PSM does not apply to normally unoccupied remote facilities (1910.119(a)(2)(iii)). The definition in 1910.119(b) has three parts, and a site must meet all of them: employees visit only periodically to check operations and do necessary operating or maintenance tasks; no employees are permanently stationed there; and the facility is not contiguous with, and is geographically remote from, all other buildings, processes, or persons. OSHA's letters give concrete benchmarks for the first two and set a high bar for the third.

What OSHA Has Said

May 29, 1998
A remote chlorine water treatment plant that qualifies
Alaska OSHA asked about a water treatment plant using one-ton chlorine cylinders, with a scrubber sized for a full cylinder. Workers based at a facility about 4 miles away spent an average of 1.5 man-hours a day there, plus 2.5 hours once a week and 6.5 hours once a month, and the site had no conveniences for a permanent presence. OSHA said it was a normally unoccupied remote facility, exempt from PSM.
Read OSHA Letter ↗
Feb 16, 2005
Gas plant vs. compressor station: the stationed-employee test
Gas plants are covered by PSM, and the exemption does not apply where employees are permanently stationed. When a former gas plant became a compressor station visited 1.5 to 2 hours a day, OSHA said it could qualify and pointed to the 1998 letter as the benchmark: if on-site time doesn't exceed about 1.5 man-hours a day and 14.5 a week, the exemption would apply. For oil and gas production sites, OSHA noted its 2000 memo not to enforce PSM pending a feasibility analysis.
Read OSHA Letter ↗
Feb 15, 2017
'Geographically remote' means far more than code spacing
OSHA said meeting NFPA separation distances does not make a facility geographically remote. Remote means that any incident at the site, including a catastrophic release, fire, or explosion, "could not affect or impact any buildings, equipment, property or employees at the plant site," and OSHA said that distance is generally much greater than NFPA spacing.
Read OSHA Letter ↗

⚡ Key Compliance Takeaway

To claim the NURF exemption, document all three tests: visit logs showing employees come only periodically (OSHA's benchmark is roughly 1.5 man-hours a day), no permanently stationed staff or the amenities that suggest them, and a separation analysis showing a worst-case release, fire, or explosion couldn't reach other buildings, processes, or people. Code-required spacing alone won't carry the argument.