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SIEBE GORMAN PROTO TEN
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The Proto Ten (figures 26-27) is a compressed-O2, closedcircuit
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apparatus with a refillable CO2-absorbent canister. It
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was certified by the USBM in 1968 as a 3-hr apparatus. The
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cylinder contains 400 L ATPD of O2 when filled to 2,840 psi at
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room temperature. A constant O2 flow of 1.5 L/min ATPD is
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provided and augmented by a pressure-activated demand valve.
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The relief valve is also pressure-activated. The CO2 absorbent
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is Protosorb, a soda lime composed mostly of CaOH.
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Exhaled air from the face mask passes through the exhalation
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hose and check valve through the radial CO2-absorbent canister
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housed in a metal shell, which also contains an inverse
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breathing bag, a heat-absorbent canister, and a warning whistle.
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The breathing circuit air is contained within the metal shell and
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contacts the exterior of the breathing bag, the interior of which
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is open to ambient. Air is inhaled from the shell interior,
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through a metal tube connected to the heat-absorbent canister,
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through the inhalation check valve and hose, and back to the
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face mask.
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The inverse breathing bag design results in the breathing
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circuit air contacting the metal shell, enabling heat to be
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radiated to air in a plenum vented to ambient. A chamois cloth
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jacket covers the exterior of the metal shell. The jacket is
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wetted from water coming from the ice melting in the heatabsorbent
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canister, which is wicked through a hole in the
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canister to two positions on each side of the surface of the shell.
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The water in the chamois jacket evaporating to ambient cools
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the surface of the metal shell. Heat is transferred to ambient
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also through the breathing bag, which pulls ambient air into it
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with each breath. A sponge at the bottom of the inside of the
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metal shell, under the CO2-absorbent canister, holds the water
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released by the chemical reaction.
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