diving question for a book scene

[divedummy]

Hi, I'm writing a scene in which a man freedives (so no tank) about 100 feet below the surface and encounters a chamber of air large enough for him to stand and move around.

Question: what effects does it have to emerge into air from the pressures placed on the body at 100 feet deep? Does the air feel different at that depth? And also can he safely re-enter the water?

The air in the passage would be at the same pressure as the water (about four atmospheres absolute). It wouldn't feel any different as long as he had equalized properly on the way down.

It must be stressed, however, that if he took a big breath and re-entered the water to swim back up, that it would be no different than taking a breath off a scuba cylinder at that depth. That is, if he didn't exhale heavily on the way up, he would embolize (lung overexpansion injury) and it could cause serious injury or death.

Also, if he were to spend more than about twenty minutes there, he would have a decompression obligation on the way up. If he weren't a trained scuba diver, he would be in for a world of hurt.

[divedummy]

Thanks for the info!