Closures in the air distribution system shall be considered. If one or more spaces of several arranged in parallel can be closed off from the source of the refrigerant leak, their volume(s) shall not be used in the calculation.
Exceptions: The following closure devices are not considered:
1. Smoke dampers, fire dampers, and combination smoke/fire dampers that close only in an emergency not associated with a refrigerant leak,
2. Dampers, such as VAV boxes, that provide limited closure where air flow is not reduced below 10 percent of its maximum (with the fan running).