When a sample is damaged in transit, the cost is rarely the sample itself. It is the repeat collection, the delayed result and, in clinical or forensic contexts, the compromised decision that followed. That is why sample transport is specified as a containment system rather than purchased as a box.
Three Layers, Three Jobs
| Layer | Job | Typical failure |
|---|---|---|
| Primary container | Holds the sample directly | Cap loosens under vibration or pressure change |
| Secondary container | Contains any leak from the primary | Wrong size, or absorbs rather than contains |
| Outer case | Protects both from impact, weather and handling | Shell survives but contents are crushed or warmed |
A rigid outer case with a cut or thermoformed cavity holds the secondary container in position. That matters more than it sounds: a secondary vessel rattling inside a case is being repeatedly impacted, and a rigid bottle impacting a rigid shell transmits almost everything.
Temperature: Define the Band, Then the Duration
Cold chain is not one requirement but three numbers — the target band, the acceptable excursion, and the duration the case must hold it. Refrigerated and frozen transport are different engineering problems, and ambient shipments with a narrow tolerance have their own constraints.
- Refrigerated (typically 2–8 °C). Gel packs conditioned to the right temperature; over-conditioned packs freeze sensitive samples.
- Frozen. Dry ice or phase-change material, with attention to venting where dry ice is used.
- Controlled ambient. Insulation works both ways — it protects against a hot vehicle as well as a cold one.
Insulation thickness and payload mass are traded against each other. The practical method is to qualify the packed configuration: pack as it will actually ship, instrument it, and run the realistic worst-case journey.
Marking and Handling
- Orientation markings where the contents must stay upright.
- Fragile and handling symbols that survive being scuffed.
- External documentation pouch so paperwork is not lost and the case need not be opened at checkpoints.
- Temperature indicator or logger where excursion evidence is required.
- Applicable regulatory markings for the classification being shipped — these depend on what is inside and are the shipper's responsibility to apply correctly.
Cleaning Between Runs
Reusable transport cases need a cleaning routine, because contamination between runs undermines the sample. Choose smooth, non-porous liner surfaces that can be wiped with a compatible disinfectant, and avoid open-cell foam in direct contact with vessels — closed-cell or skinned materials clean far better.