Description of Incident
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); 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). 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).
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).
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.To view this IMCA safety alert in full, click the 'Download Alert' button above and refer to section 4 of the document.