Enhancing Lockout/Tagout (LOTO) Safety During Machinery Maintenance: Development of a Fail-Safe Personnel Verification System to Prevent Unexpected Start-up

Abstract:

Unexpected machinery start-up during maintenance remains a significant occupational safety concern, particularly when several workers are required to enter a hazardous machine zone. Lockout/Tagout (LOTO) provides the primary means of controlling hazardous energy; however, the final stage of the procedure still requires confirmation that all employees have been safely removed before energy is restored. This study proposes a fail-safe personnel verification system that adds an engineering control to the conventional LOTO process. A discrete-event simulation of an automated conveyor maintenance cell was developed using Python. The model represented 10,000 maintenance cycles, three authorized maintenance workers, two controlled access points, individual personnel identification, zone-occupancy monitoring, system-health verification, and a restart interlock. The simulation included normal maintenance, incomplete personnel exit, unauthorized entry, sensor failure, communication failure, controller failure, power interruption, false exit signals, and restart attempts during maintenance. A total of 30,000 personnel-state events were evaluated. The simulated system achieved 99.82% personnel-state verification accuracy and a mean detection latency of 184 ms. Of 1,000 unsafe restart attempts, all were inhibited. Eighteen valid restart events were unnecessarily inhibited, producing a false-inhibition rate of 1.80%. Eighty fault-injection events were also evaluated, and all resulted in a safe state. Under the same simulated assumptions, the conventional verification model produced 17 incorrect restart authorizations. The results indicate that automated personnel verification can provide an additional engineering barrier against unexpected start-up, particularly during multi-person maintenance. The proposed system is intended to supplement, rather than replace, established LOTO procedures.