Dangerous Goods Mixed Loading for Refrigerants and Solvents: IMDG Segregation, UN Marks, and Cylinder Stacking

Mon, 07 Sep 2026 · HARMONY TECHNOLOGY (ZHEJIANG) CO., LTD.

The short version: Loading Class 2.2 refrigerants together with Class 6.1 chlorinated solvents in one container is routine export practice, but it is governed by several independent technical constraints that are often conflated: IMDG segregation rules, UN packaging-mark decode, cylinder pressure–temperature limits, and IBC filling ratios. Each has a different controlling document, and getting one wrong invalidates the others.

1. Which Classes Are Actually Involved

First technical point: each refrigerant has its own UN entry — they are not interchangeable on a manifest. Single-substance refrigerants carry a dedicated UN number (R134a = UN 3159, R32 = UN 3252, R22 = UN 1018); blends are classified differently: R410A ships as UN 3163 LIQUEFIED GAS, N.O.S., while R407C has its own dedicated entry UN 3340 REFRIGERANT GAS R 407C. A manifest that treats “refrigerant” as one line item, or that reuses a single UN number across products, will be rejected — the UN number and class together drive the packing instruction and the segregation table.

2. IMDG Segregation — What Actually Applies Within One Container

IMDG segregation is expressed in four degrees: away from (1), separated from (2), separated by a complete compartment or hold from (3), separated longitudinally by an intervening complete compartment (4).

Within a single container/CTU, degrees 3 and 4 are generally unachievable — there is no intervening compartment. In practice, degrees 1 and 2 are the operable ones and must be satisfied by stowage geometry (distance, physical separation, or an intervening non-DG stow).

The controlling document is the carrier’s DG acceptance policy, which may be stricter than IMDG’s minimum. Written pre-approval from the line is what makes the stow legally executable — not the IMDG table alone.

3. UN Packaging Marks — Decoding Them

A UN mark on a cylinder or drum is not decorative; each element is a technical statement:

UN 4BA 250 / 23 / CN / M4621 / TPED
│  │   │    │    │      │
│  │   │    │    │      └─ Approval (or national scheme, e.g. TPED/ADR)
│  │   │    │    └──────── Manufacturer's serial / approval ref
│  │   │    └───────────── Country authorising the mark
│  │   └────────────────── Year of manufacture (23 = 2023)
│  └────────────────────── Pressure figure — read it with the mark it sits under:
│                          · under a UN mark this figure is the **test pressure, in kPa**
│                          · on a US DOT-4BA / 4BW cylinder it is the **service pressure, in psig**
│                          (250 bar ≈ 3,626 psi — never read the figure as 250 bar)
└───────────────────────── Packaging type code (4BA = steel cylinder, welded)

What to check before loading:

• Year of manufacture + the periodic inspection interval — gas cylinders typically require hydrostatic re-test every 5 or 10 years depending on the scheme; an expired test renders the cylinder unshippable regardless of contents.
• Test pressure ≥ the design minimum for the fill — for refrigerants, this is well above the saturation pressure at 55 °C reference temperature.
• Country authorising the mark — affects whether the destination accepts the certification scheme.

4. Cylinder Stacking and Pressure Limits

The overfill mechanism, stated precisely: a liquefied-gas cylinder filled without vapour space reaches liquid-full condition at some temperature below the design reference. Beyond that point, pressure rises hydrostatically — hundreds of bar for a few degrees — far faster than the relief device can respond. This is why filling ratio, not pressure rating alone, is the controlling number.

5. IBC Filling Ratios and Temperature Compensation

For DCM and other Class 6.1 liquids in IBCs or drums:

Practical consequence of DCM’s low boiling point (39.6 °C): in a container on deck in tropical sun, internal temperatures can exceed 50 °C. A non-pressure-rated drum or IBC is not acceptable for DCM regardless of fill level. Which packaging satisfies that requirement, and the grade parameters that travel with the shipment, are set out in Dichloromethane: specification grades, packing and export documentation.

6. Ventilation, Temperature and Stow Position

• Class 2.2 cylinders in a closed container: no forced ventilation is required for non-flammable, non-toxic gases, and a CTU that has held 2.2 cylinders is not oxygen-deficient. Oxygen displacement is a separate case, not a property of Class 2.2: it applies where a Class 2.1 cylinder has leaked inside the unit, or where a large 2.2 charge is released into an enclosed space during stripping — in those situations, treat the atmosphere as an oxygen-deficiency hazard and test it before entry.
• Class 6.1 solvents: adequate ventilation during unstuffing is required; DCM’s occupational exposure limits are low (see the product’s MSDS under the destination’s national OEL).
• Stow position: cylinders upright with valves protected; solvents in IBCs on pallets, secured against longitudinal movement per the CTU Code.

