Any cargo that has to be loaded, maintained and/or carried at a certain temperature in order for it to reach its destination without deterioration is classed as refrigerated cargoes.
This includes meat, fish, poultry products, dairy products, drugs and experimental samples. Refrigerated cargoes are perishable to a greater or lesser degree, and their safe carriage depends on maintaining suitable storage conditions during transportation.
Types of Refrigerated Cargoes
- Goods carried in frozen state i.e. meats, fish and butter
- Goods carried in chilled state i.e. beef, vegetables, cheese and eggs
- Goods carried in air cooled condition i.e. fruits
Note: Drugs and experimental samples may be frozen or chilled.
Properties of Refrigerated Cargoes
- Rapid deterioration if proper temperatures are not maintained during loading, voyage and discharging.
- Susceptible to tainting and moisture contact damage.
- Effected by presence of CO2.
General Requirements for Safe Transport
The responsibility for specifying carriage instructions is that of the shipper/owner of the goods. Only the shipper knows the full nature of the goods, their prior history and their requirements.
Frequently this responsibility is passed to the carrier, but in this case the shipper should agree the acceptability of the specified conditions prior to shipment.
In either case, the exact nature of the cargo needs to be known – in the case of fruit, for example, carriage requirements may vary dependent on type, variety, maturity, origin and growing season conditions.
Some of the general carriage requirements are:
- Segregation of cargo - If mixed loads of differing commodities are to be carried in a single cargo space, it is necessary to consider compatibility of temperature, atmosphere (especially ethylene levels) and liability to taint. This will usually require specialist cargo care advice.
- It may be necessary to ensure that carriage conditions are specified to all carriers in the transport chain, as on occasions an international journey may use different carriers at the start and end of the journey.
- Items such as relative humidity and maximum time without refrigeration should not be over specified but should meet the necessary requirements of the goods.
- Efficient refrigeration machinery and good insulation of the compartment.
- Careful preparation of the compartment including cleaning, dunnaging and pre-cooling.
- Effective system for monitoring and maintaining specified temperature during loading, transportation and discharging.
- Monitoring and control of CO2 concentration in the compartment, and good ventilation.
Specific requirements for reefer ships
The parameters that may be included in carriage instructions for refrigerated cargo are listed below:
- Pre-loading sanitation.
- Pre-cooling of cargo space.
- Cooling during part-loaded conditions.
- Prohibition of loading cargo at mixed temperatures.
- Stowage requirements.
- Ventilation (or lack of) during cooling.
- Ventilation thereafter.
- Carriage temperature.
- Air circulation rate.
- Relative humidity limits or targets.
- Carbon dioxide limits or targets.
- Ethylene limits.
- Measurement and reporting requirements.
- Special conditions for cold weather.
- Need to pass instructions to subsequent carrier.
- Need to notify if limits exceeded.
For controlled atmosphere shipments, additionally:
- Levels (ranges) for O2, and CO2, humidity, ethylene.
- Permitted time to reach specified levels.
- Procedure in event of CA system failure.
Preparation of Compartment
The proper cleanliness and lack of odour in compartments to be used for refrigerated goods should be a matter of normal good practice, but any special or particular needs should be identified.
It is desirable that holds are allowed to warm to ambient temperature before cleaning begins. The odours of residue from previous cargo are then more readily detectable and are not masked by the residue remaining in frozen state. In the above case detection of the putrefaction was delayed by the gradual rise in the temperature from hard frozen to chilled.
Pre-cooling of cargo space
- To allow for temp fluctuations during loading
- To ensure carriage temp achieved ASAP
- Begins once holds are clean & dry
- Dunnage cooled at the same time
- May take 24 - 48 hours
Certification for cleanliness and pre-cooling required from cargo super or terminal.
Approximate pre-cooling temperatures: -
- Frozen compartments 10oF
- Chilled compartments 22oF
- Apples, pears, peaches and grapes 28oF
- Oranges, lemon, grape fruit 36oF
- Cheese 40oF
The pre-cooled compartment should be inspected by the appointed surveyor and certified ‘fit to load’ before loading can commence.
Ventilation (or lack of) during cooling
For most refrigerated cargoes, the cargo should be loaded at the required carriage temperature. For some cargoes, notably bananas and the less sensitive citrus varieties, cooling in transit is normal. In these cases a period of 48 hours should be specified, during which fresh air ventilation is stopped to allow maximum refrigeration.
After cooling, or throughout in the absence of cooling, the rate of fresh air ventilation for fresh produce should be specified. This may be as an absolute figure in cubic metres per hour, or as a rate in air changes per hour of the empty volume of cargo space. Alternatively it may be linked to measured values of humidity, ethylene or carbon dioxide. Care is necessary to avoid requirements that conflict.
- Sweep and clean thoroughly with particular attention to brine pipes, insulation, bins, gratings, air ducts in order to remove all traces, stains and odour of previous cargo. After cleaning these should be wiped down with a disinfectant fluid to prevent formation of mould there on.
