Physiologic Basis for CO2 Limits Within Semiclosed and Closed-Circuit Underwater Breathing Apparatus

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Physiologic Basis for CO2 Limits Within Semiclosed and Closed-Circuit Underwater Breathing Apparatus

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Title: Physiologic Basis for CO2 Limits Within Semiclosed and Closed-Circuit Underwater Breathing Apparatus
Author: Knafelc, ME
Abstract: Semiclosed- and closed-circuit underwater breathing apparatus (UBA) incorporate a canister filled with carbon dioxide (CO2) absorbent material. As the absorbent becomes expended, the CO2 level within the breathing loop will rise. Currently, CO2 absorbent canisters are considered expended when the effluent CO2 is 0.5percent Surface Equivalent Value (SEV). In the past, this value often represented the threshold between the linear and the exponential rise in effluent CO2. The 0.5percent SEV limit was used to reduce the diver's risk for experiencing excessive levels of CO2. However, with advances in absorbent canister design, this value may be overly conservative. Because the overall respiratory load of a UBA can compound the effect of the inspired CO2, the improved breathing performance of some current UBAs also warrants reevaluating the current limit. This literature review specifically looked at low levels of CO2 affecting work and mental performance, nitrogen narcosis, decompression sickness and central nervous system (CNS) oxygen toxicity to determine if the breakthrough limit could be changed.
Description: Citation Status: Active; Citation Classification: Unclassified; Title Classification: Unclassified; Report Classification: Unclassified; Identifier Classification: Unclassified; Abstract Classification: Unclassified; Distribution Limitation(s): 01 - APPROVED FOR PUBLIC RELEASE; Information provided by the Department of Defense and the Defense Technical Information Center (http://www.dtic.mil/) is considered public information and may be distributed or copied unless otherwise specified. Use of appropriate byline/photo/image credits is requested.
URI: http://archive.rubicon-foundation.org/3304
Date: 2000

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