At all doors through which 3 or more drivers are hauling coal on any one shift, an attendant shall be employed on said shift for the purpose of opening and closing the doors when trips of cars are passing to and from the workings. However, in case of specially dangerous conditions, the State Mine Inspector may require in writing that an attendant be placed at doors through which less than 3 drivers pass. Places for shelter shall be provided at such doorways to protect the attendants from being injured by the cars while attending to their duties. Provided that, in any or all mines, where doors are constructed in such a manner as to open and close automatically, attendants and places for shelter shall not be required.