The Norwegian Maritime Authority (NMA) has issued an update for transporting biological liquid cargo following explosion after hot work was carried out near a vent from a tank containing fish silage.
Fish silage is fresh fish residue and formic acid. The acid conserves the residue and delays the process of decomposition. When organic material decomposes in environments where there is little air, hazardous gases may form.
In an accident in the summer of 2024, work was carried out with an angle grinder near a vent from a tank containing fish silage. Silage had been stored in the tank in warm summer weather for a couple of weeks. Spark(s) from an angle grinder then most likely ignited a gas developed in the cargo. This led to an explosion where the hatch was torn loose and thrown many metres up in the air before it landed in the sea behind the boat. Thankfully, none of the crew members were badly injured, but it could have gone much worse.
The Norwegian Maritime Authority (NMA) has received other notifications on crew being exposed to hydrogen sulphide (H2S) when transporting fish silage or other liquid cargoes from fish farms.
Hazards when transporting biological liquid cargo
Fish silage that is conserved correctly should not be a hazard to the ship or crew. If the conservation is not done correctly, however, explosive and toxic gasses may form. A decomposition process of the silage may also start if the temperature is right in the tank. The consequences may be lethal.
The development of hazardous gases is not limited to fish silage and should be considered when carrying all types of liquid cargo from a fish farm or fish-processing plant.
If the gas is exposed to heat from welding, cutting torches or angle grinders, it can easily be ignited, and the tank will explode. If anyone enters a tank or other spaces where gas may gather, they could be poisoned and die.
Several reported incidents indicated a lack of information about the cargo from the shipper. Some pieces of information that tend to be missing include the correct IMO hazard class, a description of the contents of the cargo and confirmation that the cargo is stable. This could lead to the master accepting cargo that the crew and ship are not equipped or certified to carry.
Hot work
– Always carry out a risk assessment when planning and carrying out hot work.
– Keep an overview of the cargo on board and any relevant hazards, such as the formation of gas.
– Make sure that the work area is safe considering sparks, the location of cargo tanks, etc.
Correct information about liquid biological cargo
– The shipper must provide the master with correct information on the contents and qualities of the cargo. Some of the factors to be documented include
– the correct product name for carriage in bulk
– that the cargo is stable
– any conditions for the cargo to remain stable
– dangerous situations that may occur if the cargo becomes unstable, etc.
– The product name must be listed in chapters 17 or 18 of the IBC Code or in MEPC.2/Circular. Before the cargo is taken on board, the master must ensure that this information is received an that the vessel is certified to carry a cargo with the product name listed in the shipper’s documentation.
Work in tanks
When employees plan to work in a tank that may contain silage remains, it is important to ensure that the atmosphere in the tank is safe before commencing the work.
– Always carry out a risk assessment when planning and carrying out work in tanks.
– Keep an overview of the hazards related to the cargo, especially gas formation hazards.
– Check and conduct necessary measurements to ensure a safe atmosphere in the tank.
– Use the information from the shipper to gather information about the cargo, keeping in mind the temperature and how long the remains from the biological cargo have been in the tank.
This must be included in the company’s safety management system, updated on a regular basis and documented.
