The 07:40 Bedford - St Pancras on the 12th June '68 was formed of a 4-car Class 127 (leading) and two 2-car Class 112s. The train ran normally until some time after leaving Harpenden, when running at about 65mph, severe vibration became apparent under the seventh coach. Almost at once there seemed to be a minor explosion and seconds later the vehicle became full of choking smoke and fumes, while smoke & fumes emanated from the underside of both rear coaches. As the train slowed down passengers began to jump and all had left the coaches soon after the train was stopped by the action of the driver, guard and operation of the alarm signal.
Unfortunately, two were killed and ten others injured by jumping out when the train was still moving. The report into the incident felt that there would have been no casualties had they waited for the train to stop, but not surprised that in the conditions that the passengers misjudged the earliest moment at which it was safe to jump, possibly because of the pressure of other people behind them. This was not helped by the low density layout of the Cravens vehicles.
In the investigaton afterwards, the CM&EE dept. determined that lack of lubrication was to blame, with an oil filler pipe screw cap missing. The gearbox had totally seized, causing both input and output shafts to come to a sudden stop. The engine itself was protected by the fluid flywheel, but the driving wheels continued to turn the seized output shaft. This caused the gearbox casing to tear away from the right hand side mounting brackets. The cardan shaft, thus freed at the forward end, started to flail and ruptured the main fuel tank. At the same time the output end broke away from the gearbox, spilling out the grossly over-heated internal parts; assisted by sparks from the flailing shaft, this was enough to ignite the fuel.
The investigation showed that there was no justification for locating the main fuel tank around the cardan shaft and a simple tank near the non-driven bogie would have been suffice. In fact by August '69, before the report was published, all the remaining vehicles of this type had this modification completed. The passengers critisised the absence of lower step boards, and the positioning of the alarm signal chains, none of which were located in the passenger saloons. The nine sets remaining on Kentish Town - Barking services were being fitted with these lower footsteps to one door on each side and two additional points of access to the alarm signal at the time of the report. These alterations to the fuel tanks, footsteps and alarms were done despite the Class 112 sets being withdrawn just weeks after the report.
The Class 127s also had some of these modifications done.
Sandridge (near St.Albans), LMR
Involving Class 112 / Class 127