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It is very difficult to imagine what happens when a train derails at speed and the world goes mad – here is Hatfield in slow motion plus an analysis of how the Mk 4 performed
Oxlease Road Bridge provides the reference point for the Hatfield derailment site. Measured from the north face of the bridge, the first rail break is at 43.7m and the derailment area extends to 72m. Marks on the left hand wheelsets of the leading Class 91 locomotive suggest that it hit a rail already broken. With the train running at 115-117mile/h the tragedy unfolds.
*Locomotive plus coaches A and B remain on the rails after passing over the derailment area.
*But as the rail progressively fractures under the impact of passing wheels, coaches C,D,E,F and G derail. At this point the couplings hold but bogies start to detach
*Coach C hits and demolishes a signal post.
* As the bogies of coaches G (service vehicle) and H start to displace, centrifugal force plus the shoulder of the ballast on the down slow line cause the coaches to roll to left.
*Coach G rolls onto its side.
*At some point during Coach G's roll through 90 deg the coupler between it and coach F uncouples, opening the airpipe and initiating full braking.
*The coupler between coach H and Coach M pulls out as drag-box pin fails under an estimated 150tonne load.
*After slowing at twice the retardation of the rest of the train, coaches H and M plus the Driving Van Trailer come to a halt. H is separated and almost on its left and side. M and the DVT are upright but derailed.
*Meanwhile the Service Vehicle, still sliding on its side swings outwards and, traveling at an estimated 86.3mile/h, hits an Over Head Line Equipment support. The H shaped beam of the mast has its two faces aligned with the track so that the sharp edges cut into the roof structure.
*Despite the first impact, Service Vehicle is still traveling at 73mile/h when it may have hit a second OHLE support mast.
*The Class 91 locomotive and coaches A-G come to rest. The locomotive is 649m from the bridge.
Coaches A and B are upright. C is leaning slightly, with one end on the down fast and one in the cess, and shows signs of damage from hitting a trackside structure as does D which is upright and sitting in the cess. E is also leaning slightly and at an angle to the track. F is nearly on its side and G is on its side with the roof at the rear crushed and up against an OHLE support.
In its first high energy accident the Mk 4 body shell protected its passengers well, despite a less sophisticated construction than the Mk 3 with its impressive crashworthiness record.
Of the four fatalities in the service vehicle (coach G), all you can say is that they were desperately unlucky. The parting of the coupling between Coach G and coach H allowed the ‘tail' of the front section of the train to swing out and the rear coaches to roll over before hitting the OHLE masts with their waiting sharp edges.
My theory for the reason why the couplers may have parted is in the box.
Coaches A to F suffered ‘little significant internal damage', essentially some areas of loose trim and a number of detached seat cushions, despite two of them hitting trackside equipment. There was minor damage to some seats and tables in coaches H and M which decelerated the hardest. Even so, this damage was restricted to detached table legs, damaged seat cushion attachments and malfunctioning ‘tilt mechanisms'. Commendably, no internal fixtures and fittings had broken free.
Passenger injuries reflected this performance, becoming more severe along the train. Bruising in coach A, became back and neck injuries in Coaches B and C, possibly due to whiplash. Coaches D, E and F derailed, resulting in more serious impact and bruising injuries. Passengers in Coaches H (which partially overturned) and M suffered more severe injuries including fractures and whiplash. The interior of the Service Vehicle was severely damaged
Did the deflector act as a drag brake?After the Polmont accident in Scotland in 1984 – where the driving coach on a push pull train hit a cow and pitch-poled end over end – passengers were banned from the front coach of multiple units running at over 100mile/h. To reduce the risk of a repeat accident, all future driving trailers had to be ballasted up to increase the axleload on the front bogie and have an obstacle deflector fitted under the nose of the vehicle. Said obstacle deflector had to meet some very demanding load absorption specifications. It is a vertical steel plate in front of the bogie, hinged at the top and held in place by shock absorbers attached to the bottom edge to provide the necessary resistance as the plate swings backward. Under emergency braking, the latest rolling stock can achieve a retardation of 12%g (g = the acceleration due to gravity) The leading portion of the train at Hatfield, including Coach H on its side hitting possibly two OHLE supports, slowed at 31%g, according to HSE figures. But based on the speeds and stopping distance the rear three vehicles of the IC225 slowed at 60% g after they separated from the remainder of the train when the couplers between coaches G and H failed. This difference in deceleration supports the theory, proposed by engineering informed sources, that the obstacle deflector on the derailed DVT, may have dug into the ballast of the adjacent track and acted as an additional brake. This could also explain why the coupling pulled out. The HSE told me that this possibility is being considered. |