(4)Gas transmission and distribution facilities. The utility's gas transmission and distribution facilities shall be designed, constructed and maintained as required to reliably perform the gas delivery burden placed upon them. Each utility shall be capable of emergency repair work on a scale consistent with its scope of operation and with the physical conditions of its transmission and distribution facilities. In appraising the reliability of the utility's transmission and distribution system, the commission will consider, as principal factors, the condition of the physical property and the size, training, supervision, availability, equipment and mobility of the maintenance forces.