Thanks Panic Mode for the idea. I will take a look into it !
Regarding your point "Skyfire". I have a fire proof steel box with a 5.000m³/h fan installed running the whole time. So about 1.3 m³/sec. So i will have a full ventilation cycle every 2 seconds. The whole Ventilation exhaust is made out of steel similar mounted like a fireplace exhaust. Do you have any idea what can be added for safety ?