To expand further, oxygen is toxic at 1.6ATA. For those unfamiliar, pressure doubles every 10m (33ft). So if I tried to breath 100% oxygen at 33ft (aka 2.0ATA), I’d die pretty quickly. At 66ft, that caps you at about 40% oxygen. At 99ft, you essentially can’t breath any higher oxygen concentration than natural air.
As such, nitrox’s purpose isn’t to increase depth. It’s actually used to increase bottom time (at a loss of max depth) without needing decompression. You get this increased bottom time due to lower amounts of nitrogen.
I’ve logged hundreds of nitrox dives from 28% - 60% oxygen levels, but never bit the bullet and gotten into more advanced air mixtures like Trimix. Trimix and other specialty blends are hard to get air fills for at the places I most commonly dive, so I keep pushing it off.
