In 2023, a paper mill in Wisconsin, the United States, witnessed a tragic accident. A maintenance technician completed the maintenance work on the No. 2 paper machine, removed his own lock and label as per the procedure, and then closed the main power circuit breaker. However, he was unaware that his colleague had removed the safety curtain in the roller area during the maintenance period for “convenience”, while another operator was cleaning the pulp residue in the roller gap. At the moment the equipment started, the rotation of the rollers pulled the operator’s arm into it, causing severe crush injuries.
The conclusion drawn by OSHA after the investigation is intriguing: The LOTO dismantling procedure itself is not flawed, but there are at least five key inspection steps missing from “dismantling the lock” to “reconnecting the power supply”. This is not an isolated case – according to OSHA’s statistics, approximately 30% of all LOTO-related accidents do not occur during maintenance operations, but rather during the transition period when the equipment is being restored to operation.
Appendix A of OSHA further clarifies the five-step process for “restoring equipment to operational status”:
Step 1: Inspect the machine and the surrounding area to ensure that all unnecessary items have been removed and that the equipment components are functioning properly. Step 2: Check the work area to ensure that all employees have been safely positioned or removed. Step 3: Verify that the controller is in the neutral position. Step 4: Remove the locking device and re-energize the machine or equipment. Step 5: Notify the affected employees that the repair is complete and the equipment is ready for use.
Pay attention to the third step – “Verify that the controller is in neutral position” – this is an independent step that many people overlook. If the start button is still in the “ON” position and the circuit breaker is closed, the equipment will start instantly. At this point, if someone is still in the dangerous area, the consequences could be unimaginable.
1.2 According to the provisions of GB/T 33579-2017
The Chinese national standard GB/T 33579-2017 “Mechanical Safety – Methods for Hazard Energy Control – Lockout/Tagout” stipulates in Step 7 “Release and Restoration” as follows:
After the work is completed, count the personnel and tools, notify everyone, and then follow the principle of “who locks, who unlocks”. The person in charge should remove the locks/tags one by one, and finally restore the power.
Standard Appendix C provides further specific examples of the procedures for restoring services:
Inspect the machine and the adjacent areas around it to ensure that all unnecessary items have been removed and the machine components are operating as they should;
Check the working area to ensure that all employees are in a safe area or have left the working area;
Remove the locks and interlocking clasps from the isolation device one by one, and push the isolation device to the “ON” position;
Notify the affected employees that the maintenance is complete and the machine can be used for production.
Core principle: From the removal of the last lock to the closing of the first power supply, the complete “pre-power-on checklist” must be carried out. Any skipping can lead to an accident.
Case 1: Equipment started immediately due to the controller not being reset
Accident details: In 2021, at an automotive parts factory in Michigan, USA, maintenance personnel completed the maintenance of a press machine and removed the LOTO device. During the maintenance period, the operation mode switch was changed from “manual” to “automatic” to test a certain function, but it was not switched back after the test. When the maintenance personnel turned on the main power supply, the press machine immediately started at full speed in automatic mode, and a worker who was cleaning the mold area was severely crushed.
Cause of the accident: The controller’s position was not checked before powering on.
Lesson: The third step in Appendix A of OSHA, “Verify that the controller is in neutral position”, is not a suggestion but a legal requirement.
Case 2: Failure of protection due to unrestored safety interlock
Accident details: In 2022, a plastic injection molding factory in Zhejiang Province, China, the maintenance personnel repaired the hydraulic system of the injection molding machine. During the maintenance, to facilitate operation, the interlock switch of the safety door was bypassed. After the maintenance was completed, the maintenance personnel removed the LOTO device and restored the hydraulic energy, but forgot to restore the safety door interlock. The operator opened the safety door to clean the spilled material while the equipment was running. The equipment did not stop, and the operator’s hand was injured by the mold.
Cause of the accident: The safety protection device was not reset before power was connected.
Lesson: The bypass and recovery of safety interlocks must be documented, and each item must be verified before power is applied.
Post time: Jul-28-2026
