Air bubble
Raaya had no problems doing that. 20 minutes was exactly her limit to holding her breath successfully but the other were totally different. The highest of them was Myra which was 15 minutes and even still that was many many second away from the time she had estimated.
What if they met a mishap?
"20 minutes? We can't hold our breaths that long! We'll suffocate and die!" Reid complained. 20 minutes was enough for him to suffocate, die and be cremated all together.
"Do you think we don't know that?" Myra rolled her eyes at him.
"how then do we cross successfully?" Curtis asked again "is there anything that can help us hold our breath, or perhaps purify the air we breath."
There was nothing. They didn't even know what poison was in the air so finding an antidote was impossible.