Reefer Container Operations: An Ops Team's Guide

The claim arrives three weeks after delivery. Forty thousand kilos of frozen fish arrived at 12 degrees below zero instead of 18 below, the consignee rejected the lot, and now everyone wants to know who moved the set point. You pull the file. The booking says minus 18. The shipping instruction says minus 18. Nobody ever downloaded the unit’s temperature record, and the reefer went back into service eleven days ago.

A reefer container is the only piece of equipment in ocean freight that can quietly destroy the cargo inside it while every milestone in your system shows green. The box arrived. The container was discharged. The delivery was completed. None of those events say anything about what happened to the air inside.

The FAO and UNEP found that 12% of all food produced globally, around 526 million tonnes, is lost because of insufficient refrigeration, with losses in the transport leg alone reaching 20% to 25% where temperature fluctuates or distribution stalls.

How a Reefer Container Actually Works

Most reefer problems trace back to one misunderstanding: people assume a refrigerated container is a freezer. It’s a climate maintenance system, and the difference shows up on every shipment you handle.

A reefer unit pulls air from the cargo space, passes it over an evaporator coil, and blows conditioned air back in under the floor. That air travels up through and around the cargo and returns to the unit at the top. The machine controls a moving stream of air. It doesn’t reach into a pallet of mangoes and pull heat out of the fruit.

This is why cargo must arrive at temperature. A reefer can hold 20 tonnes of frozen product at minus 18 for six weeks. It cannot take that same product from minus 5 down to minus 18 in any reasonable time, and trying will cost you the cargo.

Set point, supply air, and return air

Three temperatures matter, and confusing them causes disputes.

Set point is what you instruct the carrier to run. It goes on the booking, the shipping instruction, and the B/L.
Supply air (also called delivery air) is the temperature of the air leaving the unit and entering the cargo space.
Return air is the temperature of the air coming back to the unit after passing through the cargo.

Carriers control on one or the other depending on the cargo. Chilled cargo is normally controlled on supply air, because fresh produce sits in a narrow band and a couple of degrees of drift causes chill damage. Frozen cargo is normally controlled on return air, because the product is already stable and what matters is the warmest point in the load.

When a claim gets technical, this is where it lands. A return air reading of minus 16 on a frozen load doesn’t automatically mean the cargo breached minus 18. Knowing which sensor the carrier controlled on tells you whether you have a real excursion or a misread number.

Airflow, the T-floor, and the red load line

The floor of a reefer is T-shaped aluminium decking, and the channels it creates let air run the length of the container underneath the cargo. Block those channels and the air takes the shortest path back to the unit instead of through the load.

Two loading rules follow, and shippers break both constantly:

Never stack above the red load line. That marking near the ceiling exists so return air has a clear path back to the intake. Cargo stacked to the roof chokes the circuit and the far end of the container never gets conditioned air.
Frozen cargo is block stowed, chilled cargo is not. Frozen product should be loaded tight and solid so air passes around the block. Respiring cargo like fruit and vegetables needs air moving through it, which means spacing, vented cartons, and aligned vent holes.

In our experience, the usual physical cause of a reefer claim is a container loaded by someone who treated it like a dry box.

Fresh air exchange and controlled atmosphere

Living cargo keeps breathing after you close the doors. Fruit and vegetables consume oxygen, give off carbon dioxide, and release ethylene, which accelerates ripening. The fresh air exchange vent lets you swap a set volume of air per hour to bleed off CO2 and ethylene.

The vent setting is cargo specific and belongs in your shipping instruction rather than in the driver’s judgment. Frozen cargo ships with vents fully closed. Opening vents on a frozen load pulls warm humid air into the box and builds ice on the coil.

Controlled atmosphere goes further. CA units manage oxygen and carbon dioxide levels, usually by injecting nitrogen, to hold produce in a dormant state for long transits. Bananas, avocados, and blueberries on long-haul trades often move this way. CA equipment is scarce and carrier specific, so request it and get it confirmed at booking.

Where Reefer Shipments Actually Go Wrong

Reefer failures cluster in a few places, and once you know them most are preventable with a phone call.

TT Club, the transport insurance mutual, reports that temperature-controlled cargo ranks third among all claims in its book, and that roughly a third of those losses trace to communication and clerical errors, including Celsius and Fahrenheit mix-ups, with a further 23% caused by incorrect temperature settings. Equipment failure accounts for about a quarter. Usually it’s the instructions that break, not the machinery.

The set point was never confirmed in writing. The shipper’s email says “minus 18 Celsius.” The booking gets keyed as minus 18. Somewhere between the carrier’s booking desk and the terminal, the unit is set to minus 1.8 or plus 18. Decimal points and missing minus signs sink real shipments.

Cargo was stuffed warm. The shipper loads product straight off a production line or an ambient warehouse and expects the container to pull it down. The unit runs at full capacity for days, never reaches set point, and the data record shows a container that “never worked.”

