Deep-frozen transport means dry ice for temperatures a eutectic plate cannot reach: the melting points of GEBHARDT plates run from -3 to -21 °C, while dry ice sits at about -79 °C. Dry ice is solid carbon dioxide; it does not melt but turns straight into gas, so it leaves no liquid.
The tray's job is to hold the dry ice above the load and apart from the product. A product surface in contact is exposed to -79 °C and gets damaged. Because carbon dioxide is heavier than air, the cold gas sinks and cools the volume.
The gas accumulates in a closed space. Dry ice is not carried in an airtight container, and the outer packaging must let the gas escape; in a closed cargo area a build-up is an asphyxiation risk, and the CDC advises ventilating for five minutes before entering. Dry ice is not handled bare-handed; insulated gloves and safety glasses are used. In air transport it is a Class 9 dangerous good (IATA PI 954). The quantity depends on time and volume; dry ice loaded without a calculation runs out on the road.
