Drainage Pot Pressure Increase Blows Up and Kills Crew

By
Mfame Team
-
7514
Vessel : Tanker.
Location : Drifting Close to Anchorage.
Casualties : One.

Incident:

The third engineer was taking his routine watch keeping rounds, which includes draining accumulated water (condensate) from the main and auxiliary air receivers.  He opened each of the two inline drain valves which were located in front of the main air reservoir.  He opened them about one turn and stood by watching the flow of condensate through the observation glass of the drainage pot.  All of a sudden, the observation glass exploded.  The third engineer was seriously injured, breathing without consciousness.  The Oiler noticed the scenario and immediately raised the alarm.  He shut down the two air receiver drain valves to stop the flow of escaping air and administered first aid to the victim.  Not responding to the first aid effort, the victim stopped breathing within 30 minutes time.  Cardiopulmonary resuscitation was immediately performed by crew members.  Shortly after that paramedics arrived by helicopter and assessed the situation, but it was too late; the victim was confirmed dead.

Air-Bottle-Drain-arrangement.png

Investigation:

  1. The condensate had accumulated in the air receiver overnight.
  2. When the drain valves from the main air receiver were opened, the condensate flowed into the drainage pot in sufficient quantity to cover the bottom of the pot and the discharge hole.
  3. This flow of liquid was probably followed by a marked increase in pressure due to the inrush of pressurised air (about 30 bar) from the receiver.Air-Bottle-condensate-pot.png
  4. The pressure increase in the drainage pot was sufficient to fracture the observation glass, leading to its catastrophic failure.
  5. The positioning of the drain valves behind the observation pot meant that the third engineer’s upper body was positioned directly over the observation glass and therefore in the path of the explosive force and debris from the pot.
  6. The condensate drain pots fitted on the vessel had a modification that was implemented for ease of observation and it was not in conformance with the original yard delivery specification and drawings.
  7. The modified drainage pots and the enclosed drain system should have been brought to the attention of class by the shipyard and subject to design scrutiny prior to being installed and used, as this was both a modification and exposure to pressures in excess of 7 bar.

Note: When in doubt, consult the Class.

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Source: UK P&I