Guidance for Reefer Container Loading and Carriage

The complex nature of reefer transport itself dictates that the relevant recommendations cannot be applied to every contingency. Therefore, this guidance is worded in relatively broad terms. In summary, the goal of ensuring that cargo is carried in a safe and efficient manner avoids causing damage to quality.

To this end, all parties involved should be fully aware of the critical importance of maintaining the aforementioned set temperature values throughout the voyage. Also, please note that reefers are not designed to lower the temperature of warm cargoes, even if the cooling is very slow.

If a ship is carrying reefers, it is recommended to consider the proposals below and to take note of additional guidance concerning the operation, stowage and transport of such equipment.

Loading and Carriage Guidelines  

- Ships should be equipped with manufacturer's refrigeration spare parts, tools and maintenance manuals specific to the refrigeration equipment in question. These tools and facilities should be used by the ship's refrigerator when emergency repairs are required during the voyage. There are different types of refrigerated equipment, each with its own repair and maintenance characteristics.  

- When servicing containers stacked more than one level on deck, it is important to provide a safe maneuvering platform.  

- The refrigerant charge should be based on the type and number of refrigerated containers on board. 

- It is important to obtain a detailed description of all shipping conditions, including temperature, ventilation and humidity requirements, from the shipper prior to shipping. The International Cold Chain Technology (ICCT) recommendations for shipping conditions are available on the ICCT website.  

- If the container is loaded at the loading port yard, an inspector should be assigned to monitor the temperature of the shipment upon arrival and to note any deviations from the instructions. 

- Any special requirements of the charter for refrigerated transport, such as monitoring procedures, repair requirements, parties to be notified in the event of a breakdown, etc., should be strictly adhered to and appropriate instructions should be given to the ship in writing. 

 - The ship should contain a reefer operating manual that specifies the conditions of carriage of the reefer cargo, the problems that may occur and an outline of the problem solving procedures. If problems occur that are not covered in the manual, expert advice should be sought.  

- At the start of loading, the crew should reconfirm that the ship's electrical outlets are compatible with the reefer plugs and that there are enough for all loaded reefers. If necessary, a sufficient number of conversion plugs should be available.  

- In case a power outlet fails, a spare refrigerated extension cord should be provided.  

- When the reefer is plugged in, the plug and receptacle should be locked in place with a locking ring. It should be checked to ensure that the refrigerated outlet box is fully closed to prevent water from entering during the voyage.

- Once the reefer is loaded and the power is on, have an experienced crew member check to make sure that the reefer is operating and that the temperature is gradually reaching the set point. If the refrigeration unit does not operate, basic inspection measures should be taken. For example, the switch on the control panel or the main switch in the control panel may be off. If the container still does not operate properly after the ship's refrigeration officer has checked it, you will need to seek assistance from shore-based personnel. If the problem is still not resolved, the container will need to be returned to the yard. 

- Many refrigerated container cargo claims arise because of confusion between Fahrenheit and Celsius, and between positive and negative temperatures. Once the container is loaded onto the ship, care must be taken to ensure that the temperature is set correctly. Any discrepancies between the actual temperature setting and the cargo shipping instructions should be reported immediately. 

- Reefers should be inspected at intervals of no more than six hours during the voyage. Each time, record the time of the inspection and the supply and return air temperatures. Details of any problems encountered should be recorded in the appropriate log book. In addition, automatic logging allows the relevant signals to be transmitted via cable to a central point. The system should be checked regularly to avoid incorrect information. 

 

Refrigerated Cargo Loading Temperature 

The reefer is used to maintain the temperature of the cargo at the time of loading. Although the reefer may lower the temperature somewhat over time for cargoes above the specified temperature, this is not an essential function of the reefer.

If the temperature of the cargo exceeds the temperature setting required by the shipper, warming the cargo will cause the supply air temperature to rise sharply as the air passes over the cargo. The return air temperature will rise accordingly, making it impossible for the cooler to effectively reduce the temperature before it is recirculated into the supply air. In this case, the control panel may indicate that the supply air temperature is higher than the set temperature. The difference between the supply air temperature and the return air temperature will in most cases decrease as the air continues to circulate, with the air temperature being lower than the cargo temperature, reducing the cargo temperature towards the desired temperature level. The return air temperature will stop rising when the refrigeration unit starts to operate in standard mode. 