7. Planning a mixed load — step by step

1. List every line with its UN number and class. R134a = UN 3159 (2.2), R32 = UN 3252 (2.1), R22 = UN 1018 (2.2), R410A = UN 3163 (2.2), R407C = UN 3340 (2.2); DCM = UN 1593 (6.1), TCM = UN 1888, PCE = UN 1897. Never reuse one UN number across products.
2. Apply the segregation table to each class pair, keeping to the degrees achievable inside a CTU — “away from” and “separated from”. Degrees 3 and 4 require an intervening compartment and are generally not achievable.
3. Turn each degree into stow geometry — separate cylinder groups at opposite ends for “separated from”; adjacent-but-not-touching, or an intervening non-DG stow, for “away from”.
4. Check the packaging marks and cylinder dates before loading: packaging code, test pressure, year of manufacture, authorising country, and a current hydrostatic test date per cylinder.
5. Set the fill. Cylinder filling ratio per P200 for each gas; IBC or drum ullage of at least 2 % at 55 °C computed for the maximum expected transport temperature.
6. Confirm ventilation and stow position. No forced ventilation is required for Class 2.2, but unstuffing Class 6.1 solvents needs ventilation; test the atmosphere before entry if a Class 2.1 cylinder has leaked. Stow cylinders upright with valves protected and secure the load against longitudinal movement per the CTU Code.
7. Get the carrier’s written DG pre-approval against the stated data — the line’s policy may be stricter than IMDG’s minimum, and that pre-approval is what makes the stow executable.

Technical reference on dangerous-goods stowage for refrigerant and chlorinated-solvent cargoes. Requirements differ by mode (IMDG for sea, ADR/RID for road/rail, IATA for air) and by carrier. This note describes IMDG sea-transport constraints; the applicable edition for a given shipment and the carrier’s own DG policy govern in case of conflict.

FAQ

Can refrigerant cylinders and chlorinated solvents ship in one container? Yes, subject to IMDG segregation — degrees 1 and 2 (“away from”, “separated from”) are the operable ones inside a CTU, since degrees 3 and 4 require intervening compartments. The carrier’s DG policy governs.

Do R32 and R134a share a UN number? No — and this is the most common error on a mixed-load manifest. R32 is UN 3252, Class 2.1 (flammable gas); R134a is UN 3159, Class 2.2 (non-flammable, non-toxic gas). They may travel in the same container, but each keeps its own UN number, class and packing instruction.

Is a refrigerant blend classified the same way as a single-substance refrigerant? No. Single substances carry a dedicated entry (R134a = UN 3159, R32 = UN 3252, R22 = UN 1018). Blends do not necessarily: R410A ships as UN 3163 LIQUEFIED GAS, N.O.S., while R407C has its own entry, UN 3340 REFRIGERANT GAS R 407C.

What does a UN packaging mark contain? Packaging type code, test pressure in bar, year of manufacture, authorising country, and approval reference — each element is a technical statement. Cylinder re-test intervals apply independently of contents.

Why is filling ratio the controlling number for liquefied gas? A cylinder filled without vapour space reaches liquid-full condition on warming; pressure then rises hydrostatically — hundreds of bar for a few degrees — far faster than any relief device can respond.

Related reading

• Classification decides the paperwork before the load does — how HFC blends and single substances are entered and why the line item follows the composition: HS codes 2026 — classification of mixtures
• Packaging choice where the substance boils below 40 °C — why packaging for a low-boiling solvent is a pressure problem, not a volume problem: DCM specification, packing and export documents
• The documents that must agree with the load — what a batch certificate has to show for the packing list and declaration to reconcile: Reading a COA

What we can provide

For a mixed cargo we can supply the loading and segregation plan for the actual combination, built from the classes and UN numbers above:

• Segregation by combination — which pairs move as “away from” or “separated from” inside one CTU, and the stow geometry used to satisfy each degree (cylinder group separation, an intervening non-DG stow, opposite-end stowing).
• Packaging and mark check — packaging code, test pressure, UN mark and cylinder hydrostatic test date verified per product before loading.
• Filling-ratio calculation — cylinder filling ratios per P200 for each gas, and IBC or drum ullage calculated for the maximum expected transport temperature rather than the loading temperature.
• Transport data set — UN number, class, packing group, proper shipping name and packing instruction for every line in the container, so carrier pre-approval can be sought against stated data rather than assumed.

Contact us with: the product list with quantities, the packaging types, and the loading and discharge ports.

Sources

• IMDG Code (International Maritime Organization): the segregation table (7.2.4), packing instructions P200 / P001 and the CTU stowage guidance — https://www.imo.org/
• 49 CFR 177.848 — segregation and separation of hazardous materials (Cornell Law School, Legal Information Institute / eCFR) — https://www.law.cornell.edu/cfr/text/49/177.848
• 49 CFR 180.205 — periodic requalification of pressure receptacles (Cornell Law School, Legal Information Institute / eCFR) — https://www.law.cornell.edu/cfr/text/49/180.205
• ASHRAE Standard 34 — designation and safety classification of refrigerants (ASHRAE): the basis for the safety classes used above — https://www.ashrae.org/

Prepared by HARMONY TECHNOLOGY (ZHEJIANG) CO., LTD. — trading company; the group’s operating entity for this product line.