Since the greatest changes in gas pressure occur in the first 33 feet of depth, "swallow" dives, as in 10 feet or so might be far more dangerous for the unprepared and untrained "diver" than they are thinking.
"Scuba diving in shallow water, usually regarded as safe, causes the bends in dozens of Australians each year, a conference was told yesterday. ... "It is now clear that even shallow waterdives can produce decompression sickness," said Dr Griffiths, director of the Hyperbaric Medical Unit at Townsville Hospital.May 15, 2002
Bends warning on diving in shallow water - theage.com.au
"Scuba diving in shallow water, usually regarded as safe, causes the bends in dozens of Australians each year, a conference was told yesterday. ... "It is now clear that even shallow waterdives can produce decompression sickness," said Dr Griffiths, director of the Hyperbaric Medical Unit at Townsville Hospital.May 15, 2002
Bends warning on diving in shallow water - theage.com.au