- Bilges should be made dry, cleaned and ventilated in order to remove foreign matter and odour. Brine traps are provided to seal the drain pipe from tween decks to bilges in order to allow only one drain passage from tween deck to bilges and stop any back flow of gases/ foul odours from bilges to cargo space. These should be checked and topped up to prevent cold air from entering the bilges and freezing them or odour from reaching the refrigerated compartment.
- Strum boxes should be cleared and bilge suction tested.
- Clean dunnage, likely to be used, meat hooks, bars chains or any other equipment or appliances to be used for loading or stowage of cargo should be placed in the compartment after they have been cleaned and sterilised.
- Thermometers should be tested and kept ready and thermometer pipes, if removed, should be fitted, or extended to enable recording of temperatures at the top, middle and lower levels of the compartments.
- Portable trunks in holds of battery compartments must be assembled in place.
Loading, Discharging, Handling Refrigerated Cargoes
1. Cargo tendered for shipment should be inspected thoroughly: -
a) Frozen cargo should be hard frozen and free of spots or mould. There should be no blood stains on the wrappings.
b) Fruit should not be in advanced stated of ripeness, skin should not be discoloured and should not be brown on the inside. Random samples should be taken and cut open.
2. Cooling in compartment opened for loading should be stopped to prevent frosting of grid pipes which will not only reduce cooling efficiency but on melting will result in water accumulation in the compartment and possible damage to cargo there in. Any snow formation on pipes should be carefully swept off.
3. Compartments not being worked should be kept closed. If necessary to keep them open to permit loading in adjoining hold or space escape of cold air should be prevented by rigging tarpaulin screens or some similar device. Air screens may be fitted on some ships.
4. Monitor temperature in the compartment during loading and should it rise above the specified level, close the compartment and re-cool it.
5. No walling should be permitted on cases of fruit, eggs or cheese as they are fragile Over other frozen cargo, shoes should be covered with clean gunny sacking or similar material.
6. Cargo should not be dragged, pushed or thrown. Slings should be made in the hatch square.
7. Proper cargo gear should be used e.g. canvas nets for meat and trays for crates/cases of cheese, butter, eggs and fruit.
8. Heavy meat should not be stowed over light meat.
9. Taintable cargo should not be stowed with fruit nor loaded in a compartment which has carried fruit unless it has been de-odourised.
10. Thick paper should be pasted over joints to prevent air leak.
11. Dunnaging is carried out in hold to prevent cargo movement and to prevent "short-cycling". (Short Cycling is the airflow choosing the path of least resistance, ie; around rather than through the cargo.)
Dunnaging should be so arranged so as to
a) provide adequate support to the cargo,
b) ensure sufficient clearance from deck and sides to prevent contact between cargo and the cooling pipes, air ducts, baffle plates and any water likely to condense in the compartment.
c) In the event of different temperatures being maintained in adjoining compartments liberal use should be made of saw dust on deck dunnage on the sides and drip trays under deck head to prevent water contamination in the warmer compartment,
d) to prevent damage to bottom tiers by over stowed cargo,
e) to permit unobstructed circulation of cooled air below, around and through the cargo including dunnaging at intermediate tiers for cargo of tight block stow type so that uniform temperature can be maintained throughout the compartment.
Principal refrigerated cargoes and respective carriage temperatures
Frozen beef About - 10oC (1oF).
Frozen lamb/or mutton From about - 8oC to - 10oC (15o to 18oF).
Frozen pork About - 10oC (15oF).
Packed in cases and carried at - 10oC to - 12oC (10-15oF).
Butter Liable to taint and should not be stowed alongside other strong smelling cargoes in the same compartment, e.g. fruit. Generally packed in cartons. Carriage temperature about - 10oC (15oF).
Cheese Carriage temperature varies but generally carried at 5–7oC average. Usually stowed on double dunnage
Shipped in boxes or crates and should be stowed on 50-mm dunnage. Fish has a tendency to rapid deterioration, and should be carried at a low a temperature as possible, which should not exceed - 12oC (10oF).
Fruits & Vegetables
- Apples Carriage temperature will vary with the variety of apple but is usually in the range of - 1–2oC.
- Pears Should not be stowed in the same compartment as apples. Carriage temperature -1oC to 0oC (30–32oF).
- Grapes, peaches, plums Carriage temperature - 1oC to 2oC (31–35oF).
- Oranges must have adequate ventilation as they are very strong smelling and the compartment must be deodorized after carriage. Carrying temperature 2–5oC (36–41oF)
- Lemons Similar to oranges. Carrying temperature 5–7oC (41–45oF).
- Grapefruits Similar stow to oranges. Carriage at about 6oC (44oF).
- Banana trade is specialized and special ships are built for the purpose. Many of which use containers. The carriage temperature is critical as too low a temperature can permanently arrest the ripening process. Daily inspection of a compartment would be carried out and any fruit found to be ripe is removed. One ripe banana in a compartment can cause an acceleration of the ripening process throughout the compartment. Carriage temperature usually about 12oC (52–54oF).