The trays are placed inside the blast chiller and then a fan blows chilled air over the food, rapidly cooling it down. The rapid cooling reduces loss from evaporation during the cooling process and minimizes the size of the ice crystals that form in the food when it is frozen.
The idea of this type of freezer storage is to very rapidly bring down the temperature of (usually) foodstuffs or fresh produce, freezing them very quickly
The temperature range of a blast freezer varies depending on the manufacturer, but one thing is a fact; it is much colder than your average domestic freezer. The common range of blast freezers and chillers are designed with temperature ranges of -40°C to +10°C.