A high-voltage isolation near miss during maintenance on a remotely operated vehicle (ROV) tether management system has highlighted the importance of independently verifying electrical isolation before work begins.
Personnel completed the required isolation and earthing procedures but applied them to the wrong system, leaving the equipment being maintained without effective electrical isolation. Although no injuries or damage occurred, the incident exposed workers to potentially severe consequences.
What happened
The Safety Flash describes an incident during planned maintenance inside a high-voltage junction box on a tether management system (TMS). Before starting the task, the ROV team intended to isolate and earth the electrical supply to the system requiring maintenance. However, the isolation arrangements were mistakenly applied to another ROV system.
Believing that the correct equipment had been secured, the team proceeded with maintenance inside the junction box.
The error was discovered only after the work had been completed. A subsequent check established that the ROV system being maintained had never been electrically isolated. Instead, it had only been switched off through the topside computer control system.
No electric shock, injuries or equipment damage occurred. Nevertheless, the team had carried out work on equipment without the intended high-voltage isolation safeguards.
The incident demonstrates how a maintenance task can proceed under the mistaken belief that hazardous energy has been controlled, even when the required isolation procedures have apparently been completed.
What went wrong
The central failure was not the absence of an isolation procedure, but its application to the wrong system. Personnel relied on verbal confirmation that the necessary isolation had been completed without independently verifying the identity of the equipment being isolated.
There was also no buddy check to confirm that isolation and earthing had been applied to the correct ROV system before maintenance began. These weaknesses allowed the team to proceed on the assumption that the equipment was electrically safe.
The distinction between switching equipment off and electrically isolating it is particularly important. Computer controls may stop equipment from operating, but they do not provide the same protection as verified physical isolation of the electrical supply.
The near miss therefore illustrates the danger of treating procedural completion as proof that hazardous energy has been removed.
An isolation procedure can be followed correctly in principle while failing to protect workers if the equipment identity has not been verified.
The big picture: Why isolation must be verified at the point of work
High-voltage maintenance requires multiple safeguards to work together, including the identification of equipment, correct isolation, earthing, communication and independent verification.
Where several similar systems operate alongside one another, the possibility of confusing equipment or isolation points deserves particular attention. This incident is especially relevant to vessels and offshore installations operating multiple electrical systems with similar configurations.
Previous incidents have exposed comparable weaknesses. In one IMCA case involving unexpected equipment start-up, a faulty circuit-breaker mechanism meant that equipment remained energised despite attempts to apply Lockout/Tagout (LOTO) controls.
Another case involving an arc-flash injury highlighted deficiencies in electrical isolation, work planning and supervision during maintenance.
Although the circumstances differed, both demonstrate why isolation must be physically established and verified rather than assumed.
The wider lesson is that electrical safety depends on the effectiveness of safeguards at the equipment being maintained, not simply on completion of documentation or receipt of verbal confirmation.
For operators, the incident raises an important question about how their maintenance systems prevent incorrect equipment identification and ensure that personnel can independently establish a safe condition before work begins.
What could have reduced the risk?
An independent verification, effective communication and stop-work authority as essential safeguards for preventing similar incidents.
For vessel operators and maintenance teams, practical considerations include:
- Verify equipment identity: Confirm the exact electrical system requiring maintenance and match it against the relevant isolation points before work begins.
- Introduce independent checks: Use a second competent person to verify the correct high-voltage isolation and earthing arrangements.
- Confirm electrical safety: Ensure that the required isolation has been applied and verified before personnel begin work inside electrical equipment.
- Maintain clear communication: Everyone involved should understand which system is being maintained, where isolation has been applied and who is responsible for verification.
- Exercise stop-work authority: Any uncertainty about equipment identity, isolation status or the effectiveness of safeguards should result in work being stopped until the issue is resolved.
These measures should form part of an effective permit-to-work and energy isolation process, supported by appropriate supervision and clearly defined responsibilities. Existing guidance on safe isolation before maintenance also emphasises the need to identify energy sources, apply suitable isolation arrangements and prove their effectiveness before work starts.
The incident provides several questions for electrical officers, ROV supervisors, engineers and safety managers to discuss:
- How do we independently confirm that an isolation applies to the exact equipment being maintained, particularly where several similar systems are installed?
- What safeguards prevent work from proceeding when an isolation has been verbally confirmed but not physically verified?
- How do we distinguish between equipment switched off through a control system and equipment safely isolated from its electrical supply?
- If personnel discover uncertainty about an isolation immediately before maintenance, what ensures that work is stopped and the concern is resolved?
Key takeaways
- Correct system identification is fundamental: Isolation applied to the wrong equipment provides no protection to personnel working elsewhere.
- Verbal confirmation is not independent verification: High-voltage isolation and earthing arrangements must be checked against the actual equipment involved.
- Switching off is not isolation: Computer-controlled shutdown does not establish an electrically safe working condition.
- Independent checks provide an additional safeguard: Buddy checks can help identify errors before personnel are exposed to hazardous energy.
- Near misses reveal weaknesses before an injury occurs: This case provides an opportunity for operators to review how isolation arrangements are verified across their fleets.