BIOMARINE BIOPAK 60

The BioPak 60 (figures 3-4) is a compressed-O2, closedcircuitapparatus with a refillable CO2-absorbent canister. Itwas certified by NIOSH in 1978. It was certified again in 1988 as a positive-pressure device after that classification was added in 1985. It contains approximately 170 L of O2 if filled to the recommended cylinder pressure of 2,250 psi.2 A constant flow of 1.9 L O2/min (ATPD) plus a volume-activated demand valve constitute the O2-delivery system. The relief valve is also volume-activated. The CO2 absorbent is Sodasorb, a form of soda lime. The low-pressure alarm sounds at approximately 25% of capacity.

The user exhales into the face mask containing both inhalation and exhalation check valves, through the exhalation hose, through the CO2-absorbent canister, and into the breathing bag consisting of a spring-loaded, rigid diaphragm and a flexible sleeve. The CO2-absorbent canister and breathing bag are contained within the breathing chamber, as Biomarine calls it. Upon inhalation, the air is drawn from the breathing bag through the inhalation hose and check valve, and then into the face mask. An anoxia-prevention valve, located in the exhalation hose at the point that it enters the breathing chamber, blocks exhalation flow unless opened by pressure provided by the O2 cylinder. This prevents use of the apparatus unless the O2 cylinder is opened and pressurized. It also signals the user when the cylinder is empty by preventing exhalation into the circuit. The flow path through the breathing chamber is relatively complex. The exhaled air enters an inlet plenum between the CO2-absorbent canister and a solid plate separating it from the breathing bag. The O2 constant flow enters the circuit at this point, also. The exhaled air then travels through the absorbent to an outlet plenum formed by the canister and the lid of the breathing chamber. The exhaled air is then routed around coolant rings containing sodium phosphate crystals, through slots around the circumference of the housing, and into the breathing bag. The spring-loading on the diaphragm results in a positive static pressure in the breathing circuit. The term "positivepressure" is derived from this feature. When the user demands more air than is contained in the breathing bag, the diaphragm presses against a demand valve, which causes O2 to flow into the bag. The flow of O2 from the bypass valve is delivered to the bag at a location on its circumference. If more air is exhaled into the breathing bag than it can hold, the diaphragm resses against a relief valve and vents the excess volume.