Dry ice releases gas as it sublimates and falls to -79 °C, while a gel pack is designed for around 0 °C. If box, gel pack and product have not been tested together for this scenario, the mixture is not built in the field.
The box is not sealed airtight, so the gas can leave. The dry ice sits outside the product and the gel pack, placed so that the outer packaging lets the gas escape; ventilation in vehicles and storage is considered separately.
Dry ice is subject to dangerous-goods rules by mode of transport: in air transport Class 9 and IATA PI 954 apply, and quantity and marking conditions are settled with the carrier before dispatch.
