There was an air vent in the firewall of the Tiger 1. It connected the crew compartment to the engine compartment. I believe it was used to pass hot air to the crew in cold weather (the vehicle had no heater for the crew.)
According to the Tigerfibel [2] , you should not open this vent when the crew hatches are closed. Otherwise, engine air will enter the crew compartment. I believe the problem here was the danger of carbon monoxide poisoning in a sealed vehicle.
Several different designs of vent were used. This diagram shows the first design, seen from the front side. This design with 4 holes was used only in vehicles with a HL 210 engine, that is, the first 250 vehicles [1] .
Here are the dimensions of the vent holes [1] . There was a small lever between them, located exactly on the center line of the tank. This lever opened and closed the vent. The diagram shows the closed position.
This model shows the vent mechanism on the rear side of the firewall.
The lever was attached to a circular cam, which caused a panel to slide between two guide rails. In the open position, holes in the panel would align with holes in the firewall.
Below is part of a sketch from the Tigerfibel [2, see page 20] that explains the controls on the firewall. The black lettering was present on the tank, but the red numbers are in the diagram only.
The lever could travel about 180 degrees. Its positions were marked 'Auf' for open, and 'Zu' for closed. (These markings have not been preserved in the Bovington museum's vehicle. Also, the restorers have put the handle the wrong way around.)
[1] Survey of vehicle 250122, Bovington, by David Byrden
[2] Tigerfibel (user's guide for the Tiger 1)