FIRE FIGHTERS have this week praised the fire safety engineering which prevented a fatal tunnel fire in the Channel Tunnel Rail Link (CTRL) from escalating into a major incident.
Two construction workers were killed in a blaze on 16 August which is believed to have broken out in a diesel locomotive drawing a construction train south through the 2.5km long, 8.15m external diameter eastern bore of CTRL's Thames crossing.
Emergency services were called to the scene after a CTRL manager noticed smoke pouring out of the southern portal. Firefi ghters were able to extinguish the blaze with dry powder extinguishers before any major damage had been caused to the tunnel lining.
But fire safety engineers said this week that the fire would have been far worse had it not been for the tunnel's emergency ventilation system.
'Our job was made very much easier by the efficiency of the Saccardo ventilators, ' said Kent Fire & Rescue divisional officer and Thames Crossing liaison officer Graham Gash.
Each of the four portals has a Saccardo ventilator. This uses a nozzle system producing high velocity air to draw in large volumes of air from the portal in an emergency (see diagram).
'During this fire the ventilator at the Essex portal of the bore where the loco was burning was actuated to cool and dilute the fl ames and blow them forward, away from the locomotive, ' explained CTRL project manager Halcrow fire safety engineering director Dr Fathi Tarada.
'At the same time the ventilators at both ends of the other bore were switched on. These pressurised the tunnel and cross passages to keep it clear of smoke, ' Tarada added.
Gash said there was 'a very tenable working atmosphere close to the site of the fire', and no ignition of the contents of the flatbed wagons behind.
The train was carrying large drums of cable and was returning from joint venture track contractor ACT's workface when the blaze broke out.
Gash said that if the wagons had caught fire the resulting blaze would have been much hotter and could have threatened the integrity of the tunnel's precast concrete segments.
Lessons of the 1996 Channel Tunnel fire meant these were cast from C50/60 concrete with polypropylene fibres included to minimise the risk of explosive spalling under fire loads.
'In fact we saw no structural damage to the tunnel lining at all', Gash said. 'I really can't praise the ventilation system enough, its performance made all the difference.'