Information for Customers » Advices to Shippers for the Proper Carriage of Reefer Cargoes

General

Key issue is to mantain suitable storage conditions during transportation. This is a must for all type of commodities, being a critical issue when it comes to reefer cargoes.

Perishables include both frozen and chilled goods, the latter including fresh fruits and vegetables. Normally, frozen goods do not suffer if over-cooled, whereas chilled goods can be damaged by low temperatures, either by freezing or by chilling injury to fresh produce. Much tropical and sub-tropical produce is liable to chilling injury if subjected to temperatures below those usually experienced in the growing area.

Carriage instructions are paramount. These define the conditions in which the goods are to be carried. If these instructions are incomplete, inadequate, contradictory, or wrong, then problems can be expected. For the shipper, there is the risk of cargo loss. For the carrier, there is the risk of a claim even if the goods arrive soundly at destination.

Key Requirements

Shippers are responsable for specifying carriage instructions, being the owners of the goods. Only the shipper knows the full nature of the goods and their requirements. Frequently this responsibility is passed to the carrier, but in this case the shipper prior to shipment should agree the acceptability of the specified conditions. 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, growing season conditions and origin.

In case of mixed loads of differrent commodities 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 frequently an international journey may use different carriers at the start and end of the trip.

Relative humidity and maximum time without refrigeration are points thta should not be over-specified but should meet the necessary requirements of the goods. Over-specification of requirements is to be avoided as it tends to lead to more, and sometimes spurious, claims regarding technicalities which have not actually affected cargo quality or main characteristics.

Containerised Cargoes

Necessary items to be included in carriage instructions for containerised refrigerated cargo:

  • Pre-stuffing sanitation.
  • Cooling during part loaded conditions.
  • Stowage requirements.
  • Carriage temperature.
  • Air circulation rate.
  • Measurement and reporting requirements.
  • Need to pass instructions to subsequent carrier.
  • Pre-cooling of containers.
  • Prohibition of stuffing cargo at mixed temperatures.
  • Ventilation.
  • Maximun time without refrigeration.
  • Relative humidity.
  • Special conditions for cold weather.
  • Need to notify if limits exceeded.

For controlled atmosphere shipments, additionally:

  • Levels (ranges) for O2, CO2, humidity, ethylene.
  • Permitted time to reach specified levels.
  • Procedure in event of CA system failure.
  • Safety requirements.
  • Discharge atmosphere requirements.

Pre-stuffing sanitation. The proper cleanliness and lack of odour in containers to be used for refrigerated goods should be a matter of normal good practice, but any special or particular needs should be identified.

Pre-cooling of containers. Pre-cooling is only useful when loading from temperature controlled loading bays; in other conditions, it can result in excessive moisture ingress from the atmosphere and is not recommended.

Cooling during part loaded conditions. Part loaded containers should be closed and temperature maintained if there is a delay before completing loading.

Prohibition of stuffing cargo at mixed temperatures. Properly pre-cooled cargo and substantially warmer cargo should not be mixed.

Stowage requirements. Any special stowage requirements, such as a protected or underdeck stow, should be stated.

Ventilation. The rate of fresh air ventilation for fresh produce should be specified. This should be as an absolute figure in cubic metres per hour. The specification of a percentage rate of ventilation only has meaning if related to a specific container size and a specific model of refrigeration unit.

Carriage temperature. It is not physically possible to provide refrigeration in the absence of temperature differences, both between air and goods and within the bulk of the goods. The only temperature which can be controlled is the set point, which corresponds to air delivery temperature for chilled goods and to air return temperature for frozen goods. The term "carriage temperature" therefore has little meaning, and "set point temperature" should be specified. If appropriate, this may be augmented by a maximum allowable temperature during periods without refrigeration.
Although degrees Celsius are the international standard, in the USA degrees Fahrenheit are still commonly used. As zero C is a common chilled goods temperature and zero F is a common frozen goods temperature, great care is needed to avoid possible confusion of units.
For USDA and other cold treatment quarantine requirements, maximum pulp temperature may have to be maintained below a specified temperature throughout a continuous period of days or weeks, and only approved equipment may be used.

Maximum time without refrigeration. Sometimes it may be necessary for statutory or other reasons to specify a maximum duration of time without refrigeration, either per event or in total for the journey. This should not be necessary if temperature limits are well defined.

Air circulation. Many containers have a high air circulation rate for chilled goods and a lower rate for frozen goods. If a speed change switch is fitted, low speed operation for chilled goods may be possible, but as this inevitably results in a wider range of cargo temperature, it is not recommended.

Relative humidity. When special equipment with humidity control is used, a range must be specified. It is difficult to measure humidity regularly to better than the nearest 2 to 3%, so an acceptable range of at least plus or minus 5% should be specified, albeit with a tighter target. Special equipment is available to maintain either high (e.g. 90%) or low (e.g.50%) humidity. Without such equipment, relative humidity is not controllable and should not be specified.

Measurement and reporting requirements. It is normal to record return air temperature in refrigerated containers, and some equipment also records delivery air temperatures. Any specific shipper requirement for reporting temperatures should be stated. When the refrigeration unit is not running, the recorded temperatures do not reflect cargo temperatures. Shippers may choose to put their own recording equipment within cargo, in which case they should inform both carriers and receivers.

Special conditions for cold weather. Sometimes special requirements exist for exceptionally cold conditions. However, it should be noted that most transport refrigeration equipment will control temperature using either cooling or heating as necessary to maintain specified conditions.

Need to pass instructions to subsequent carrier. If there is uncertainty at the start of a voyage as to who will be the final carrier, it may be necessary to request the initial carrier to pass on carriage instructions.

Need to notify if limits exceeded. Procedures for notification of out of specification conditions should be established prior to acceptance of cargo for shipment. This could apply to warm loading, or to equipment failures, for example. Standard procedures and safe limits should be available.

Additional requirements for Controlled Atmosphere shipments. Controlled Atmosphere (CA) systems are designed to maintain an atmosphere different from normal, usually with low oxygen and increased carbon dioxide. They enhance the storage life of some produce when used in conjunction with refrigeration. There are additional requirements for such shipments, as follows:

  • Levels (ranges) for O2, CO2, humidity, ethylene. For each of the atmospheric gases to be controlled, upper and lower concentration limits should be specified.
  • Permitted time to reach specified levels. The maximum time allowed to reach the specified levels may be laid down.
  • Procedure in event of CA system failure. The failure of a CA system will not necessarily have a drastic effect on the produce if the refrigeration continues to run. In these circumstances it will be necessary to introduce fresh air ventilation to fruit and vegetable cargoes. This should be specified.
  • Safety requirements. CA produces an atmosphere which is deadly to humans - breathing an oxygen-depleted atmosphere produces immediate unconsciousness and fairly rapid death. Adequate safety systems must be in place, and these may need to allow for the possibility of stowaways in the cargo.
  • Discharge atmosphere requirements. The safety requirements extend to those unloading cargoes. Proper ventilation prior to entering containers and training of workers are both necessary.