Fuel oil in tanks bordering cargo holds release excessive heat that can damage bulk and bagged agricultural products.
What Can Happen?
When the fuel oil is heated, the temperature of the tank plating rises and affects the adjacent cargo, possibly causing deterioration. In the case of seed cake or other agricultural products which are liable to self-heat, any hot surface, even an un-insulated engine room bulkhead, may promote self-heating. Hot fuel oil in double bottom tanks has caused cargo damage. The extent of the damage may extend several metres high. The holds affected are usually towards the stern where double bottom fuel tanks are typically situated.
What can Happen to the Cargo?
Due to such high temperatures, agricultural products may undergo:
- Discolouration or blackening of cargo
- moisture migration
- caking
- the formation of mould and malodour
- If a seed cake cargo also contains an excessive proportion of unoxidised oil or moisture, self-heating may ultimately result in spontaneous ignition
- During discharge a layer of heat damaged cargo will mingle with sound cargo spoiling it completely.
- Some ports may prohibit the discharge of damaged or rejected cargo, requiring the vessel to proceed elsewhere to dispose of the distressed product thereby incurring additional costs and delays.
Factors which Impact the Magnitude of damage:
The intensity of damage depends on the following reasons:
- Temperature of the fuel oil
- The length of time that the product has been exposed to hot tanks
- The properties of the commodity concerned
Recommendations to avoid overheating of cargo:
- The engineers should be advised of the precise nature of the product and the proposed stowage plan well in advance of loading so that a suitable fuel oil management strategy can be adopted to minimise the risk of heat damage to the cargo.
- The IMSBC Code schedule for the cargo should be consulted for any particular requirements regarding stowage in way of heated fuel tanks and engine room bulkheads which are not insulated.
- Where possible, heated fuel tanks which do not border the cargo holds should be used.
- If it is necessary to heat a fuel tank which is in direct contact with the cargo, the oil should be heated to the minimum extent necessary to allow safe transfer. Excessive heating of fuel oil and fuel residues should be avoided. Similarly, hot oil should not be transferred into fuel tanks bordering the cargo holds.
- As far as practicable only the fuel tanks in use should be heated. In a recent case a double bottom tank containing fuel oil that was not being used was inadvertently heated to a high temperature for the entire voyage. Over 600 tonnes of heat damaged soybeans mixed with sound cargo was subsequently rejected by cargo interests.
- Should the cargo deteriorate on passage due to inherent vice, cargo interests may allege that the damage was caused by excessively hot fuel tanks. Consequently, detailed records of which fuel oil and fuel residue tanks were heated and the temperature of the oil they contain should be maintained throughout the voyage.
- Fuel oil heating arrangements, including temperature sensors in the tanks, should be included in the vessel’s planned maintenance system and undergo regular checks and tests.
Source: West of England P&I
