Fire safety system in tunnels (FBG)

Tunnel is important part of highway, railway and public transport. Number of tunnels with difficult terrain, relatively closed infrastructure and large volume of traffic increases every year. In connection with that, there is strong demand for provision of safe functioning of transport system, including fire safety.


Features of monitoring systems - fire annunciators in tunnels:

  • Prompt timely response of the monitoring system on the occurrence of ignition as spread of fire along with the smoke occurs very quickly within 5-10 minutes.
  • Accurate identification of ignition sources location. Tunnel is relatively small and narrow space that quickly fills with smoke that spreading in the direction of the wind.
  • Monitoring system that provide ability to adjust alarm thresholds. Depending on the weather conditions, in particular the time of year, the alarm thresholds can change. 
  • Extremely polluted environmental conditions, including high humidity, would not affect operability of monitoring system.
  • System is easy to maintain.

Fiber-optic systems for fire safety of tunnels, based on FBG, possess all above features.   

Comparison of fire safety monitoring systems 



Linear temperature sensors

Light sensor

Smoke detector



Flame detector

Smoke detector

Speed and accuracy of ignition recognition

Early fire notification, quick response, location of ignition center ± 1 m

Early fire notification, quick response, more accurate ignition center detection

Delayed detection time, accuracy of 50 m detection

Detection of fire by large amount of smoke, which does not allow to determine in timely manner center location of ignition

Environmental adaptability

Not depend on humidity, are neutral to effect of exhaust gases

Susceptible to smoke, dust, vulnerable to other light sources

Vulnerable to exhaust gases, dust

Installation and maintenance

Installation is simple, quick sensor sampling, easy to maintenance


Usually installed in the control room

Price comparison

Profitability in monitoring of long tunnels

Profitability in monitoring of short tunnels

Profitability in monitoring of very short tunnels

Inexpensive systems


 As such, it can be concluded that use of FBG systems for short tunnels (up to 0.5 km) is advisable.

Fire protection system in tunnels, which based on the FBG fiber-optic temperature measuring system, is unified fiber interrogation unit (FIU), integrated into general safety system of tunnel, with connected chain of OSCT optical temperature detectors (fire detectors) installed at facility. Such system is more accurate in recognition of ignition location