Rich Keller
Contributor
The depth record for both SCUBA and Hardhat is close to 600', and you need all manner of special gear and training. The 120' is the recommended limit for recreational divers now, when I started it as 190'. Around 200' oxygen in air becomes toxic and depending on time and the divers physiology so special gas mixes are used to stay there for any length of time or to go deeper.
The record is much deeper then that, I dove to 686' and that was over 30 years ago. Not sure what the record is now but I would guess somewhere in the area of about 1200'+.