Reefer Containers: Meaning, Temperature Ranges and ATP

Reefer containers are refrigerated shipping containers: insulated boxes with their own refrigeration unit that hold perishable cargo at a set temperature, chilled or frozen, from loading to delivery. "Reefer" is short for refrigerated, and in road freight the word has a second meaning: the reefer trailer, a refrigerated semi-trailer with the cooling unit on its front wall. Both carry food, flowers and pharmaceuticals, and both are planned around one number, the set point.

How a reefer works

The refrigeration unit blows cooled air around the load and holds the temperature the shipper has set. For fruit and vegetables, which keep breathing after harvest, it can also let in fresh air, and some units control humidity or the oxygen and carbon dioxide in the box (controlled atmosphere). The controller records temperatures and settings throughout the trip.

• A reefer holds temperature, it does not pull down a warm load. Chilled goods are pre-cooled and frozen goods pre-frozen before loading; a set point below the carrying temperature does not cool faster and can damage the cargo.
• Air has to flow. Never stow above the red load line inside a reefer container, keep pallets stable and evenly spread, and close the fresh-air vent for frozen cargo.
• Power never stops. At terminals and on ships the container is plugged in; on the road a diesel generator set (genset) travels with it, while a reefer trailer runs its own unit.

Reefer containers and reefer trailers

A reefer container is an ISO container for intermodal transport: shipping lines run 20-foot and 40-foot high cube reefers by ship, rail and truck. On the road it rides on a container chassis, which turns the combination into an articulated truck, with the weight limits that apply to it, just like the other standard container types and sizes that move by road. Container, cargo, chassis and genset together must stay within the weight limits of every country on the route.

A reefer trailer is a refrigerated semi-trailer with the unit on the front wall, loaded with pallets at a temperature-controlled dock. Multi-temperature trailers split the body into compartments with their own set points, so chilled and frozen goods share one tour. In road freight, "reefer" usually means the trailer.

Temperature ranges and ATP classes

Standard reefer containers hold set points from about -30 °C to +30 °C (the range Maersk lists for its 20-foot and 40-foot high cube standard reefers), and super-freezers reach -60 °C. Within those temperature ranges, the cargo decides:

• Frozen: quick-frozen food in the EU must stay at -18 °C or colder at every point of the product, with brief rises of no more than 3 °C allowed during transport (Directive 89/108/EEC).
• Chilled: meat, poultry, fish and dairy travel chilled, at the maximum temperatures the ATP agreement sets per product. For fresh produce and medicines, the shipper's instructions decide.

The ATP agreement sorts mechanically refrigerated equipment into classes by the inside temperature the unit can reach and hold when it is +30 °C outside:

ATP: the agreement for perishable foodstuffs

The ATP (Agreement on the International Carriage of Perishable Foodstuffs and on the Special Equipment to be Used for such Carriage) was signed in Geneva on 1 September 1970 under the UN Economic Commission for Europe. It applies to international carriage of these foods to or from its contracting parties (50 countries, according to the UK government) and covers frozen food and chilled products such as meat, fish and dairy, but not fresh fruit and vegetables.

The equipment is tested and certified, with a first certificate valid for up to six years and further tests after that. On international journeys the certificate travels in the vehicle or a certification plate is fixed to the equipment, and the class mark (FRC for a heavily insulated class C unit, for example) and the expiry date appear on both sides near the front. Domestic runs follow national rules.

What a dispatcher plans differently

• The set point belongs to the order. Get the carrying temperature and the ventilation setting in writing with the booking and pass them to the driver.
• Check the load, not only the unit. Goods must be at carrying temperature when loaded; note deviations on the consignment note and, on international loads, check the trailer's ATP mark.
• Time costs more. The unit runs while the truck waits, so waiting and cleaning belong in the price. A truck cost calculator that prices a tour per kilometre and per hour shows what an hour at the dock is worth.
• Records travel with the load. Quick-frozen food needs temperature recorders to EN 12830, with records kept for at least one year (a visible thermometer suffices in local distribution).
• Slots are tight. Plan the unloading point's ramp, equipment and time window before the truck leaves: a refused load means a trip back.