A reefer container is an ISO-standard refrigerated shipping unit that maintains a controlled internal temperature throughout a sea voyage, rail transit, or port dwell. This article covers reefer technical specifications, cargo type requirements, USDA and EU phytosanitary compliance, vessel power supply systems, pre-trip inspection procedure, and how temperature excursions translate into cargo claims. It is written for chief officers, cargo superintendents, and marine surveyors working on container vessels.
What are the technical specifications of a reefer container?
A standard reefer container is an ISO 1496-2–compliant refrigerated unit available in 20-foot, 40-foot, and 40-foot high-cube configurations. Its integral refrigeration machine maintains cargo-space temperatures from −30°C to +30°C, operating on 380–460 V three-phase shore power or a clip-on diesel genset. Internal dimensions and payload differ by size.
20-foot and 40-foot reefer dimensions
The 20ft reefer (ISO type 22R1) has internal dimensions of approximately 5.44 m × 2.27 m × 2.24 m and a maximum cargo payload of 27,700 kg. The 40ft high-cube reefer (ISO type 45R1) provides internal dimensions of roughly 11.56 m × 2.27 m × 2.50 m, with a payload capacity near 29,000 kg. For a direct comparison of standard versus high-cube footprints, the 20ft vs 40ft shipping container dimensions guide covers both reefer and dry-box variants.
Refrigeration unit and airflow design
The refrigeration machine mounts in the front wall behind the compressor-condenser-evaporator assembly, drawing power from the ship or terminal. T-bar aluminium decking channels supply air under the cargo stack and return it across the top. Fresh-air ventilation dampers allow CO₂ and ethylene to be purged from the cargo space, an essential function for climacteric fruits.
Wall and ceiling insulation is typically 80–100 mm polyurethane foam, achieving a U-value below 0.4 W/m²K. The unit draws 3–6 kW at setpoint in steady-state conditions, rising to 10–15 kW during pull-down from ambient.
What cargo types are carried in reefer containers, and what are their temperature requirements?
Reefer containers carry three broad cargo categories — frozen, chilled, and controlled-atmosphere (CA) — each with distinct temperature, humidity, and airflow requirements. Mixing incompatible products in the same container, or even the same hold, can cause cross-contamination or accelerated ripening.
Frozen cargo
Frozen cargo — fish, shellfish, frozen meat, ice cream, and frozen ready meals — requires setpoints typically between −18°C and −25°C. The temperature of the cargo itself must reach −18°C or below before stuffing; pre-chilling a warm product in a reefer unit causes extended pull-down, risks setpoint deviation, and is a leading cause of out-turn temperature claims.
SOLAS Chapter VI Regulation 5 requires that cargo which deteriorates rapidly be carried under conditions appropriate to its nature. For frozen meat specifically, the IMO Model Course 3.14 for cargo care references ICMSF criteria requiring −18°C at the thermal centre as the minimum.
Chilled and fresh cargo
Chilled cargo — fresh fruit, vegetables, dairy, cut flowers, and pharmaceutical products — typically requires setpoints between 0°C and +15°C, with high relative humidity (85–95 %) to prevent desiccation. Banana carriage is commonly conducted at +13°C; avocados at +5°C to +7°C; chilled beef at −1.5°C to 0°C.
Humidity control matters because most reefer units return air across the evaporator coil, which removes moisture. Shippers of high-value horticultural produce sometimes specify desiccant-free stowage or limit defrost cycles to maintain relative humidity within the required band.
Controlled atmosphere (CA) cargo
CA reefers modify the gas composition inside the unit, reducing oxygen to 2–5 % and elevating CO₂ to 5–15 %, which suppresses the respiration rate of climacteric fruit and extends shelf life by four to six weeks beyond a standard reefer carry. Nitrogen flushing displaces oxygen to the target level after door closure.
CA-capable units require an airtight cargo space and real-time gas monitoring. Crew must treat an open CA container as a confined space: entry without a self-contained breathing apparatus (SCBA) in an atmosphere below 19.5 % oxygen is prohibited under SOLAS Chapter III and ISM Code SMS procedures.
The cargo plan must identify each CA unit by position, setpoint, and target gas composition so the watch officer can verify controller display values during rounds.
What are the USDA and EU phytosanitary compliance requirements for reefer containers?
USDA and EU phytosanitary regulations require documented cold treatment or inspection certification for many plant products before entry. Failure to comply results in cargo holds pending treatment at the discharge port — generating demurrage costs and potential cargo deterioration.
