As UK MAIB reports in its most recent Safety Digest, a container ship was on passage. In the engine room, the electrician was pondering how to repair a fault with the ship’s ballast water treatment system (BWTS), which needed to operate on arrival into port the next day.
The incident
The power supply to the BWTS could not be reset, leading the electrician to believe the fault might lie with the circuit breaker. The defect only emerged after that morning’s work planning meeting. The electrician started their investigation anyway, opening the panel on the main switchboard to gain access to the circuit breaker. The chief engineer (C/E) observed this and instructed the electrician to close the panel and refer to the electrical drawings to try to
identify the source of the problem. A short time later the C/E found the electrician still working in the switchboard. Repeating the instruction to
the electrician not to work inside the panel, the C/E went to eat lunch.
The circuit breaker was designed to be removed without the need to isolate the base unit; however, the electrician was unfamiliar with this arrangement and had loosened one of the live connections on the input to the base unit. The electrician used rubber gloves to insulate themself from the live 440 volt (V)
alternating current terminals when working on the connections.
After the C/E left the engine room, the electrician tried to reconnect the cables to the base unit using a socket extension on the head of the bolt and a spanner to hold the nut in position at the rear of the connections. As the electrician tightened the bolt on the live input connection, the nut rotated and the steel spanner touched an uninsulated copper conductor on the adjacent circuit breaker base unit. This caused a short-circuit between two phases of the
switchboard. The short-circuit caused a high current to flow, vaporising the copper conductor and part of the spanner in an arc flash creating extreme
heat and blinding light. A burst of hot gas and molten metal exploded from the panel onto the electrician’s face and chest.
The ship’s engineers were alerted to a problem with the switchboard when the remote machinery alarm system sounded in the mess room. As the engineers headed to the engine room, the electrician arrived on the ship’s bridge with serious burns to their face and chest. The following day, the electrician was
transferred to hospital for medical treatment and later repatriated to recuperate at home. There was significant damage to the ship’s main switchboard.
Lessons learned
- Risk → Taking the time to fully understand the arrangement of the circuit breaker and base unit assembly would have enabled the electrician to safely remove the circuit breaker and reduce the risk of injury or death to an acceptable level. The safest equipment to work on is that which is not live; in this case, the arrangement of the circuit breaker and base unit meant that it was unnecessary to disconnect the cables.
- Plan → Working alone without a permit to work, LOTO procedure or agreed safe system of work increases the risk of an accident. The work was unexpected and therefore not included in the day’s planning meeting. New work requires a new plan, regardless of time pressures. Maintenance or repairs to live equipment must undergo thorough risk assessment before starting work and, in all cases, should only be completed in exceptional circumstances and under the strictest control.
- Observe → This accident was avoidable because there were opportunities to stop the work and reassess the risks. Everyone has a responsibility to be alert to what is happening around them and should feel empowered to intervene and stop any work that raises safety concerns.
- Equipment → Working near live electrical equipment requires specific tools and PPE. The use of uninsulated tools while working in a live switchboard invited a short-circuit and the electrician, who was not wearing face protection, was lucky not to lose their eyesight in the accident.