The example given earlier demonstrates a situation where a refrigerated cargo is loaded with a high temperature. The temperature of the cargo was around -5°C at the time of loading, and shortly after loading the outside of the cargo reached the set value of -18°C. However, the center of the loaded cargo did not reach the set temperature until three days later.  

If the container temperature is higher than the set temperature, the refrigeration unit will cool down the surface layer of the cargo relatively quickly within a few days, but the center of the cargo will take quite a long time to reach the desired temperature. Frozen shipments should not normally deviate from the set temperature value by more than 3°C (5°F). Frozen goods (except bananas) should not deviate more than 0.4°C (1°F). However, this does not mean that such deviations are acceptable, and shipments should be received and delivered at the set temperature as closely as possible. 

 

Temperature and Defrosting 

During the operation of the refrigeration unit, ice will form on the evaporator coil, depending on the set temperature, the temperature of the goods, the amount of fresh air in the ventilation unit and the humidity of the goods. The refrigeration unit periodically enters a defrost state, where a series of electric heaters generate heat or blow hot air into the evaporator coil. All fans are stopped at this time to prevent hot air from entering the cargo hold. However, due to the proximity of the return air temperature sensor to the refrigeration unit, such temperature increases may be recorded. Therefore, unless processed by the data logging software, temperature records will show periodic temperature increases consistent with the defrost interval. If the defrost period is brief, the hourly temperature readings may vary somewhat from the defrost period.

It should be noted that such an increase in temperature readings does not immediately affect the actual temperature of the goods and does not mean that the refrigeration unit is in an unstable condition. Electronic data logging usually shows defrost intervals and durations in addition to temperatures.  

As mentioned earlier, if the loading temperature exceeds the set temperature, the refrigeration unit will begin to automatically lower the temperature of the load to the required temperature level. If the load has thawed, the refrigeration unit will attempt to lower the load temperature but will continue to defrost frequently. In addition to the cargo setpoint and supply and return air temperatures, the temperature control system provides detailed information about system problems in the form of error codes. The container temperature recording system does not normally record cargo temperature, only air temperature, which can be recorded by a U.S. Department of Agriculture (USDA) detector installed to comply with USDA refrigerated handling procedures for fruit shipments. A data logger placed in the shipment by the shipper will also record the general temperature. 

When the refrigeration unit fails, the temperature display and data logging will show a gradual and steady increase in temperature until the ambient temperature is finally reached. Again, the sensors will only record the air temperature, not the cargo temperature. The cargo will be somewhat protected from the outside air temperature by the surrounding insulation.  

There are many other cases where air temperature records do not necessarily represent the actual temperature or condition of the cargo. These examples show that definitive conclusions cannot be drawn from air temperature records alone.

 

Types of Reefer Containers

The most common type of reefer container is the 40' long x 9' 6" high "High Cube" with a frame mounted integral reefer unit bolted to the front. This container is called "integrals" container. Sometimes also use 20-foot combination containers, such containers are generally 8 feet 6 inches high. Now there are also frameless refrigerated containers, refrigeration machine directly integrated in the front of the refrigeration equipment. This refrigerated equipment is called "integrated" container.  

Refrigerated containers are filled with insulating material made of polyurethane foam. Over time, the insulation will deteriorate and the insulation will weaken, which means that the older the container, the faster it will heat up in the event of a power failure, and the more power it will consume to operate.

 

PTI

Before handing over a reefer to the shipper, the carrier or its local agent should pre-screen it. This involves the operation and inspection of the reefer unit by a specialized technician, usually in the port area. Pre-inspection is usually a two-part process: a visual inspection of the structural integrity of the container and refrigeration unit, and a series of electronic checks by activating a pre-inspection button on the refrigerated equipment, which gives a pass or fail test result. A fail means that the unit is malfunctioning or parts need to be replaced and a qualified refrigeration technician needs to be involved accordingly. The pre-test is stored in the data log.  

After the container has been loaded, a further pre-inspection may be carried out. This check is called "short PTI" or "function check" and is done properly without any impact on the cargo. If loading is delayed, it is necessary to repeat the pre-check. The exact interval depends on the operating procedure, and should usually be repeated after an interval of 30 to 90 days.

In some cases, generator sets are used to provide independent electrical power to assist in the cold chain operation from the shipper's plant until the container is loaded.

There are three types of generator sets: 

- Permanent fixed units

- Top clip-on units

- under-slung clip-on units 

Before the container is shipped, a similar inspection should be performed on the generator unit. Their serial numbers should be recorded. The fuel should also be checked to ensure that the generator has sufficient fuel for the entire operation. Before a container is shipped, verify its temperature setting and select the correct temperature unit (°C/°F), especially for containers with digital display mode. 

