Air pressure differences in an inflated dome

[Korvan]

Here in Vancouver, BC, they are replacing the roof on BC Place Stadium, which used to be one of the largest inflated domes in the world. The dome is kept "raised" by an increased air pressure inside. Surprisingly enough, the pressure difference between the inside and outside is only 250 Pa, which is about 0.25% of atmospheric pressure. This pressure in maintained in part through the use of airlocks at entry and exit points. (nothing too fancy, revolving doors with rubber seals for the most part).

Once in a while when they need to move a large number of people out of the stadium, they will just open normal sliding doors and allow some air to escape while people exited the stadium. I got to experience this one time, and it was something else! Approaching the open door, even up to a step away, you could barely feel any air movement at all, but once you stepped through the door, it was like being picked up and thrown out by an angry bouncer. You literally had to start running to keep your feet. The feeling of wind around you was greater than anything I've experienced before (except for maybe a small water spout I got caught in, that one was strong enough to pick up a deck chair, lift it about 5 feet and drop it into the lake).

I was most amazed at the difference one step could make, going from near calm to gale force winds. I'm guessing the reason for this is that the air lost through the door was such a small fraction of the air inside the stadium, air could flow towards the door in large volumes, but low speed. The violence of the flow outside the door was impressive though, and that was just a 250 Pa difference in pressure. Hard to imagine what a full atmosphere difference (such as a blowout in space) would be like. Still, if the vessel was large enough, you might not be able to tell until you got quite close to the leak, unlike what is commonly shown in movies and TV.

[Hawkwings]

250 Pa is still 250 newtons per square meter. A human cross-section looks to be a bit more than a square meter, so there you go.

Air is surprising stuff. I went flying in a little Piper Archer last week, and as we were pushing it out from its parking spot, we were kind of marveling at how air could actually lift the whole plane up into the sky.

[J]

I guess it's a bit like having a vacuum cleaner in the regular suction mode versus putting it in reverse so it blows. The air pressure differential is probably pretty close in both modes yet the range of its effects is drastically different. When the vacuum cleaner is sucking it's not going to pick up anything from more than a few centimetres away, when it's blowing it can blow around papers and stuff from several metres across a room.

[Korvan]

I guess it's a bit like having a vacuum cleaner in the regular suction mode versus putting it in reverse so it blows. The air pressure differential is probably pretty close in both modes yet the range of its effects is drastically different. When the vacuum cleaner is sucking it's not going to pick up anything from more than a few centimetres away, when it's blowing it can blow around papers and stuff from several metres across a room.

That's pretty much it. It was just a surprising effect seeing that big of a difference in air flow from taking just one step. It was a hell of a lot fun too, I'm sorry that I only got to experience it the one time before they changed the roof of the stadium.