defr Glossar

The air quality in road tunnels is assessed by measuring the visibility and the CO concentration. Adherence to the prescribed limits is crucial in terms of driver safety: CO concentration because of the toxicity of this gas, visibility because of the accident danger. The carbon monoxide is produced by the combustion process in gasoline engines. Visibility is reduced by roadway dust, tire abrasion and by the soot spewed out by diesel engines. In years gone by, the CO concentration was usually critical, but the introduction of catalytic converters and the popularity of diesel engines have increased the importance of visibility. Because both measurements are used to control the speed of the ventilation fans, they are largely responsible for driver safety and also for keeping down the tunnel's running costs.

Another critical fact for the safety in road tunnels is the fire alarm/fire detection. To detect fires in tunnels at the earliest possibility contributes greatly to increase the chances of rescue for road users. Visibility determination


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