Most refrigerated containers use electronic logging devices to record temperatures. In some cases, you may have the option of typing in "Start Trip" ("Go"). 

Older reefers may experience temperatures recorded on a circular card called a PARTLOW chart. This chart is rotated by a clockwork mechanism and the temperature is recorded on the chart by a stylus. The key is that the winding mechanism should be able to rotate sufficiently to insert the new card from the beginning and rotate it to a position where the stylus can record the temperature according to the correct time and date. The chart and thermostat device should be able to match the temperature units required by the shipper. All relevant shipping details should be recorded on the chart by the carrier's representative or agent.

Inspections should also be made to ensure that ventilation and humidity control are at the required level. If data logging probes are required under USDA refrigeration handling procedures, they should also be inspected by the carrier's representative or agent before and after installation and after pre-testing to verify that they are properly calibrated and can properly monitor the set temperature.  

If cargo is carried under artificially aerated storage (CA) conditions, the air controls should be properly set and the fresh air vents should be closed. In addition, instructions should be given on the steps to be taken in the event of air control failure, which should include opening the fresh air vents while closing the CA system. In tropical or subtropical regions, it is preferable to crate containers in a temperature-controlled environment, such as in a cold storage facility. Even if the container is packed in a general environment, the container should not be pre-cooled except in special cases, as this can lead to excessive condensation on the inner surface of the container. 

When the container door is opened, the refrigeration system should be turned off to avoid excessive moisture accumulation on the evaporator coils. 

 

Reefer Container Shipment/Transfer

If a refrigerated container is awaiting shipment or transshipment, it should be connected to a stationary power source ashore or to a separate generator set so that the refrigeration equipment can continue to operate for temperature control. 

A representative of the carrier or station operator should inspect the reefer system at least four times every 24 hours and issue a monitoring report on the entire process. This report should be given to the agent prior to the container being shipped. Temperature settings and temperature records should be reviewed. Each time a reefer is monitored, the entire exterior of the unit should be inspected. 

During this inspection, all seals, including the veterinary seal, should be thoroughly inspected by pulling and twisting. The number of seals should also be checked and recorded. If any problems are found, the owner and/or agent should be notified immediately so that remedial action can be taken to mitigate potential cargo damage if necessary. 

Temperature Logging 

The container data logger monitors the supply and return air temperatures of the refrigeration unit and stores this data in an electronic memory. The memory also records pre-test results and alarms, as well as a series of data exchanges with the controller and power unit. This data can be downloaded directly to a computer and then printed, stored or sent as an email attachment. 

If the data logger is capable of recording a "start trip" message, this should include the origin of the container and its destination. It should also be checked to make sure that the date and time information is accurate. The use of any portable loggers in the container should be noted in the cargo documentation. Portable loggers may be disposable or recyclable devices with bimetal sensors, or electronic storage loggers. The latter may contain a cargo probe attached to a lead sheet or have an integrated sensor inside.  

Container freight stations can be equipped with portable recorders to assist in shipment preparation. In this case, the portable recorder chart should be accurately prepared by the carrier's representative or agent. The location of the logger and the date and time of its activation should be documented on all relevant documents. Although it is common practice to place the portable logger in the top carton by the stack door, a better location is the air supply opening adjacent to the end of the cooler, since normally the carrier can only guarantee the air supply temperature.

 

Seals and Their Integrity 

During the operation of the container freight station, the seal of the carrier should be applied immediately after the completion of the boxing and the serial number should be recorded on the shipping documents. If the shipper is responsible for crating, it is usually unlikely that the carrier or its representative will seal the container before it is returned to the yard for shipment. Once the container is received, it should be sealed immediately and the details recorded again on all relevant documents. 

If a container is sealed, all details should be recorded and checked for signs of tampering on arrival at the yard. Only containers with seals intact at the time of unloading will be allowed to be imported into the EU, USA and Japan, thus confirming that the goods have not been replaced during transport. The integrity of all seals should be reconfirmed by the ship or local agent when berthing at an intermediate port and the corresponding details should be recorded on the appropriate documents. 

There are special EU import requirements for goods classified and labeled as "quick-frozen" which require that the goods be maintained at the proper temperature from the time of production prior to acceptance by the carrier. In such cases, the carrier should ensure that all previous temperature records are included in the accompanying documentation. 

