Freedivers are all about diving as far down as they can, ever trying to beat the last great attempt. They don't wear oxygen tanks -- they voluntarily deal in apnea, the cessation of breath. They dive down either with their own power, aided by weights, or strapping themselves into a machine known as "no limits," and come up at the last second with a balloon-style flotation device -- basically an Opposite Day parachute.
These are people who have painstakingly taught themselves to survive up to 9 minutes, 24 seconds without air, and it is precisely as dangerous as it sounds: There are around 5,000 freedivers in the world, and an estimated 100 of them die every year. That's 2 percent of your entire sport just up and dying on an annual basis, and the people who perish are not just overconfident rookies: In 2015, Natalia Molchanova, the greatest superstar of the sport, never surfaced from a freedive that she was doing just for shits and giggles.
At that depth, shits and giggles are both fatal.