There's some serious risk involved there!I'd like to point out (1st and 2ed) that even though the fireball does not create pressure, it will fill its area of effect. Very often, a good way to not get caught in a fireball was to have the mage cast it and have a second character closing the door (when there was one) as the fireball was passing. A lot of DM allowed this as it was a nice way to remove the action of one of the character. (and not all DM liked to have their players toasted by their own fireball, especially if they had been clever.)
Close the door too late and you might as well not bother. Close it too soon and, well...
And as fireball's duration is "instantaneous" that's a pretty narrow time window.