Excessive air pressure when removing 1992 Lumina gas cap

Does anyone know what causes this? You can hear a surge of air each time the gas cap is removed

did you let the tank go REALLY low? If you haven't filled up in a while, I think the pressure has just built up and it has to go somewhere.

is it pressure or vacuum that you are hearing hiss out? I know that OBDII uses sort of a map sensor and manifold vacuum to monitor the integrity of the fuel system aginst venting fuel favor. OBD1 does not though (that i am aware of). May just be somethnig you have to get used to.

Does anyone know what causes this? You can hear a surge of air each time the gas cap is removed
I recently got this low mileage 92 Lumina and noticed the pressure build up when opened the gas cap. The manual says it is normal so I'm not going to do anything about it. Let me know if you could fix it. By the way, lumina seems to be far better than I expected, great car so far.