The objective of the tunnel ventilation system is to control and/or to extract smoke and heated gases and provide a non-contaminated environment for egress of tunnel users. Another objective is to support firefighting and rescue operations.
In both cases, the primary goal is to control smoke and hot gases as the result of fire during any eventuality. The amount of smoke and heat generated depends on the fire size.
It is often assumed that the smoke generation and heat generation rates are proportional to the fire size. In general, the larger the fire size the more combustion products the fire produces and hence, more air is required to control smoke and hot gases. However, this ratio is not linear.
There are different type of ventilation system used in tunnels most commonly used ventilation is longitudinal ventilation system using the JET Fans in smaller tunnels.
The type of ventilation is also based on certain parameters like fire volume, traffic direction and density, gradient, over burden of the tunnel, length of the tunnel etc.. The solution should be based on project based to optimize the usage of ventilation, power, feasibility etc ..