The air was thinning, and Bolan grew conscious of his labored breathing.

The air was thinning faster than he had imagined.

Slowly at first, it swung up a cable, climbing to the network where the air thinned.

The air would be thinning up there, and the Proctors had forgotten too much to know what to do.

The air thins gradually and, at first, the pair resist.

The corridor outside was equally chilly, and the air here was thinning as well.

The air in the lock was thinning swiftly.

The air thinned with each step, and the members of our group began staggering, pausing to try to catch a breath.

Two miles up, the thick air of Harvest thinned to Earth-normal pressure.

Somehow, the air was thinning again, although he had left the door open from the adjoining room, with a window raised beyond it.