 

Classification of Commodities

Generally, refrigerated shipments can be divided into two categories. 

- Refrigerated 

- Frozen 

Many refrigerated shipments (e.g., fruit) are considered "live" shipments because they can still breathe after picking and are susceptible to decay due to self-heating, precocity, drying (wilting and shriveling) and other conditions. However, this is not the case for other commodities such as frozen meats and cheeses. The minimum set temperature for fruit is usually no lower than -1.1°C (30°F).

In contrast, frozen shipments are generally considered "inert" and are typically shipped at -18°C (0°F) or lower. Since both refrigerated and frozen shipments are perishable, care must be taken to ensure that such shipments are delivered in optimal condition.

For refrigerated shipments, with limited exceptions (e.g., meat, chocolate, film, chemicals, dairy products, artificially aerated storage shipments), ventilation is normally kept open. Some shipments may require humidity control or large amounts of fresh air (e.g., bulbs and flowers). It should be noted that most refrigeration units are only capable of reducing humidity, and this depends on the amount of fresh air provided.

Artificially aerated storage shipments require the use of special purpose containers capable of replacing oxygen levels with nitrogen and carbon dioxide to extend the shelf life of harvested products. This method is applicable to many fruits, both nuclear and non-nuclear, but requires specialized knowledge to determine the most appropriate gas concentration levels.

Adequate space must be left around the pile to allow for air circulation

 

Load Accumulation 

For transporting refrigerated cargo, proper stowage in the container is extremely important. However, this is rarely under the control of the carrier. Carriers usually receive a sealed container "purportedly loaded" with a particular cargo. 

For refrigerated cargo, the cold air is circulated around the cargo to reduce temperature changes at the edges (e.g., sidewalls, bottom and roof). For refrigerated fresh (active) cargo (e.g., fruits, vegetables), allow gas flow to cover the entire stack to remove heat, carbon dioxide, ethylene (if present), moisture, and other residual gases. 

Loaded cargo should not exceed the red line inside the container. The area space should be kept empty at all times to allow undisturbed air flow to the front vents. The ideal stowage pattern is to allow free flow of air supply air while avoiding cargo movement. Sufficient space should also be left around the stack to allow free air circulation.  

The stowage requirements for frozen goods are relatively simple and should be loaded at a specific set temperature. Stacking can be done in piles. However, the boxes should not be tied together too tightly, and in addition space should be left between the cargo and the side walls so that heat at the edges of the boxes can be removed by air circulation. This is particularly important for the smooth inner panel of the container. Fresh air ventilation ducts should be kept closed when loading frozen cargo.  

Accumulated cargo should cover the entire bottom of the container, but should not protrude from the bottom "T" panel so that the door area can be cooled effectively and return air can flow efficiently. In larger containers where the volume of the cargo is less than the available space, the stowage height should remain the same across the stacks.  

Since the stowage in the container plays an important role in maintaining the quality and safety of the cargo during transportation, expert advice should be sought if there are any questions or concerns when accepting a booking. 

 

Cargo Inspection

Wherever feasible, the temperature of refrigerated fruits and vegetables and the central temperature of frozen cargo should be checked prior to crating. Fruits and vegetables should also be inspected for pre-refrigeration damage such as mold, wilting, dehydration, wilting, discoloration, soft spots, broken and peeled skin, abrasions, frostbite and odor. Frozen goods should also be inspected for dehydration, dryness, displacement, odor, black spots and color changes, as well as signs of thawing and refreezing due to increased temperatures. Cartons, pallets and other packaging should also be checked for good condition and ability to protect the cargo throughout the shipping process. 

If the refrigeration machinery breaks down or becomes unstable during the ship's voyage and cannot be repaired on board, the ship should notify the company's office or agent in the next port so that repairs can be arranged on arrival at that port. In such cases, an inspector should be assigned to examine the details of the failure and to assess the condition of the container contents.  

If the reefer suffers physical damage, an inspector should also be assigned to investigate the extent of the damage and ensure that measures are taken to reduce the potential loss of cargo. Unless otherwise provided in the terms of the contract of carriage embodied in the bill of lading, the carrier may be permitted to open the container seals to take measures to mitigate potential losses. The method of inspection depends on the type of cargo. In such cases, an inspector or expert should be appointed to supervise the operation.

From STU Supply Chain: Guidance for Reefer Container Loading and Carriage