 All trains have also been fitted with data loggers to record the driver's and guard's actions as they work the train, as well as the train's speed.Such a system had been fitted to G7, but was in the early stage of fleet roll-out, and hence had not been commissioned and switched on at the time of the accident.Rescue workers who attended the scene were impeded from accessing the trapped passengers on the train because they did not have the keys required to open the emergency exit doors.