They have to get topside quite regularly in order to breathe.

I think your partner's already dead back there, and you will be, too, if you don't get topside in a hurry.

No have got topside, all same bottomside have got.

"Let's just get topside and see what plays out from there."

"We'll have to get topside fast," Tom thought, "even though it means risking the bends."