temperature maintained if there is a delay before completing loading.


Prohibition of stuffing cargo at mixed temperatures


Properly pre-cooled cargo and 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


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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


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