Summit Tunnel fire

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The Summit Tunnel fire occurred on a dangerous goods train passing through the Summit Tunnel on the Lancashire/Yorkshire border, between Littleborough and Todmorden, England.

The tunnel was built in the late 1830s and was provided with blast relief shafts at intervals of (approximately) 200 m to vent steam from the locomotives that passed through it.

The fire occurred at 5.50 a.m. on December 20, 1984 when a goods train carrying more than a million litres (835 tonnes) of four-star petrol in 13 tankers entered the tunnel on the Yorkshire side. One-third of the way through the tunnel, a defective axle bearing derailed the fourth tanker, which promptly knocked those behind it off the track. Only the locomotive and the first three tankers remained on the rails. One of the derailed tankers fell on its side and began to leak petrol into the tunnel. Vapour from the leaking petrol was probably ignited by a hot axle box.

The three train crew could see fire spreading through the ballast beneath the other track in the tunnel, so they ran the remaining mile to the south portal (where they knew there was a direct telephone connection to the signaller) to raise the alarm.

Crews from Greater Manchester and West Yorkshire fire brigades quickly attended the scene. Co-ordination between the brigades appears to have worked well, perhaps because they had both participated in an emergency exercise in the tunnel a month before.

Figure 1: looking south along the upline track, showing petrol tankers 11 and 12.

The train crew were persuaded to return to the train, where they uncoupled the three tankers still on the rails and used the locomotive to drive them out. Greater Manchester fire brigade then loaded firefighting equipment onto track trolleys and sent a crew with breathing apparatus in to begin their firefighting operation at the south end of the train. They also lowered hoselines down one of the ventilation shafts to provide a water supply. At the same time, crews from West Yorkshire fire brigade entered the tunnel and began fighting fires in the ballast at the north end of the train, at the location shown in Figure 1.

However, at 9.40 a.m. the pressure in one of the heated tankers rose high enough to open its pressure relief valves. The vented vapour caught fire and blew flames onto the tunnel wall. The wall deflected the flames both ways along the tunnel, the bricks in the tunnel wall began to spall and melt in the flames and the BA crews from both brigades decided to evacuate. They managed to leave just before the first explosion rocked the tunnel.

Left to itself, the fire burned as hot as it could. As the walls warmed up and the air temperature in the tunnel rose, all ten tankers discharged petrol vapour from their pressure relief valves. Two tankers melted (at approximately 1530 °C) and discharged their remaining loads as floods.

The fuel supply to the fire was so rich that some of the combustibles were unable to find oxygen inside the tunnel to burn with: they were instead ejected from shafts 8 and 9 as superheated, fuel-rich gases that burst into flame the moment they encountered oxygen in the air outside the tunnel. At the height of the fire, pillars of flame rose from the shaft outlets on the hillside above (Figures 2 and 3: bear in mind that the shafts are 3 metres (10 feet) diameter and that the flames are about 45 m (145 feet) high).

Figure 2: Pillars of flame from vent shafts 8 and 9 at the height of the fire.

Figure 3: Close-up of vent shaft 8; the tree and dirt road to the right of the shaft give a sense of scale.

The gases are estimated to have flowed up these shafts at 50 m/s (110 mph). Air at this speed is capable of blowing around fairly heavy items: hot projectiles made from tunnel lining (rather like lava bombs from a volcano) were cast out over the hillside. These set much of the vegetation on fire and caused the closure of the A6033 road. In the clearup operation afterwards, small globules of metal were found on the ground surrounding shaft 9 - these had been melted from the tanker walls, swept up with the exhaust gases, and dropped out onto the grass.