USDA cold treatment under 7 CFR Part 305
Under 7 CFR Part 305 (USDA APHIS), fresh fruits from regions with Mediterranean fruit fly or other quarantine pests must undergo approved cold treatment before or during transit to the United States. For Ceratitis capitata (Medfly), Schedule T107-a requires a core fruit temperature of −0.56°C (31°F) or below maintained for a minimum of 10 consecutive days.
Cold treatment must be monitored by temperature recording devices approved by APHIS and interfaced with the ship’s reefer monitoring system. The master or cargo superintendent provides APHIS Form PPQ 203 at the port of arrival; any gap in the temperature record triggers automatic hold and re-inspection. Shippers frequently specify recorder calibration certificates and request data download before vessel departure.
EU phytosanitary requirements under Regulation (EU) 2016/2031
Regulation (EU) 2016/2031 establishes the plant health regime for goods entering the European Union, replacing Directive 2000/29/EC. Fresh fruit, vegetables, and cut flowers from third countries generally require a phytosanitary certificate issued by the national plant protection organisation (NPPO) of the country of origin, confirming freedom from regulated pests.
For certain high-risk commodities — citrus from South Africa, stone fruit from South America — the EU additionally requires systems approaches or pre-export cold treatment, documented by an officially endorsed temperature log. The EU official controls regulation (Regulation (EU) 2017/625) mandates that Border Inspection Posts (BIPs) carry out identity and physical checks on arrival; inadequate temperature records directly trigger enhanced inspection frequency.
How is a reefer container powered on board a container ship?
Reefer containers on a container ship draw power from dedicated reefer sockets — called reefer points — fitted throughout the cargo holds and on deck. The ship’s electrical system supplies 380–460 V, 50 or 60 Hz three-phase power to each socket; the container plugs in via a flying lead, and the unit’s integral controller regulates compressor operation automatically.
Reefer points and electrical capacity
Each reefer point typically supplies 16–63 A depending on ship design and era. A fully loaded reefer container drawing 6 kW at steady state and 15 kW at pull-down represents a significant electrical load; container vessels are designed with a reefer capacity expressed as a number of plugs (e.g., 500 reefer points on a 4,000-TEU vessel).
The chief officer must verify that the reefer points allocated match the booked quantity before departure, cross-checking against the cargo manifest for commodity type and setpoint. Shore power connection at port terminals extends from the same socket design, allowing monitoring to continue during port stays.
How containers are distributed and secured throughout the vessel affects both structural loading and reefer power distribution; the container securing on ships guide covers stacking weight limits and lashing requirements that apply to reefer stacks specifically.
Genset containers
Where reefer points are insufficient or unavailable — on bulk carriers, breakbulk vessels, or when reefer capacity is exceeded — a genset container supplies its own diesel-powered electricity. The genset unit is typically stacked beneath the reefer container, connected via a short flying lead, and fuelled from a dedicated tank holding 200–400 litres of marine diesel oil.
Genset containers require refuelling approximately every 48–72 hours at full load, introducing a crew workload not present with socket-connected units. Fuel quantity, engine oil level, and coolant temperature must be recorded on each round. A failed genset in a deep-sea passage with no spare fuel is an operational emergency with direct cargo claim consequences.
What is the pre-trip inspection (PTI) procedure for a reefer container?
A pre-trip inspection (PTI) is a functional test of the refrigeration unit conducted before cargo stuffing to confirm the machine operates correctly at the nominated setpoint. PTI is an industry standard requirement specified in the Cargo Refrigeration Guidelines published by the Container Owners Association (COA) and referenced by P&I clubs in cargo claim guidance.
PTI steps in sequence
The PTI is normally conducted by a qualified reefer technician at the equipment depot or stuffing facility, not on board the vessel. The sequence runs as follows:
- Visual inspection of the unit body, door seals, drain holes, and T-bar decking for damage or obstruction.
- Power connection test: plug into a live socket and confirm the unit initiates without fault codes.
- Setpoint programming: enter the cargo’s required temperature, humidity, and ventilation rate.
- Refrigeration cycle test: run the unit for a minimum of 30 minutes and confirm supply-air and return-air temperatures converge on the setpoint.
- Data logger installation: fit a calibrated, independent temperature logger — separate from the unit’s own probe — inside the cargo space at a representative location.
- PTI certificate issued: the technician signs and hands over a PTI certificate that travels with the bill of lading. The officer of the watch should check that the certificate is on board before departure.
A missing or failed PTI certificate is the first document a P&I club surveyor will request when a cargo claim is filed. Without it, the carrier’s ability to argue the unit was in good order at loading collapses.
