Refrigerated Seawater Systems on Fishing Vessels

The recent tragic death of two fishermen on board a fishing vessel has prompted the Health and Safety Authority to issue this Safety Alert. It appears that both men were overcome by toxic gases when they entered a fish tank. Seawater contaminated with fish residue in the Refrigerated Sea Water (RSW) system is a source of such toxic gases.

RSW systems normally recirculate Sea Water (SW) through a SW pipe system, via a cooler and into a RSW fish tank. Typically such systems may lie unused for a number of months, this can allow toxic gases to build up over time and accumulate in the Refrigerated Sea Water (RSW) pipe system. Toxic gases can be released from contaminated sea water into the fish tank when such systems are being flushed out in preparation for use.

Toxic gases given off by contaminated seawater include hydrogen sulphide, hydrogen cyanide, ammonia and others. The fish tank would be classed as an enclosed / confined space.

Picture of a Trawler that may use an RSW system

Picture of a trawler

Flushing and Cleaning of Refrigerated Sea Water (RSW) systems.

  • Ensure proper cleaning and flushing of RSW system after use, removing all fish residues. This should be carried out in clear water using recommended cleaning agents.
  • On no account open or enter RSW tanks known to contain seawater / decaying fish, unless full procedures for safe entry have been carried out.
  • Ensure adequate ventilation exists in spaces adjacent to RSW tanks.

Enclosed / Confined Space

Confined Space means any place that by virtue of its enclosed nature creates conditions which give rise to a likelihood of accident, harm or injury.

Identification of all relevant enclosed spaces on board is a critical step in preventing potential danger. Special attention must be given to tanks/holds where processes may result in dangerous atmospheres being present such as a result of maintenance or the decaying of fish or other organic matter.

In the past many confined space accidents have occurred where colourless and odourless gases were present in the air. Thus there was no obvious smell or visible indication that the space was dangerous prior to entry. Low oxygen levels for example can cause instant loss of consciousness. Oxygen deficiency and hazards can arise in enclosed spaces from

  • rusting in tanks, voids,
  • operating generators, engine driven pumps or any internal combustion engines in or near these spaces,
  • flammable atmospheres,
  • hot-work or oxygen enrichment.

Once the enclosed spaces have been identified, appropriate measures must be taken to ensure all persons are aware of the areas involved and the relevant precautions to be taken when work needs to be carried out in these enclosed spaces.

Stringent health and safety procedures must be in place when entering such confined/ enclosed spaces. These procedures should include:

  • atmospheric testing and monitoring,
  • effective ventilation including mechanical ventilation as necessary,
  • arrangements for rescue and the wearing of suitable breathing apparatus,
  • training in such matters is necessary for persons who enter confined spaces.(see Code of Practice for Working in Confined Spaces below).

The Ship’s Safety Statement (link) must be updated to include confined space identification and controls prior to entry.


Further information

Previous Alerts

November 2015