(1) If the TWH facility or building has a mechanical ventilation system, the operator shall maintain it according to the manufacturer's specifications and operate the system to provide fresh and filtered air. The operator shall have building maintenance staff or mechanical ventilation system contractors set the system to increase ventilation or the percentage of outside air that circulates in the facility or building and verify the following:

(a) The mechanical ventilation system is fully functional.

(b) The mechanical ventilation system filters have a minimum efficiency reporting value (MERV) rating of at least 13 or equivalent. If the mechanical ventilation system does not support MERV 13 filters, use the highest MERV rating filter supported by the mechanical ventilation system.

(c) The mechanical ventilation system's outdoor air intake is maximized. Reductions in outside air intake may be made when external conditions pose health and safety risks to the occupants.

(d) Maintenance checks occur at the beginning of each growing season when preparing buildings to be reopened. Additional maintenance checks must occur based on manufacturer recommendations, usually quarterly or annually.

(e) Ensure written maintenance records are maintained. The written record must include documentation of filter selection, including a selection reason if less than MERV 13 filtration is used, and filter conditions. Written records must be available for review upon request by the state agency representatives.

(f) Filters in any mechanical ventilation system used in a TWH facility or building must be in good repair and replaced in accordance with manufacturer's instructions.

(2) The operator shall instruct occupants in housing with mechanical ventilation systems to:

(a) Turn on mechanical ventilation systems whenever the TWH facility or building is occupied; and

(b) Temporarily shut down the mechanical ventilation system when external conditions pose health and safety risks to occupants.

(3) In buildings without mechanical ventilation systems, the operator shall instruct occupants to close windows and other outside openings when external conditions pose health and safety risks to occupants.