How do cargo claims arise from temperature excursions in reefer containers?
A temperature excursion — a deviation from the nominated setpoint lasting long enough to affect cargo quality — is the primary cause of reefer cargo claims. Claims arise from equipment failure, improper pre-cooling, power interruption at port, incorrect setpoint, or failure to maintain the unit during the voyage.
Evidence and liability chain
When receivers report damaged or deteriorated cargo, the sequence of liability investigation moves through: PTI certificate, pre-loading temperature confirmation, continuous data logger records (both unit controller and independent logger), power interruption logs from the ship’s reefer monitoring system, and the master’s protest notes.
The independent logger is critical because it records actual cargo-space temperature — not supply-air temperature. Supply-air may be at setpoint while return-air and cargo core temperatures deviate, a discrepancy the unit controller will not flag if the sensor placement is near the evaporator only.
P&I clubs and the Hague-Visby Rules
Under the Hague-Visby Rules Article III Rule 1, the carrier is obliged to exercise due diligence to make the ship — including its reefer system — seaworthy before and at the commencement of the voyage. A reefer point that delivers incorrect voltage, a monitoring system that failed to alarm, or a genset that was not refuelled constitutes unseaworthiness.
P&I clubs cover cargo liability claims, including reefer failures, subject to the carrier demonstrating due diligence. P&I clubs — the mutual insurance associations covering third-party cargo liability — require that the vessel maintain a reefer monitoring log showing setpoint, supply, and return air temperatures, and power status for each unit at regular intervals, typically every four to six hours.
Detention and demurrage arising from reefer failures
When temperature records are incomplete or deviant, port health authorities in destination countries may order the cargo held for inspection. This introduces port-side delays that trigger detention and demurrage costs, which can exceed the cargo value on high-value pharmaceutical or horticultural shipments. Carriers and shippers therefore have aligned commercial interest in maintaining rigorous PTI and monitoring protocols, even when the regulatory minimum does not explicitly require it.
Frequently Asked Questions
What temperature range does a reefer container maintain?
A standard reefer container maintains cargo-space temperatures from −30°C to +30°C. Most frozen cargoes are carried at −18°C to −25°C; chilled produce is typically between 0°C and +15°C. The actual setpoint is specified in the shipping instructions and must be programmed before stuffing.
What is a reefer point on a container ship?
A reefer point is a fixed electrical socket in a container ship’s hold or on deck that supplies 380–460 V three-phase power to a refrigerated container. The ship’s electrical system provides the power; the container’s integral refrigeration unit regulates temperature automatically. The number of reefer points determines how many refrigerated containers a vessel can carry simultaneously.
What is a genset container and when is it used?
A genset container is a diesel-powered generator unit stacked beneath a reefer container when no shipboard reefer point is available. It is used on bulk carriers, breakbulk vessels, or when a container ship’s reefer capacity is fully booked. Genset containers require regular refuelling — typically every 48–72 hours — and engine checks throughout the voyage.
What is controlled atmosphere (CA) in reefer shipping?
Controlled atmosphere refers to the modification of the gas composition inside the reefer unit, reducing oxygen and elevating CO₂ to suppress the respiration rate of climacteric fruit. A CA environment can extend shelf life by four to six weeks beyond a standard reefer carry. Oxygen levels below 19.5 % make an open CA unit a confined space requiring SCBA entry procedures.
What USDA documentation is required for cold-treated fruit shipped to the USA?
Fresh fruit subject to cold treatment under 7 CFR Part 305 must carry a continuous temperature log from APHIS-approved sensors showing the required temperature maintained for the full treatment duration — typically −0.56°C for ten or more consecutive days. APHIS Form PPQ 203 is submitted at the first US port of entry. Gaps in the temperature record trigger automatic hold.
What is a pre-trip inspection (PTI) and why does it matter for cargo claims?
A PTI is a pre-loading functional test of the reefer unit confirming it reaches and holds the nominated setpoint. The PTI certificate is the primary evidence that the refrigeration system was in good order before cargo was loaded. Without a valid PTI certificate, a carrier cannot establish due diligence under the Hague-Visby Rules if a cargo claim arises from temperature failure.
How often should reefer containers be checked during a voyage?
Industry practice and most P&I club guidance requires reefer rounds every four to six hours, with setpoint, supply-air temperature, return-air temperature, and power status recorded for each unit. Any alarm or deviation from setpoint must be logged with corrective action taken. Incomplete records are treated by surveyors as failure to exercise due diligence.
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