What is the required free area for permanent openings to obtain ventilation air from outdoors for appliances located in unconfined spaces?

The correct answer aligns with the requirements set forth for ventilation air necessary for combustion appliances located in unconfined spaces. The standard specifies that for each unit of input capacity of the appliance (measured in BTUs), a certain free area for air openings is needed to ensure adequate ventilation.

In this case, the specified value of 1 inch of opening per 5000 BTU is designed to ensure that there is sufficient airflow to support proper combustion and to prevent hazards associated with insufficient oxygen levels. This ratio is part of the design considerations to support combustion efficiency while maintaining safety within the facility.

The other options represent ratios that may not provide the same level of air exchange, which could potentially lead to operational inefficiencies or unsafe conditions in settings where combustion appliances are used. This makes the 1 in per 5000 BTU requirement the appropriate standard for ensuring adequate ventilation in unconfined spaces.