(a) Any residential accommodation for persons voluntarily or involuntarily residing, on a temporary or long-term basis, in a building owned, leased or rented by the Federal Government;

(b) Portions of Federally owned buildings leased, rented or otherwise provided in their entirety to non-Federal parties;

(c) Places of employment in the private sector or in other non-Federal Governmental units that serve as the permanent or intermittent duty station of one or more Federal employees; and

(d) Instances where an agency head establishes limited and narrow exceptions that are necessary to accomplish agency missions. Such exceptions must be in writing, approved by the agency head and, to the fullest extent possible, provide protection of nonsmokers from exposure to environmental tobacco smoke. Authority to establish such exceptions may not be delegated.