The container was pre-cooled when it shouldn’t have been. If you’re stuffing at an ambient dock, pre-cooling the empty container is usually a mistake. Warm humid air hits cold surfaces, condensation forms on the floor and coil, and you start the voyage with water and ice in the box. Pre-cool the container only when loading through a sealed cold dock. Otherwise, cool the cargo and run the unit after the doors close.

Power gaps nobody logged. A reefer needs continuous power. It gets unplugged for the terminal gate move, plugged in at the yard, unplugged for loading, plugged into the vessel, and the same again at discharge and on the road. Short gaps are normal and harmless. Long ones aren’t, and they rarely appear in any system you can see.

The unit was never PTI’d, or the PTI was old. A Pre-Trip Inspection is the carrier’s automated self test of the unit before the box is released. It checks the compressor, sensors, defrost cycle, and airflow. A container released without a recent passing PTI is a gamble you took on the shipper’s behalf.

The doors were opened in transit. Customs inspection, a stuffing correction, a partial delivery. Each door opening dumps the conditioned air and shows up as a spike in the record. If your file doesn’t explain the spike, the carrier will use it to explain the claim.

The Pre-Shipment Checks That Prevent Most Reefer Claims

Reefer work rewards pedantry before departure. Everything below happens before the vessel sails.

Get the set point, vent setting, and humidity requirement in writing from the shipper. An email or an instruction form with the units spelled out: “minus 18 degrees Celsius, vents closed.” A phone call won’t do, because ambiguity here is unrecoverable later.
Repeat those values back on the booking and check the carrier’s confirmation. Read the confirmed set point as a separate act from reading the vessel and voyage. Ops teams that skim the confirmation catch schedule errors and miss temperature errors.
Request the PTI report or at least the PTI date. Most carriers will provide it, and it’s a normal request. If the unit hasn’t been PTI’d recently, ask for a different box.
Confirm the cargo is at temperature before stuffing. Ask the shipper to record pulp temperatures at loading. For high value or claim-prone commodities, this should be a condition of the booking.
Put an independent data logger inside the cargo. The unit records its own air temperatures; a logger sitting in the product records what the product experienced. On any shipment where a claim would hurt, it pays for itself the first time you use it.
Photograph the load and the load line. A picture of a properly stowed container with the red load line visible ends most arguments about whether the cargo was stacked too high.

The wider workflow is in our freight booking management guide. The reefer difference is that a keying error doesn’t just delay a box. It ruins what’s in it.

What Happens to a Reefer During Transshipment and Port Delays?

Delay is more dangerous for reefer cargo than for anything else you move. A reefer sitting in a yard consumes free time, draws power, and burns shelf life at once.

Sea-Intelligence reported global schedule reliability of 59.0% in February 2026, with the average delay for late vessel arrivals reaching 5.49 days. For a dry container, five and a half days is a frustrated customer. For a chilled load with a 28 day shelf life sold on arrival condition, it can be most of the commercial margin.

Blank sailings compound it. Drewry’s cancelled sailings tracker recorded 46 blank sailings across a recent five week window, a 6% cancellation rate concentrated on the Transpacific and Asia to North Europe trades. A rolled reefer is not the same problem as a rolled dry box, because the cargo has a clock on it that the booking doesn’t.

Transshipment is the highest risk segment of any reefer routing. At a transshipment port the box is discharged, moved to a stack, plugged in, monitored by whoever the terminal assigns, and later loaded to a second vessel. Every one of those steps is handled by a party you have no contract with. We covered routing tradeoffs in our transshipment routing guide, and for reefer cargo a direct service at a higher rate frequently beats a transshipment routing at a lower one. On high value perishables the gap isn’t close.

Three things worth doing when delay is likely:

Ask the terminal for reefer monitoring records, not assurances. Terminals log plug-in status and temperature checks at defined intervals. Request the log, because “it was monitored” is not a record.
Know whether the destination has reefer plug capacity. Congested terminals run out of powered reefer slots before ground slots. When that happens, boxes wait unplugged.
Arrange gensets early for road moves. A reefer on a chassis needs a clip-on generator or a genset-equipped tractor. In a tight drayage market these run out first, a dynamic we covered in our drayage management guide.

Reefer Documentation Goes Beyond the Standard File

A dry shipment needs the commercial set. A reefer shipment needs that plus a temperature story that holds up months later.

Temperature records from the unit. Reefers record continuously through an onboard data recorder. That data is retrievable but not retained forever, and units go back into service and get overwritten. Download the record at delivery as routine, before any claim appears. We made this point in our freight claims filing guide, and it remains the most commonly missed step in reefer claims.

Cold treatment protocols. Some markets require in-transit cold treatment to kill fruit fly larvae, with the cargo held at a specified temperature for a specified number of consecutive days. This is a quarantine procedure with real paperwork: calibrated pulp probes placed to a defined pattern, sensor calibration certificates, and a treatment record that the destination authority reviews before release. Probes placed wrong will fail the shipment on arrival no matter how good the actual temperature control was.

