even far from the point where the fire began. The three tragedies that occurred in Europe at the turn of the century--the Tauern Tunnel (Austria), which claimed twelve lives, the St. Gotthard Tunnel (Switzerland), which claimed eleven, and the Mont Blanc Tunnel (France-Italy), which claimed thirty-nine lives--had a profound emotional impact on the public [8]. As a result, the discussion on road tunnel safety was expanded to include administrations, managers, designers, technical specialists, and users. They also asked for regulatory responses from the European Union. More precisely, there was a deficiency in mechanical ventilation during the emergency stage. Additionally, there were no communications made to travelers during the emergency phase, and the fire's fumes rendered the environment uninhabitable even far from the site of ignition. In all these cases, it was necessary to wait for the natural extinction of the fire, for several hours after it was started, with serious damage to the tunnel structures. To effectively manage a fire, it is necessary to know its dynamics and to understand the effects in terms of smoke production (toxic combustion gases) and temperature increase. Catastrophic fires in road tunnels have highlighted the need to study the dynamics of fires in detail: the rate of heat release over time (_HRR_--heat release rate) and the quantity and speed of smoke inside the tunnel. The starting point for these studies was the research carried out in the past on compartmentalized fires (i.e., those fires in an enclosed environment, such as a building). Over time, some interesting experimental studies have been carried out to analyze these phenomena, in particular the spread of fires between nearby vehicles. Much knowledge derives from full-scale on-site tests on fires (Eureka 499 Firetun 1991-1992 project, European project developed in Norway; 1993-1995 Memorial Tunnel project in the USA) and back-analysis of large fires in tunnels and underground mines.