Unconsciousness from lack of air, if what these humans breathed could be called air, might last only a few moments.

The planet has enough oxygen in its atmosphere that humans can actually breathe it.

The humans and other life forms in this new Earth must breathe air with low oxygen content.

The oxygen content of Swoofon is very low but just enough to let humans breathe without artificial equipment.

Two thousand years later, humans would walk unaided on the surface and breathe the clear Mars air.

The sentries and all the other humans he could hear were breathing deeply and evenly.

When humans breathe the gas into their lungs, the products of its decay can cause lung cancer.

By converting water into oxygen, the electronic device allows humans to breathe underwater for days at a time.

If this stuff manufactured Vine atmosphere, how would humans breathe it?

Alice Embree once noted that humans must breathe, but corporations must make money.