Wharf workers sickened by pitch fumes

Lookout! Issue 27, December 2012

Five men were affected by toxic fumes after pitch/bitumen vapour was released from a cargo vessel alongside the wharf where they were working.

The ship was preparing to unload pitch – a viscous mineral residue that is semi-solid when cool and needs to be heated to temperatures up to 200°C to become liquid enough to pump.

Pressure valve
The forward PV (pressure/vacuum) arrangement.
Maritime New Zealand ©2019

A sudden failure in the vessel’s 24 volt DC power supply automatically closed all the cargo control valves. When the power supply was restored, all of the valves opened. This, in turn, caused the liquid pitch cargo to flow from the forward to the aft tanks, causing a pressure spike in the tanks and lifting a pressure/vacuum relief valve, which then released vapour into the atmosphere.

Stevedores on the wharf inhaled toxic fumes from the vent, and had to be taken to hospital for treatment. None of the five men suffered serious harm in the incident.

LOOKOUT! Points

  • Although the ship would usually discharge its cargo of pitch on arrival, the receiver had discussed and agreed changes in the arrangements for pitch discharge and vessel loading for this visit. With any change of plans, it is important to consider any potential or new health and safety issues.
  • Management of the ship had recently changed, resulting in a change in crewing arrangements. The crew on the day had little experience in using the ship’s cargo systems and were not aware of the potential for cargo valves to fully open after a power interruption.
    • Investigation of the incident indicated that the Programmable Logic Controller (PLC) back-up battery, which maintained the system memory, had failed. Had the ship’s personnel known, they may have been able to prevent the sudden release of vapor.
    • After the incident, remedial work was undertaken on the power control system, to reduce the risk of future power cuts. The ship’s operators were also instructed to monitor the cargo temperature and pressure on a more regular basis than they had previously.
  • It is important for operators to ensure that all workers are kept safe at all times. Crew in environments involving dangerous substances must be properly educated about how to manage any risks their work might pose.
    • Since this incident, employers and staff at the port have been given medical training about the hazards involved with a ship discharging pitch. The wharf operator is also considering the use of gas-sensing devices.

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