Phytosanitary and health certificates. Perishables usually carry origin certification tied to the specific consignment. These are date sensitive and a delayed sailing can invalidate them.

Pharmaceutical requirements. Temperature-controlled pharma runs under Good Distribution Practice expectations, which means qualified lanes, documented excursion handling, and an audit trail your customer’s quality team can inspect. If you’re moving pharma with the same process you use for frozen protein, you have a gap.

The reefer and dangerous goods overlap. Some temperature-controlled cargo is also regulated as dangerous goods, and those products need both a controlled temperature and a DG declaration. The documentation requirements stack, as we set out in our dangerous goods ops guide.

Where Reefer Money Leaks

Reefer shipments carry cost exposures that don’t exist on dry cargo, and they are routinely under-quoted.

Plug-in and monitoring charges. Terminals bill for powered reefer slots by the day, separately from storage, and the charge often lands on a settlement nobody quoted for.
Shorter free time. Reefer free time is typically shorter than dry free time at the same terminal, and reefer demurrage rates are higher. A tariff you know well for dry boxes may look very different in the reefer column, a pressure we covered in our container free time guide.
Genset hire. Charged per day, per move, and sometimes with a minimum. Easy to forget at quoting time, impossible to avoid at execution.
Pre-cooling and cold storage at origin or destination. Especially when a vessel delay means the cargo has to go somewhere refrigerated.
The cargo itself. A single rejected reefer load can exceed a year of margin on the lane, which is why the pre-shipment checks above are worth the friction they cause.

If your quoting process treats a reefer as a dry container with a surcharge, these charges surface at settlement as unrecoverable cost. Our guide to demurrage and detention management covers how these charges accumulate and where recovery is possible.

Frequently Asked Questions

What is the difference between a reefer container and a dry container?

A reefer container is an insulated container fitted with an integrated refrigeration unit that maintains a set temperature by circulating conditioned air through the cargo space. A dry container is an uninsulated steel box with no temperature control. Reefers require continuous electrical power from a terminal plug, vessel socket, or generator, and they carry a specific loading pattern that keeps airflow channels clear.

What is a reefer PTI and why does it matter?

A PTI, or Pre-Trip Inspection, is an automated self test the carrier runs on a refrigeration unit before releasing the container. It checks the compressor, temperature sensors, defrost cycle, airflow, and refrigerant charge. A recent passing PTI is your evidence that the unit was functional at handover. Requesting the PTI report or date before stuffing is standard practice on temperature-sensitive cargo.

Should you pre-cool a reefer container before loading?

Only when loading through a sealed cold dock. If you pre-cool an empty container and then stuff it at an ambient dock, warm humid air condenses on the cold floor and evaporator coil, putting water and ice into the container before the voyage starts. The correct approach in most cases is to load cargo that is already at temperature and start the unit once the doors are closed.

What temperature should a reefer container be set at?

The set point comes from the shipper’s cargo specification, never from a general rule. Frozen product typically runs at minus 18 degrees Celsius or colder, while chilled produce sits between zero and 15 degrees depending on the commodity. The set point, the vent setting, and any humidity requirement should be confirmed in writing by the shipper and repeated on the booking and the bill of lading.

Who is responsible when reefer cargo arrives at the wrong temperature?

Responsibility depends on where the failure occurred. Carriers are generally liable for maintaining the instructed set point while the container is in their custody, but they are not liable for cargo that was stuffed warm, loaded above the red load line, or shipped with the wrong instructions. The unit’s temperature record and the cargo’s pulp temperatures at loading usually determine which explanation the evidence supports.

How Tier2 Cargo Keeps Reefer Details Attached to the Shipment

Most reefer failures in this guide are information failures. The set point lived in an email, the PTI date lived with the carrier, the temperature record lived in the unit, and none of it lived with the shipment file where the ops team could see it.

Tier2 Cargo treats reefer parameters as shipment data rather than free text. Set point, vent setting, and equipment type are captured at quote and carry through booking, documentation, and settlement, so the value keyed at the start is the value that prints on the shipping instruction. Its AI document extraction reads booking confirmations and B/Ls and surfaces mismatches between what you instructed and what the carrier confirmed, which is where decimal point and missing minus sign errors hide.

The cost side works the same way. Reefer-specific charges like plug-in fees, genset hire, and the shorter free time windows that drive reefer demurrage are handled through the same fee rules and tiered demurrage logic as the rest of your cargo, so they land in the forecast at quote instead of surfacing at settlement. Milestone tracking gives you the timestamps that matter when a consignee disputes condition on arrival.

See how it handles temperature-controlled shipments or book a walkthrough with our team.

Pick your three highest value reefer lanes and check whether anyone downloaded the unit temperature record on the last shipment that moved on each. If not, that’s the gap to close first, because it decides every claim you file next year.