SAFETY - The Westerschelde Tunnel: Approaching Limits - page 45

Fig. 4.7
One of the jet-fans in
the tunnel during the
fitting out phase
Safety during fire
The road surface is provided with dense-graded non-porous asphaltic con-
crete. Extremely open-graded asphaltic concrete was not an option for the
tunnel, because this increases the so-called evaporation surface and thus
increases the risk of explosion hazards if fuel or volatile substances end up
on the road surface.The diagonal slope of the road surface ensures that the
substances such as leaking fuel flow into the gutter at the side of the road as
fast as possible. From there it is discharged to one of the two explosion-safe
storage tanks under the tunnel.
The lining has a special heat-resistant cladding to protect the concrete lining
from heating up quickly and excessive temperatures that could cause
the concrete to spall. (See Chapter 5 'The protection of the Westerschelde
Tunnel against fire'.) This is how the collapse of the concrete structure is
prevented.
The pump installations present in the tunnel take care of the discharging of
rainwater, fire-fighting water and dispelled substances. In the access ramps,
main pump cellars have been constructed through which the rain water from
the open access ramps is discharged. Central pump cellars at the deepest
points of the tunnel catch the leak water and suchlike that has been driven in,
and discharge it to the main pump cellars.These drain the waste water (puri-
fied if necessary) into the open water nearby. 'Clean' water - not polluted by
the road traffic - is caught in separate water cellars and drained directly.
'Dirty' water is discharged via a purifier. Hazardous substances are tem-
porarily stored by the pump installations and are discharged in an alternative
manner, for example, to a special reservoir outside the tunnel, in a tanker or
a tank ship. The continual excess pressure ventilation in the pump cellars
prevents hazardous explosive gases from spreading out of these cellars.
Traffic controlling
The tunnel is provided with a traffic controlling system that controls and
guides the traffic in cases of a breakdown or a disaster. With this system it is
possible to:
- clear the left-hand driving lane within a matter of seconds;
- block a driving lane;