SAFETY/FIRE | TECHNICAL
SMOKE CONTROL IN ROAD TUNNELS
To minimise smoke propagation in tunnels, ventilation design has seen the
distributed extraction approach give way to local extraction systems for new tunnels. Ingo Riess, of Riess Ingenieur-GmbH, in Zurich, Switzerland, discusses the change, its effectiveness, but also the challenges that come in the complexity of the new approach
In the past 25 years, the standard for road tunnel ventilation has improved tremendously. The main design objective of tunnel ventilation shifted from in-tunnel air quality to smoke control for self-rescue. This development was accelerated by the disastrous fires in the Montblanc, Tauern, and Gotthard tunnels in 1999 and 2001. At the same time, computer models were developed
that allowed a better understanding of the dynamic behavior of tunnel ventilation systems. Before, tunnel ventilation design and operation were mostly based on steady state situations. Later, the dynamic behaviour was analysed. For system response it was distinguished between self-rescue and firefighting phases. In this article, we concentrate on smoke extraction,
on the ventilation concept for smoke control in long tunnels, for bi-directional traffic and for congested traffic.
HISTORY: FROM TRANSVERSE VENTILATION TO SMOKE CONTROL DAMPERS In 1927, the Holland Tunnel in New York was the first road tunnel utilising a fully transverse tunnel ventilation system.
As transverse ventilation, we consider a system
with distributed fresh-air injection and distributed exhaust. Before, tunnels had been ventilated naturally by longitudinal airflow. In the 1980s and early 90s, smoke extraction systems
were still designed as section-wise distributed extraction. This was the obvious choice as the ventilation design was driven primarily by the requirements for in- tunnel air quality.1
This was the case especially for long
bi-directional tunnels, such as the Montblanc, Tauern, and Gotthard tunnels. Extraction ducts were typically connected to the tunnel with small, evenly spaced open vents.2
In
response to a tunnel fire, the fresh air supply was reduced while the exhaust in the fire section was maximised. In some tunnels, fresh-air supply fans were reversed to extract smoke through fresh air vents. But the tunnel fires in 1999 and 2001 indicated the limited capabilities of this concept. In the Montblanc and Gotthard fires, there was a
significant barometric pressure between the tunnel portals, causing high flow velocity in the tunnel and rapid smoke propagation. But even without meteorological pressure, the effectiveness of distributed extraction is limited.
Right, figure 1: Smoke damper FAT in 2003
ILLUSTRATIONS AND IMAGES COURTESY OF INGO RIESS
August 2023 | 11
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