Dry ice, the solid form of carbon dioxide, is an indispensable cooling agent for shipping temperature-sensitive goods like pharmaceuticals and perishable foods. Its unique refrigerating capability stems from sublimation, where it changes directly from a solid into a gas. Safe transportation is specialized because this phase transition and the substance’s extremely low temperature create distinct physical hazards. Specific packaging protocols are mandatory to prevent container failure and protect handlers throughout the shipping chain.
Unique Challenges of Solid Carbon Dioxide
The two primary properties dictating packaging requirements are intense cold and behavior during the phase change. Dry ice maintains a temperature of approximately \(-109.3^\circ\text{F}\) (or \(-78.5^\circ\text{C}\)), cold enough to cause severe frostbite or “cold burns” upon direct contact. This extreme temperature necessitates robust insulation to slow the sublimation rate and maintain cooling for the duration of the shipment.
The most significant challenge is the physical expansion that occurs during sublimation. As the solid warms, it converts into gaseous carbon dioxide, which can expand up to 800 times its original volume. If placed inside an airtight container, the rapidly expanding gas generates immense internal pressure. This pressure buildup can quickly cause the package to rupture violently, posing an explosion hazard. Consequently, no dry ice package can ever be completely sealed.
Insulating Materials and Container Selection
The packaging system is designed to balance insulation and breathability. The primary insulating material is almost universally Expanded Polystyrene (EPS) foam, often called a Styrofoam box. EPS foam is selected for its light weight and high thermal resistance, typically around R-4 per inch of thickness, which minimizes heat transfer.
The EPS foam container must be secured inside a durable outer container, usually a heavy-duty corrugated cardboard box. This outer shell provides structural integrity, protects the fragile foam, and offers a smooth surface for hazard labeling. To further maintain a cold environment, non-compacting void fill material, such as wadded paper or packing peanuts, is used to eliminate air space and prevent the dry ice from shifting.
The product being cooled is often wrapped in a separate, unsealed plastic liner before placement in the insulated core. This liner protects the product from direct contact with the dry ice and provides a barrier against condensing moisture. The thickness of the EPS foam is determined by the shipment’s expected transit time, as thicker walls provide a higher R-value and longer cooling duration.
Ensuring Proper Ventilation and Containment
The most important physical requirement for safe shipping is ensuring a clear mechanism for the carbon dioxide gas to escape. This is achieved using packaging components that are not completely sealed, such as insulated lids that rest loosely or outer boxes incorporating pre-punched vent holes. Shippers must never use tape to seal the insulated foam core shut, as this defeats the venting mechanism and risks a pressure rupture.
The shipment must be clearly marked and labeled to communicate the hazard to all handlers. Dry ice is classified as a Class 9 Miscellaneous Hazardous Material under transportation regulations. The exterior must display the Class 9 hazard label, the proper shipping name (“Dry Ice” or “Carbon Dioxide, Solid”), and the United Nations identification number, UN 1845.
A specific marking must also indicate the net weight of the dry ice in kilograms. These labels alert cargo handlers to the asphyxiation hazard, as the sublimated gas is heavier than air and can accumulate in confined spaces. Furthermore, personnel handling the dry ice should wear appropriate personal protective equipment, such as insulated gloves, to prevent cryogenic burns.