If a truck or trailer is equipped with such a ‘cat flap’, it usually concerns refrigerated or freezer vehicles. Because the doors of these types of trucks close very well, the air would quickly become stale if the temperature rises after unloading, or if the vehicle is not cooled. This could quickly cause germs or fungi to form as a result of condensation.
The effect can be compared to a refrigerator being switched off with the door closed. After a week, the refrigerator will be full of mold and mildew. The small flap in the back of trucks or trailers is used to ventilate the cargo area when not in use or when the cooling system is turned off. So when you see a refrigerated truck driving with the hatch open, you know it is empty.
The open tailgate is only bled during the journey by the negative pressure of the air flow behind the truck. This is because there is often one at the front, high at the top. This way it will continue on its journey. You can’t just look through the open shutters: they either have an inside or outside grille, or a sheet metal labyrinth to prevent foreign objects – or cats – from entering.
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