200803 Serious burns from boiler blasts

Source: Marine Occurrence Investigation Number 238, Australian Transport Safety Bureau, Canberra, 16 November, 2007 (www.atsb.gov.au).

While awaiting berth, the ship's engineers were engaged in replacing the auxiliary boiler burner with a clean spare burner. The third engineer followed all safety precautions before replacing the burner, including running the forced draft fan for a few minutes to purge the furnace. He then fired the burner three times but it failed to ignite. He purged the furnace again for several minutes before starting to remove the burner to inspect it. A few minutes later, there was an explosion. The engineer suffered burns to his face and body.

The chief engineer then purged the boiler furnace for about an hour after the incident. With the second engineer, he then removed the burner to inspect it. Moments later a second explosion left both of them with burns to their faces, hands and bodies. All three engineers were airlifted from the vessel to hospital. Two of them needed repatriation.

The investigation by the Australian Transport Safety Bureau found that both explosions resulted from flashback from the furnace caused by the ignition of fuel vapour by the residual heat in the boiler's refractory material and furnace walls. Although the furnace had been purged for an hour using the forced draught after the first explosion, this was not enough because the number of unsuccessful attempts to ignite the burner meant that liquid fuel may still have been in the furnace even after a lengthy purge and the furnace may still not have cooled sufficiently.

The investigation also revealed that there had been previous incidents on ships fitted with the same type of boiler/burner combination, including a similar flashback explosion on the same vessel about five years earlier. A similar incident on another vessel four years earlier was investigated by the bureau, which recommended that the makers of this type of boiler provide a safety bulletin drawing attention to the correct safety procedures when servicing the burner unit.

Unfortunately, the manufacturer's safety bulletin and caution plates – which were supposed to be fitted near the boilers – did not reach the vessel, due to a change in managers. In the latest incident, while the second and third engineers were vaguely aware of previous boiler flashback explosions on the same ship or another ship in the fleet, neither the chief engineer nor the master was aware of any previous incident.

Despite the fact that a similar incident had occurred on board the same ship, all of the hazards associated with servicing the boiler burner had not been identified. There were also conflicting guidelines on how long a furnace had to be purged following a burner misfire.

Corrective actions
The boiler manufacturer has since begun redistributing the safety bulletin and caution plates – this time with the assistance of classification societies to ensure its mailing lists are comprehensive.
The manager has confirmed that the manufacturer's caution plates have been received and fixed to the oil-firing unit and boiler control panel.
The oil-firing unit has also been modified with safety features to reduce the risks of flashback explosion following a burner misfire.