This proposed addendum deletes Section 4.1.2 Alternative Ventilation which allows for 'other methods' to be used to provide the required ventilation rates but provides no guidance. The proposed addendum adds a new Section 4.6 Equivalent Ventilation which along with a new definition for annual exposure provides a basis for alternative ventilation system designs by requiring that they provide the same or lower annual exposure as would be provided by complying with Section 4.1.