Aren’t all doors on a train able to be physically opened (i.e. pulling them apart) in an emergency? The doors being out of service for passenger use surely does not mean the doors are physically incapable of opening?
Only open the doors in emergency via the egress handle, which should apply the brakes and bring train to a stand before the doors can be released, otherwise any idiot could be pulling at the doors to open them.
If the doors are out of use there's a problem, you don't want a door accidently opening en-route and losing someone. So doors are locked out of use, locked shut, so can't be opened and if all doors in that vehicle are locked OOU then the vehicle must be locked OOU and not available for passenger use.