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April 2008    Download the Entire Issue (PDF) Available to the Public Vol. 23, No. 4   RSS Feed for Undercurrent Issues
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When Considering Deep Stops, Profiles Rule

from the April, 2008 issue of Undercurrent   Subscribe Now

The concept of deep stops has been around for a long time. Yet it remains to be fully embraced by the diving community and likely wont be until typical recreational divers know the details.

Deep stops have advocates in the science of dive physiology. Several published studies indicate that deep stops decrease bubbles detected over the heart, and can also reduce tensions in tissue compartments. The dive organization NAUI recommends that a deep stop should be done for recreational dives deeper than 40 feet, with a one-minute stop incorporated at half of a dives max depth, followed by a two-minute safety stop at the 15- to 20-foot level.

However, there is evidence suggesting that certain types of technical dive profiles may be inappropriate for deep stops. A study from the Norwegian University of Science and Technology, using pigs as subjects in simulated dives, found that deep stops significantly reduced vascular bubbles in a long, shallow dive (100 feet for 70 minutes), but dramatically increased them in a short, very deep dive (20 minutes at 215 feet).

A U. S. Navy Experimental Diving Unit study with volunteers making training-tank tech dives to 170 feet on surface-supplied air also raised cautions regarding such stops on deep deco dives involving exercise. It reported that those who made deep stops had an increased incidence of DCS compared to those who didnt. Researchers theorized that slower off-gassing, continued gas loading, or both, may offset the benefits of reduced bubble growth from deep stops.

Clearly research on deep stops needs to be conducted in the actual recreational dive environment before meaningful conclusions can be drawn. If, how, and under what conditions deep stops may be of significant benefit are yet to be finally determined. In the meantime, the expert opinions and limited findings to date are of strong interest because they suggest that performing deep stops during routine recreational dives may reduce DCS risk. At the least, as PADI has stated, deep stops in typical recreational diving, ... probably wont hurt anything.

Until the multiple, complex issues of deep stops are being further clarified, recreational divers can feel secure by following the usual recommendations for reducing DCS. Do short and shallow profiles and slow ascents. Take long safety stops and surface intervals, and use the EAN-to-air tables.

- -Doc Vikingo

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