http://en.wikipedia.org/wiki/Technical_diving
Also check out Nuno Gomez , he holds the world record of 318 m using scuba gear - and a variety of gas mixes to achieve such depths .
thats app 1000 feet .
Also there is a big case up here about professional diver sueing the goverment foerwhat they went through after working at depths from 70 to over 200 meters in the 1980s and 1990s.
So -that is several hundred meters -and several hundred feet as well .