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Ask the way you'd ask a colleague. The answer comes from your own documents, with the source right there.
QuestionQuestion · how often must a lone worker check in
A lone worker must check in with the Control Room every 4 hours during their shift (and again at the end of the shift, once they have left the building and locked up), as set out in the Lone Working Procedure (NFS-HS-006). The Site Supervisor may set a shorter interval if the task is more hazardous or the site is remote. This 4-hour rule is confirmed consistently in the Lone Worker Check-in Log (NFS-FRM-004), the Staff Handbook (NFS-HR-001), and the Lone Working Risk Assessment (NFS-RA-003).
Sources
NFS-HS-006 · Lone Working Procedure
NFS-FRM-004 · Lone Worker Check-in Log
NFS-HR-001 · Staff Handbook 2026
NFS-RA-003 · Lone Working Risk Assessment