Procedure for isolating dangerous energy sources (electrical, mechanical, hydraulic, steam) before maintenance, with physical lock and identifying tag.
In practice
Standard practice for any electrical or mechanical isolation. The operator places a personal lock on the isolation point; the lock comes off only when that operator declares work complete. Multiple operators apply individual locks to the same point.
Regulatory detail & full definition
Essential for any work on machinery that could be re-energised. Each authorised person fits their personal lock; only that person can remove it. Multi-lock hasps allow parallel work. The corresponding tag identifies who, when, why. Prevents the common 'someone restored power without checking' fatality.