TUNNEL INSTALLATIONS - The Westerschelde Tunnel: Approaching Limits - page 231

When a burning (smoking) vehicle drives through the tunnel and thus passes
a visibility measuring device, the tunnel ventilation starts up automatically.
Smoke and other fumes are then discharged in the driving direction so that
traffic that has stopped in front of the fire does not experience any hindrance.
The tunnel ventilation is also activated automatically on detection of a slow
moving vehicle (speed is lower than 18 km per hour). The automatic acti-
vation commences 60 seconds after such 'stagnancy' detection. Anyway, this
activation value can be set between 0 and 300 seconds. In this interim period
the tunnel operator can interrupt the automatic activation if there is cause,
for example for a false alarm.This facility was installed in order to have con-
trol of the tunnel ventilation to safeguard the stranded traffic from smoke
and burning fumes if stagnancy is coupled with fire.
The jet-fans are booster fans and have an outer diameter of 1.70 metres, are
5.75 metres long, weigh 1,690 kg and have a power of approximately 85 kW.
The measured momentum is 2,400 N. Each tunnel tube is provided with 40
jet-fans. The jet-fans are suitable for use in a surrounding temperature of
250 °C for one hour.The mutual distance between the jet-fans was chosen as
such, that in case of fire only some of the jet-fans may fail as a result of the
temperatures being too high. If this causes the number of activated jet-fans
to be less than the minimum number required, it can be compensated by
activating jet-fans elsewhere in the tunnel tube.
In the design of the jet-fans, a lot of attention was paid to the noise output.
In connection with the clarity from the intercom system and the loudspeakers,
a noise volume of 107 dB is not exceeded; this is not the audible sound level
(in dB(A)), but an uncorrected calculation value.The audible sound in the tun-
nel tube has a level of approximately 96 dB(A), when all the jet-fans are on.
Excess pressure ventilation The cross connections (escape corridor)
between both tunnel tubes have been provided with an excess pressure
ventilation which is activated in cases of disaster. This excess pressure
ventilation blows air from the non-incident tube into the cross connection, so
that on opening the doors to the cross connection, no polluted air can enter
from the incident tube into the cross connection and the non-incident tube.
Fire extinguishing system
On the right-hand side of the road in the tunnel, there is an emergency post
placed at every 50 metres. Here, the stranded motorist will find a telephone
which connects him directly to the control room at the toll square. When an
emergency post is opened, this is automatically signalled in the control
room and a camera is (automatically) directed towards the emergency post.
Thus the operator sees immediately what is happening. In the emergency
post there is a foam-spraying extinguisher and a fire hose on a reel to be
able to extinguish starting fires. The professional fire brigade can connect
onto a fire hydrant in the emergency post which has a capacity of 2 m 3 per
minute. Here the emergency services personnel can connect their electrical
equipment into a socket.
With a mixture of water and a foam-forming agent, the foam-spraying
extinguisher has a capacity of 100 litres per minute and is suitable for the
extinguishing of oil and petrol fires. The fire hose has a length of 50 metres
so that, if an emergency post is unreachable because of a fire, it is still
possible to reach the fire. The fire-fighting water is automatically mixed
with a foam-forming agent for 25 minutes. Thereafter, extinguishing is still
possible with water only. However, by that time the fire brigade should
already be on location.
Water supply to the fire hydrant for the fire brigade occurs from the land
ends of the tunnel where, on both sides, there is a water reservoir of 120 m 3