The fire occurred at 5.50 a.m. on 20 December 1984 when a goods train carrying more than a 1,000,000 litres ... of four-star petrol in thirteen tankers entered the tunnel on the Yorkshire (north) side. One-third of the way through the tunnel, a defective axle bearing (journal 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.Read more on the Fire West Yorkshire site.