Unable to get close enough to safely fight the fire directly, the fire brigades forced foam into ventilation shafts far from the fire. This created blockages that starved the fire of oxygen. By midafternoon the next day the inferno was no longer burning, though the fire was by no means knocked down. Petrol continued to leak from the derailed wagons through the tunnel drainage and ballast and the vapour sporadically re-ignited when it came into contact with the hot tunnel lining. It also became apparent that petrol vapour had leaked into the nearby river Roch, possibly creating explosive atmospheres in the nearby towns of Summit and Todmorden, which were partially evacuated in response.

The brigades continued to fight the fire for a further two days, until West Yorkshire fire brigade issued the stop message just after 6:30 p.m. on Christmas Eve. Fire crews remained at the site until January 7, 1985.

Of the 1.1 million litres of petrol carried by the train, 275,000 litres were rescued by the BR train crew when they drove the locomotive and the first three tankers to safety. 16,000 litres of petrol were recovered after the fire was extinguished and 900,000 litres (670 tonnes) burned.

Figure 4: Tanker 9, crowned with glassy deposits formed by bricks in the shaft above; the bricks melted, dripped down and solidified on top of the tanker.

The damage done by the fire was minimal. Approximately half a mile of track had to be replaced, as did all the electrical services and signalling. The biggest surprise was how well the brick lining had stood up to the fire. Although some bricks in the tunnel and in the blast relief shafts had become so hot that they vitrified and ran like molten glass, most of the brickwork lining of the tunnel was scorched but still serviceable. One of the photographs taken in the aftermath shows a rail tanker directly beneath shaft 9: it is crowned with a mass of vitrified slag from bricks in the shaft that had melted and dripped down (Figure 4).

Once British Rail had replaced the track and electrical services, shored up the bases of vent shafts 8 and 9 and filled the two shafts with inert foam (all this took eight months), locals were allowed a once-in-a-lifetime opportunity to walk through it before train services resumed.

The Summit Tunnel fire is worthy of note for several reasons.

• Firstly, the size of the fire: it is probably the biggest underground fire in transportation history, certainly bigger than the Channel Tunnel fire (a relatively meagre 350 megawatts) and probably bigger than the ill-defined Salang tunnel fire in Afghanistan.

• Secondly, the amazing luck of those who fought it. The BR train crew who returned to the site to rescue a locomotive and three tankers left the fire site shortly before one of the other petrol tankers filled the tunnel with flames. The firefighters in BA sets who were in the tunnel when it did fill with flames were saved by the fact that blast relief shafts 8 and 9 acted as flame vents (a function their designer never envisaged).

• Thirdly, the amount of damage to the primary structure of the tunnel was minimal, although some of the bricks melted.

At a public house in Todmorden, The Masons Arms there is a small collection of photographs noting the fire, along with the statistics of the construction, with a quotation by Stephenson, the tunnel's builder who said " I stake my reputation and my head that the tunnel will never fail so as to injure any human life"

[edit] External links

• Photographs from TV news

[edit] References

• Lindley, J. The Summit Tunnel incident, Loss Prevention Bulletin no. 134, April 1997, pp14–19
• Jones, A. The Summit Tunnel fire, Incident Report no. IR/L/FR/85/26. Health & Safety Executive, 1985
• Railway accident: report on the derailment and fire that occurred on 20th December 1984 at Summit Tunnel in the London Midland Region of British Railways, Department of Transport, 1986
• Karran, G. Research report on the Summit Tunnel fire, Todmorden, West Yorkshire on 20 December 1984, West Yorkshire Fire Service, 1985
• Summit Tunnel: A supplementary report on the vent shaft fire, 8 August 1985, West Yorkshire Fire Service, 1985
• Duncan, S. D. and Wilson, W., Summit Tunnel—post fire remedial works, 5th international symposium (Tunnelling '88), Institution of Mining and Metallurgy, 18–21 April 1988; ISBN 1-870706-01-3
• Riley, N. and Lelland, A., A review of incidents involving hazardous materials in road and rail tunnels, Proceedings of the 2nd International Conference on Safety in Road and Rail Tunnels, 1995; ISBN 0-9520083-2-7