91. (1) An employer shall ensure that a substation or a main switch room is—

(a) suitably constructed,

(b) arranged, so far as is reasonably practicable, so that no person can obtain access thereto otherwise than by the intended entrance,

(c) arranged, so far as is reasonably practicable, so that a person cannot interfere with the equipment or conductors therein from outside,

(d) provided with efficient means of ventilation and kept dry if under cover, and

(e) as appropriate to the tasks being undertaken, under the control of an authorised person or authorised persons.

(2) An employer shall ensure that only an authorised person or a person acting with his or her consent, or under his or her supervision, can enter any part of a substation or switch room in which there may be danger.