 Some of the firemen allotted to the Leader complained about cramped conditions in the centre cab of the locomotive, a situation made worse by flames entering the cab from the firebox at high outputs.It was an enclosed space that was constantly hot and the single fireman's entrance door on the side of the locomotive was left open during travel to promote ventilation.The door into the fireman's cab also attracted criticism, as it would have been blocked in the event of the locomotive overturning on that side, preventing the fireman's escape, so that members of the railway trade union ASLEF threatened to stop their crews from operating the Leader.