The power supply for means of egress illumination shall normally be provided by the premises' electrical supply.
In the event of power supply failure, an emergency electrical system shall automatically illuminate all of the following areas:
1.Aisles and unenclosed egress stairways in rooms and spaces that require two or more means of egress.2.Corridors, exit enclosures and exit passageways in buildings required to have two or more exits.3. Exterior egress components at other than their levels ofexit discharge until exit discharge is accomplished for buildings required to have two or more exits.4. Interior exit discharge elements, as permitted in Section 1027.1, in buildings required to have two or more exits.5. Exterior landings as required by Section 1008.1.6 for exit discharge doorways in buildings required to have two or more exits. The emergency power system shall provide power for a duration of not less than 90 minutes and shall consist of storage batteries, unit equipment or an on-site generator. The installation of the emergency power system shall be in accordance with Chapter 27.