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H2S detected in a bilge tank

During routine transfer of bilge water from engine room bilge wells to the bilge water tank, the crew noticed the smell of “rotten eggs” from the bilge tank vent.  Immediately the transfer was stopped.  During measuring the vent pipe with the Dräger multi-gas meter it was confirmed 453 ppm of H2S (Hydrogen Sulphide) was detected.

Preventive actions were taken to ensure the gasses did not enter the accommodation. The quick response of the vessel crew prevented a serious accident.

The immediate hazard was of a dangerous or even lethal atmosphere (High H2S concentration).  Seawater in (bilge) tanks, especially in the engine room, mixed with various residues and biodegradable detergents are a perfect place for the development of dangerous levels of H2S.  Failure to recognize the dangers could have resulted in explosion, intoxication or even loss of life.

What went wrong?

  • Technical
    • Bilge tank had not been dealt with or emptied for a longer period – it had not filled up;
    • Regular inspection of the tank was not easily possible;
    • Several corners of the tank had built up (stone) residue, which was not easily removed.
  • Organizational
    • Lack of knowledge: during the communication with external parties it was found that some parties were uncertain how to handle the removal of the sludge from the tank without contaminating the atmosphere of the surrounding ER spaces; 
    • The on-location specialist was occupied and not able to assist immediately;
    • There was not a suitable berth available for tank cleaning;
    • The required vacuum and ventilation equipment were not available and there was a delay of some days before the final removal of sludge and tank cleaning.

 Actions taken

  • Stopped the transfer (“Stop the Job”);
  • Measured the H2S concentration;
  • Informed emergency response team and client;
  • Connected flexible hose to vent pipe to route gasses away from the accommodation;
  • Requested assistance from local agencies on removal of the bilge residue and tank cleaning;
  • Constant monitoring by measuring device with crew in full respiratory protection;
  • Removal of Bilge water and cleaning of the tank by a specialized company;
  • Gas free certificate issued.

Lessons learned

  • Review of vessel machinery cleaning practice;
    • Clean machinery spaces with detergents when the ship is in port, preferably using fresh water
    • Check if use of bio-degradable detergents are necessary or possibility for replacement additives and cleaning agents

Members may wish to refer to:

Safety Event

Published: 25 November 2021
Download: IMCA SF 32/21

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