Closure device
Closure device means a cap, hatch, lid, plug, seal, valve, or other type of fitting that prevents or reduces air pollutant emissions to the atmosphere by blocking an opening in a cover when the device is secured in the closed position. Closure devices include devices that are detachable from the cover (e.g., a sampling port cap), manually operated (e.g., a hinged access lid or hatch), or automatically operated (e.g., a spring-loaded pressure relief valve).
Source
40 CFR § 63.681
Scoping language
All terms used in this subpart shall have the meaning given to them in this section, 40 CFR 63.2 of this part, and the Act.