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October 2017    Download the Entire Issue (PDF) Available to the Public Vol. 43, No. 10   RSS Feed for Undercurrent Issues
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Diving in Freezing Water? U.S. Navy Tests Flunk Some Regulators

from the October, 2017 issue of Undercurrent   Subscribe Now

Diving in Freezing Water? U.S. Navy Tests Flunk Some Regulators

It's unlikely that many Undercurrent readers regularly dive in cold water unless they are visiting a freshwater lake or deep wreck diving, but someday you might take a trip to Iceland's Silfra or join one of Amos Nachoum's trips to the Antarctic or Norway.

That said, since the depressurization of gas in a regulator results in a simultaneous drop in temperature, any water 50F (10C) or less can cause a regulator to freeze and malfunction. The first-stage may jam, resulting in increased inter-stage pressure that the second-stage cannot control, causing a free-flow, or, in a worse case, even occluding air-flow because of an ice build-up in the second-stage.

Researchers from The U.S. Navy Experimental Diving Unit and the University of California, San Diego, tested the performance of regulators for under-ice diving operations, during which 17 science divers logged 305 dives in seawater close to freezing under 20-foot (6m) - thick ice in Antarctica. Seventeen different regulators from 12 manufacturers (69 in total) were randomly assigned to divers. There were 65 incidents of free-flows.

Due to the risk of regulator failure, the divers were equipped with two independent regulators on a tank Y-valve with drysuit direct-feeds supplied from the backup regulator. All the downstream regulators were equipped with an isolator valve inline on the intermediate pressure hose. Recently, the U.S. Navy has recommended the Zeagle isolator valve for freezing water temperatures, in conjunction with a high-pressure relief valve.

Besides water temperature affecting whether a regulator freezes, airflow, moisture in exhaled breath, and whether or not it was breathed from in cold atmosphere before immersion, can also affect freezing.

"Contrary to expectations, the pooled incidences for the seven best performing regulators was significantly different from the 10 remaining regulators. Those regulators deemed acceptable -- their failure rate was less than 11 percent -- were the Dive-Rite Jetstream, Sherwood Maximus SRB3600 and SRB7600, Poseidon Jetstream, Cyklon and Xstream Deep, and Mares USN22 Abyss." The report did not list those that were unacceptable.

The report concludes that those diving under ice must constantly be on their guard. "Because of the pressures of the marketplace, scuba regulator models typically have a short half-life. However, designing a regulator tolerant to freeze-up is a black art for most manufacturers, and even 'minor' cosmetic changes can affect 'freeze-up' risk."

(Performance of life support breathing apparatus for under-ice diving operations. UHM 2017 Vol 44, No.4 Michael A Lang PhD, John R. Clarke PhD)

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