May 31, 2023 | Susan Napier-Sewell

Utilizing the Two-Person Rule & Checklists Can Avoid Violations & Adverse Events

two-person rule

To reduce the probability of adverse incidents, electricians often work in pairs. The Lockout/Tagout (LOTO) violation described in this event may have been avoided if the two-person rule and a checklist were utilized throughout the entire evolution of the air conditioning (AC) unit installation.

This event underscores the importance of using the two-person rule and a checklist throughout procedures, and to avoid LOTO violations.

On August 18, 2020, the INL Construction Field Representative (CFR) was performing a routine walkdown of the Material Storage Building (MSB) construction site located at the Advance Test Reactor (ATR) facility. The CFR observed an air conditioning unit with a panel removed, exposing the electrical conductors. The CFR found the electrical subcontractor responsible for the installation and inquired about the condition of the unit.

The subcontractor informed the CFR the cover was removed to take a photograph to aid engineering support to complete the installation. At that time, the subcontractor was focused on the need to provide the information and had forgotten that the LOTO for that unit had been released the week prior. When the panel was removed, there was no power to the 120/208-volt unit due to both the service switch and the circuit breaker that supplies power to the unit were in the off position.

The electrician placed the power supply for the AC unit under LOTO and proper notifications were made. No one was injured or shocked due to this LOTO violation.

Figure 1: AC unit with cover removed and exposed


A human performance review was performed on the event to determine factors contributing to the active errors and latent conditions.

  • Removal of the LOTO before the installation of the AC unit was complete.
  • No verification that the AC unit was under LOTO before removal of the access panel.
  • Failure to realize the AC unit installation was not complete.
  • A missing component was noticed and identified as a priority to complete, which placed a high degree of urgency on the task.

Recommendations: Among them, use the two-person rule

When individuals are working alone on tasks that are emergent and involve critical steps such as LOTO, they are placed in error likely situations. Additionally, when projects are in their final stages, the likelihood for error dramatically increases.
• Personnel need to be reminded to slow down and utilize any and all tools available to them, such as the two-person rule before removing access panels and utilizing checklists for equipment installations and turnovers.
• Review the event with the subcontracting community and CFRs for their knowledge, awareness, and use.

Source: DOE, OPEXShare, Lesson Learned 2020-0144/Operating Experience, “Utilizing the Two-Person Rule and Checklists Can Avoid LOTO Violations and
Adverse Events
,” Idaho National Laboratory.

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Accident, Investigations
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