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Evacuation alarms in tunnels

Tunnel Alarm is a hot item nowadays. After the inferno in the Gotthardttunnel in Switzerland and in the Karawankentunnel in Austria we are yet again a little more aware of the fact that the effects of a disaster in a tunnel are quadratic. Within Europe, the requirements regarding tunnel security are properly tightened lately.

Evacuation Alarm is incredibly important in this application.

You can actually segment the tunnel route and thus you have projected zones. Zonewise broadcasting is of vital importance in case of emergencies. With the support of the CCTV system you can broadcast very focused to a location.

Strangely, there is little regulated in standards in tunnel evacuation alarm. In the German-speaking areas there are, however, special requirements applied to the speakers, and TMCDAS can also supply these certified speakers.

“In a tunnel there are quite a few external factors to be taken into account when projecting such an installation”

Environmental Noise
Due to the large amount of fans in a tunnel, there is a high ambient noise level of about 100 dB. The speakers should produce at least 10 dB higher audio, or preferably even slightly higher. If there is traffic, this is even a little higher. The speakers in tunnels must therefore deliver at least 120 dB power. This is a pretty high value and you will see that there are only a few suppliers of these speakers.

Speech intelligibility
The speech intelligibility in a tunnel will be abominable by all reflections. It is therefore important to apply speakers with corrected radiation characteristics. If you get an STi of 0.6, that is good. An advice is to project per lane at a distance of 50 meters a speaker. A STi close to 0.6 is then reasonable to realize. In practice will show that a STi of 0.5 is the maximum possible.

Implementation of a central
Because of the large amounts of high-power speakers, there are many amplifiers required. If the evacuation central is set up somewhere in an equipment room, it will usually result in long lengths of cabling. Cable losses will certainly play a role.

There should be made choices in wiring and / or master-slave configuration.

A thorough projection from both audio perspective and electrical background is important.

Redundancy of amplifiers
At tunnel signaling is a high degree of redundancy of the systems usual. We will always advice the customer to use a redundant amplifier per group of speakers, which are placed at a hectometer location.

”So at a location in the tunnel there is a full-redundant amplifier situated with ditto power supply and emergency power supply”

Obviously, the speakers are equipped with an approved isolator. Furthermore, the data transmission path of the amplifier, so the link on the central, needs to come from two separate fire compartments; the wiring is performed here twice. This is a reasonably high degree of fail-safe, but for example, in the world of Marin Solutions fairly common.

Certification
It has already been mentioned, but in the application of tunnel evacuation alarm it is not regulated. All the recommendations earlier, are recommendations made based on knowledge of audio and electrical engineering. Many standards and guidelines are available, and it is possible to formulate a good directive or program of requirement on short term.

A good starting point would be formulating the basics. If started with the principles of the EN54-16, we are already a long way. In addition, we need to impose conditions regarding to the electronic implementation.

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