UK MAIB: Electrician injured in explosion

An electrician was badly injured while working on a switchboard. The circuit breaker was designed to be removed without the need to isolate the base unit (Figure 1).

Fig. 1: The circuit breaker arrangement

However, the electrician was unfamiliar with this arrangement and had loosened one of the live connections on the input to the base unit (Figure 2).

Fig. 2: The base unit connections

The electrician used rubber gloves to insulate himself from the live 440 V alternating current terminals when working on the connections.

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 (Figure 3).

Fig. 3: Reconstruction of the accident

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 (Figure 4).

Fig. 4: Position of the electrician

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 the face and chest.

The following day, the electrician was transferred to hospital for medical treatment and later sent home.

There was significant damage to the ship’s main switchboard.

• The electrician twice disobeyed clear instructions from the chief engineer, to not work in the switchboard.
  
  
• The electrician was not familiar with the arrangements within the switchboard – had he taken the time to fully understand the arrangement of the circuit breaker and base unit assembly, that would have enabled the electrician to safely remove the circuit breaker and reduce the risk.
  
  
• The electrician was working alone without a Permit to Work, lock-out/tag-out arrangement or a safe system of work. The work was unexpected and therefore not included in the day’s planning meeting. New work requires a new plan, regardless of time pressures.
  
  
• 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 his eyesight.