A normally unoccupied remote facility, or NURF, is an OSHA term, not an IEC 61511 one. It describes a process facility that is operated, maintained, or serviced by employees who only visit periodically, with nobody permanently stationed there, and that is geographically remote from other buildings, processes, and people. Think of an unmanned wellpad, a remote pump station, or a small water treatment skid sitting out on its own.
The term matters because OSHA’s process safety management standard (PSM), partly exempts a NURF from certain PSM requirements. The catch is the “normally unoccupied” part, and OSHA never put a hard number in the rule. In one well-known interpretation letter, OSHA accepted a water treatment plant that employees visited for about 1.5 man-hours a day, plus a couple of hours weekly, as normally unoccupied. That 1.5-hour figure is the rule of thumb people reach for, but it is guidance from a letter, not a bright line, and the “geographically remote” test still has to hold, meaning a release, fire, or explosion there could not reach the main site.
In our experience at SIL Safe, one industry that often lands here is biogas facilities. They tend to be relatively small, highly automated, and run with little or no one permanently on site, so they fit the normally unoccupied profile and may trigger the NURF exception.
More broadly, this is a growing trend. As automation has improved, with PLCs becoming far more capable at a much lower cost and SCADA systems getting cheaper and easier to set up, more plants can be monitored and operated from a distance, sometimes from another state or even another country. That shift pushes a steadily larger set of facilities toward the kind of unmanned, remotely run operation the NURF exception was written to address.
Key Points
- Defined in OSHA’s PSM standard, 29 CFR 1910.119, not in IEC 61511.
- Employees only visit periodically and none are permanently stationed on site.
- Must be geographically remote, so an incident there cannot affect other buildings or people.
- OSHA’s roughly 1.5 man-hours-per-day example is guidance from an interpretation letter, not a fixed threshold.
Example
A remote injection-water pump station that a technician drives out to for about an hour each morning to check operation, with no one else on site and the nearest occupied building a mile away, is the classic NURF. Because of that, the operator may apply the normally unoccupied remote facility provisions rather than treating it like a fully manned plant.
Cited Sources
- OSHA 29 CFR 1910.119 — Process safety management of highly hazardous chemicals (applicability and definitions).
- OSHA Standard Interpretation, May 29, 1998 — PSM exemption for a normally unoccupied remote facility (water treatment plant).