In 2022, a chemical plant in Ohio, the United States, conducted an annual overhaul. A complex production line involving reaction vessels, conveying systems, and packaging lines was shut down entirely. 14 technicians from four trades – electrical, mechanical, instrumentation, and piping – were working simultaneously in different areas. As the overhaul was nearing its end, three technicians from the electrical team completed their tasks and removed their personal locks. Then they went to have lunch. However, a welder from the piping team was still performing the final welding operation on the pipes beneath the reaction vessel.
At this time, the coordinator of the electrical team thought that everyone had completed their tasks and took out the equipment keys from the lock box – he didn’t know that although the welder’s lock was still on the lock box, the welder himself had temporarily left to fetch welding rods and did not confirm the “safety” on the spot. When the coordinator inserted the key into the isolation device to restore the power, the welder, who was on his way back, saw this scene through the window and waved his hands desperately to stop him. Almost, a fatal accident occurred.
The OSHA investigation found that the factory’s group LOTO clearance procedure lacked two key steps – “on-site confirmation by all personnel” and “final verification by the coordinator”. This was not an isolated case – in all group LOTO-related accidents, the accidents during the clearance stage accounted for more than 40%, much higher than those in single-person LOTO scenarios.
When maintenance became “a matter for a group of people”, the LOTO clearance method would undergo a fundamental change.
What is group interlock? Why are the clearance methods different?
1.1 Definition of Group Interlock
Group interlock (Group Lockout/Tagout) refers to a special LOTO procedure adopted when maintenance or repair operations are carried out by multiple authorized personnel simultaneously. OSHA 29 CFR 1910.147(f)(3) has specific regulations on this:
“When maintenance and upkeep are carried out by a group of employees, the employer must develop and implement an energy control procedure to provide each authorized employee and affected employees with protection at the same level as individual lockout or tagging devices.”
Group interlock typically occurs in the following scenarios:
Annual major overhaul or shutdown maintenance of large equipment
Overall production line maintenance (involving multiple trades and multiple isolation points)
Collaborative operations among multiple teams or departments
Joint construction by external contractors and internal teams
Continuous maintenance operations across shifts
Post time: Aug-08-2026
