29 CFR §776.30

The Act applies to work on a covered interstate instrumentality or production facility even though performed during periods of temporary non-use or idleness. 52 The courts have held the Act applicable to performance of construction work upon a covered facility even though the use of the facility was temporarily interrupted or discontinued. 53 It is equally clear that the repair or maintenance of a covered facility (including its machinery, tools, dies, and other equipment) though performed during the inactive or dead season, is subject to the Acts. 54