Air surrounds us all and without air, life—as we know it—wouldn’t exist. But what is air? And how are we able to harness its power to create domes that don’t collapse under their own weight but instead stand tall through some of the worst weather Mother Nature can throw at them?
In this first article looking at the science of air-supported structures, we’re going to talk about air and how a seemingly weightless and intangible substance is channeled for impressive feats of engineering.
The first thing to realize is that air isn’t nothing. Nothing exists—sort of—but it’s out in the vacuum of space.
Air can almost be considered a solution—a mixture of molecules all floating around and bumping into each other. A common misconception is that the molecules of air are mostly oxygen, but oxygen only comprises about 21% of the molecules in our planet’s air. The majority of air is actually nitrogen. Air molecules are about 78% nitrogen. Other trace gases make up the rest.
So with all these molecules bumping around, why don’t we see them? Well you can, you just might not notice it. Imagine a hot road in the summer. You know that distortion that you see above the asphalt that looks like the air is shimmering? This is the change in air as the concentration of molecules decreases as the temperature increases then increases again as it cools down.
As air molecules fly around and bump off each other, they create a repulsive force in the same way that two magnets will push off each other when their polarity is the same. Just like magnets, the closer you squeeze the molecules together, the more force they exert trying to separate again. This is the principle behind air pressure and the secret to how structures held up by air pressure are so strong.
A perfect demonstration of the power of air pressure is the tires of your car. Imagine the weight that pushes down on those tires and think about how much you trust in the power of air pressure to give you a smooth, comfortable, and safe ride.
Pumping more air in results in a higher amount of air molecules in the enclosed space. More air molecules creates more force against the tire walls as all the molecules fight to push off from each other. This force is air pressure and the greater the air pressure, the more strength the tire has against outside forces, like a car pushing down on it.
The same principles keep domes up.
Air pressure is strong, and so are domes. Just like a tire, the air pressure in a dome keeps the walls up. Instead of a car, though, a dome holds up against air pushing back down on it and the force of gravity. For a dome, these forces are relatively small so the inside air pressure only needs to be slightly higher than the outside pressure. (The internal pressure only needs to be 0.0036 PSI greater than the atmosphere).
Well-constructed domes and state of the art inflation systems manage the air pressure perfectly to keep domes properly inflated and ready to perform. Air structures are a feat of engineering made possible by harnessing the power of air pressure.