> People have to stand back 70m until it clears.

How did they calculate that evacuation distance? CO2 is heavy. That little house about 15m from the bubble needs to be acquired.

The topography matters. If the installation is in a valley, a dome rip could make air unbreathable, because the CO2 will settle at the bottom. People have been killed by CO2 fire extinguishing systems. It takes a reasonably high concentration, a few percent, but that can happen. They need alarms and handy oxygen masks.

Installations like this probably will be in valleys, because they will be attached to wind farms. The wind turbines go in the high spots and the energy storage goes in the low spots.

The distance is likely calculated based on the stored volume and the area you cover until the height is significantly below head height (because as you point out CO2 settles to the bottom). Regarding the little house 15m from the bubble, they are not planning to build this in residential areas, so it's very unlikely that there would be a house within 15m just for operational purposes already.