" Scuba divers can make it to three hundred feet breathing mixed gases, but it takes years of training and is a logistical nightmare. The danger isn’t going down—although that certainly is dangerous—it’s coming back up. For a scuba diver, a one-hour plunge at two hundred feet breathing regular compressed air would require a ten-hour ascent to purge the deadly levels of nitrogen gas in the blood that accumulate on the way down. A three-hundred-foot ascent on compressed air would most likely kill you. "

― James Nestor , Deep: Freediving, Renegade Science, and What the Ocean Tells Us about Ourselves