My reasoning is that the employer has only control to any extent over the unit he occupies and not the common areas.
As they used to say in the union meetings, "Point of information" In a multi-Occ the employer has the duties of a RP in the workplace under his control, which includes part of the common areas. Check out definition of a workplace.
Art 2 "workplace" means any premises or parts of premises, not being domestic premises, used for the purposes of an employer's undertaking and which are made available to an employee of the employer as a place of work and includes,
(a) any place within the premises to which such employee has access while at work; and
(b) any room, lobby, corridor, staircase, road, or other place,
(i) used as a means of access to or egress from that place of work; or
(ii) where facilities are provided for use in connection with that place of work, other than a public road.