[abstract] A PROVISIONAL METHOD OF OXYGEN EXPOSURE MANAGEMENT FOR A RECREATIONAL DIVE COMPUTER

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[abstract] A PROVISIONAL METHOD OF OXYGEN EXPOSURE MANAGEMENT FOR A RECREATIONAL DIVE COMPUTER

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Title: [abstract] A PROVISIONAL METHOD OF OXYGEN EXPOSURE MANAGEMENT FOR A RECREATIONAL DIVE COMPUTER
Author: Bohrer, CR; Hamilton, RW
Abstract: BACKGROUND: Increasing the fraction of oxygen in a breathing mixture effectively improves the efficiency of decompression. Unfortunately, oxygen is toxic in varying degrees depending upon the partial pressure and duration of the exposure. Various techniques have been suggested for managing a single oxygen exposure, but there is not yet available a mathematical algorithm usable in a dive computer (these have limited processing power and memory) or when developing tables that can account for multiple and multi-level exposures and for recovery between exposures. Even so, we needed a practical algorithm for use in a recreational dive computer that would warn the user when accepted limits were approached. METHODS: For limits we selected those in the 3rd edition of the NOAA Diving Manual. To deal with non-square exposures we used the interpolation method proposed by Kenyon and Hamilton (1989, XVth EUBS) which interpolates both O2 level and exposure time; this method tracks an Oxygen Limit Index (OLI), which is incremented at discreet time intervals by the ratio between the exposure time at the PO2 and the time limit for that PO2. A warning is issued when the ratio reaches 1.0, equivalent to the allowed time at a specific level. For recovery we used exponential decay, letting the OLI decrease with a half time of approximately 90 minutes when the PO2 is less than the established threshold of 0.5 atm. This allows 50% recovery in 1.5 hrs, 90% in 5, and full recovery in 9 hrs. Precise data to support this recovery rate is lacking, but it is consistent with the practice of intermittent oxygen breathing during hyperbaric therapy, and the delay between repetitive treatments. RESULTS and CONCLUSION: The algorithm has been programmed into a new recreational dive computer, the Bridge, which has been developed by Dive Rite and Seiko. Random trials of "typical" exposures show that it appears to warn conservatively when presumably acceptable exposures are exceeded, but it allows dives that are regarded as having an acceptable oxygen exposure to be displayed without a warning.
Description: Abstract of the Undersea and Hyperbaric Medical Society, Inc. Annual Scientific Meeting held July 7-10, 1993. World Trade and Convention Centre, Halifax, Nova Scotia, Canada. (http://www.uhms.org)
URI: http://archive.rubicon-foundation.org/8193
Date: 1993

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  • UHMS Meeting Abstracts
    This is a collection of the published abstracts from the Undersea and Hyperbaric Medical Society (UHMS) annual meetings.

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