Tunnel ventilation facilities, for road or rail tunnels, face the challenge of the design requirements imposed on them. Among them is the Fire Heat Release Rate (FHRR). Many think that the larger the FHRR, the safer the system, but the fact is that if FHRR is too large, the airflows required for a ventilation system to control the smoke become too large, the facility requires a lot of space, and the cost may escalate to the point that the constructability of the ventilation plant may be too costly to build.

The airflow rate through the tunnel ventilation facility and fan duty points are key parameters. The airflow through the tunnel ventilation facility is a function of the tunnel configuration constraints; while the duty point is a function of the number of fans, individual fan airflow, equipment room layout, and airflow path. The airflow rates are determined through computer modeling taking into account numerous branches and tunnel network losses. The duty point is usually determined by hand calculations (for simple systems), but sometimes, it becomes very difficult that we need to carry out computer modeling. This paper will illustrate that there is a non-linear correlation between the magnitude of change in the FHRR, and the sizing of the tunnel ventilation facility. Ultimately, there is a change, but through computer simulations, these changes will need to be assessed.