A clinical trial shipment leaves a Cambridge facility on a Tuesday afternoon, bound for a site in the EU. The samples are packed, the temperature logger is running, the courier picks it up. It gets to Logan and stops. The dangerous goods desk finds the net weight of dry ice missing from the air waybill. The box goes back on a truck. The samples sit while someone reprints paperwork. A shipment that was thermally fine misses its flight because of one blank field.
That is the failure mode with air-shipped dry ice. Not the cold chain. The paperwork. Dry ice is a regulated dangerous good the moment it enters an aircraft, and the rules that govern it are specific, boring, and enforced by people whose entire job is to reject non-compliant packages. If you ship biologics or clinical samples by air out of the Northeast, PI 954 is the document that decides whether your box flies.
Why dry ice is a dangerous good in the first place
Solid carbon dioxide sublimates. It goes from solid straight to gas at −78.5 °C, releasing CO₂ the entire time it exists. On a loading dock that gas dissipates into the room and nobody notices. Inside the sealed, pressurized hull of an aircraft, there is nowhere for it to go. Enough CO₂ in an enclosed volume displaces oxygen, and the air the crew breathes stops being the air they trained on.
That is the whole reason dry ice is classified as UN 1845, Class 9 (miscellaneous dangerous goods) under the IATA Dangerous Goods Regulations. It is not toxic, flammable, or corrosive. The hazard is asphyxiation risk in a confined space, plus the pressure a sealed container of subliming CO₂ can build. Both hazards drive the packing rules.
PI 954 in one paragraph
Packing Instruction 954 is the IATA rule for offering dry ice as a refrigerant for air transport. It applies on both passenger and cargo aircraft. When dry ice is cooling non-dangerous contents such as biological samples, food, or most pharmaceuticals, the ceiling is 200 kg of dry ice per package. The package has to be built to vent CO₂ gas so pressure cannot build up and rupture it. And the package plus the air waybill have to carry a specific set of marks. Miss any one of them and the shipment is non-compliant.
The package: it has to breathe
This is the requirement people get wrong when they improvise. A dry ice package under PI 954 must be designed and constructed to permit the release of carbon dioxide gas and to prevent a build-up of pressure that could rupture the packaging.
In practice that means you do not use a hermetically sealed container. You do not tape a Styrofoam box shut and wrap it in cling film. EPS (expanded polystyrene) shippers and validated VIP-paneled boxes are used because they vent at the seams by design. If you have upgraded to a gasketed container for thermal performance, confirm it is rated to vent CO₂. A sealed, gas-tight box holding subliming dry ice is a pressure vessel, and it will be rejected on sight by a trained acceptance agent.
The four marks every package needs
An acceptance checklist reads the outside of the box before anyone opens it. Four things have to be present and legible:
1. The proper shipping name and UN number. "Dry ice" or "Carbon dioxide, solid," and "UN 1845," marked on the package.
2. The Class 9 dangerous goods label. The miscellaneous hazard diamond, applied to the package.
3. The net weight of dry ice, in kilograms. Per package. This is the number the loading math depends on, and it is the one most often left off.
4. Shipper and consignee names and addresses. Full, on the package.
For an overpack (several boxes consolidated into one unit), the total net weight of dry ice across the overpack goes on the outside, and the overpack is marked to show the marks inside are still valid.
The air waybill line that grounds shipments
Here is the field that stops more shipments than any packaging defect. The "Nature and Quantity of Goods" box on the air waybill (or the alternate transport document) must contain three things: "UN 1845," the words "Dry ice" or "Carbon dioxide, solid," and the net weight of dry ice in kilograms.
The net weight is the part people skip. The box says "clinical samples" and stops there. An acceptance agent cannot process that. The dry ice weight is what the carrier feeds into its per-flight CO₂ budget, and without it, the shipment cannot be loaded. If you take one thing from this post: the net kilograms of dry ice belong on both the package and the air waybill, every time.
Why the carrier's limit is not your limit
PI 954 caps a package at 200 kg. But the carrier may accept far less, and the number changes by aircraft and by season. That is not the carrier being difficult. Every hull has a fixed CO₂ budget set by its ventilated volume, its air exchange rate, and an assumed sublimation rate. Your dry ice competes with everyone else's for that budget on that specific tail.
The practical consequence: a booking that cleared in March can come back capped in July, when everyone in the Northeast is moving temperature-sensitive product at once. Nothing changed about your box. The aircraft filled its CO₂ allowance with other people's boxes. Plan air-freight dry ice loads against the carrier's stated per-shipment cap, not the 200 kg regulatory ceiling, and book early in peak season.
Pack the right amount, not the most
Because dry ice sublimates continuously, the weight you declare at tender is already falling by the time the box is loaded. Over-packing to be safe has three costs: it eats into the carrier's CO₂ budget, it pushes you toward the per-shipment cap faster, and it wastes product. Under-packing loses the payload.
The way out is to size the charge to the actual lane. A well-characterized pack-out for a 48-hour door-to-door route to Europe out of Boston or Newark uses a validated shipper, a known sublimation rate for that container, and a documented fill weight, not a habit carried over from the last shipment. Pellet gives up more mass per hour than slab or block because of surface area, so pellet-packed air shipments run higher. Match the form to the container and the transit time.
Questions we get asked
Does PI 954 require dangerous goods training to ship dry ice? Shipping dry ice by air requires the shipper to prepare it correctly under the IATA DGR, and personnel who prepare these shipments are expected to be trained appropriately. Many organizations designate and train specific people rather than leave it to whoever is packing that day. Confirm your process with your carrier and your quality group.
Can I ship dry ice on a passenger flight? Yes. PI 954 applies to both passenger and cargo aircraft, up to 200 kg per package, subject to the individual carrier's accepted limit.
What if the samples themselves are dangerous goods? Then you have two hazards, the contents and the dry ice, and both have to be declared and packed to their respective instructions. Category A and B biological substances have their own rules layered on top of PI 954. Treat that as a separate, more involved workflow.
Do I mark the net weight in kilograms or pounds? Kilograms. The DGR is metric. Convert before you mark and before you complete the air waybill.
Does the box need to be a specific brand or spec? No brand requirement. It needs to vent CO₂, hold the payload at temperature for the transit time, and survive normal handling. Validated EPS and VIP shippers meet this. A random cooler does not.
The summary, on one line
Dry ice by air is UN 1845, Class 9, packed under PI 954: vent the package, apply the four marks, and put "UN 1845, Dry ice, net kg" on the air waybill. Size the charge to the lane, respect the carrier's per-flight cap, and book early in summer.
Cryo Life Solutions supplies pelletized and slab dry ice for biotech, pharma, and clinical trial cold chain across the Northeast US. We support air-freight pack-outs with documented fill weights and validated shipper guidance, and operate under documented GMP-aligned procedures while working toward full GMP certification. Standing orders and delivery available across MA, NH, RI, CT, NY, NJ, and PA. Call 603-802-6650 or email info@cryolifesolutions.com.
Related reading: Dry Ice for Biotech and Pharma Cold Chain: A Working Guide for Northeast US Operators
