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Oxygen Content in Semi-Closed Rebreathing Apparatuses for Underwater Use. Measurements and Modeling

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Doctoral Thesis in Technology and Health Stockholm, Sweden 2015 Oxygen content in semi-closed rebreathing apparatuses for underwater use. Measurements and modeling OSKAR FRÅNBERG KTH ROYAL INSTITUTE OF TECHNOLOGY ENGINEERING SCIENCES Oxygen content in semi-closed rebreathing apparatuses for underwater use. Measurements and modeling OSKAR FRÅNBERG Doctoral thesis No. 6 2015 KTH Royal Institute of Technology Engineering Sciences Department of Environmental Physiology SE-171 65, Solna, Sweden ii TRITA-STH Report 2015:6 ISSN 1653-3836 ISRN/KTH/STH/2015:6-SE ISBN 978-91-7595-616-9 Akademisk avhandling som med tillstånd av KTH i Stockholm framlägges till offentlig granskning för avläggande av teknisk doktorsexamen fredagen den 25/9 2015 kl. 09:00 i sal D2 KTH, Lindstedtsvägen 5, Stockholm. iii Messen ist wissen, aber messen ohne Wissen ist kein Wissen Werner von Siemens Å meta e å veta Som man säger på den Kungliga Tekniska Högskolan i Hufvudstaden Att mäta är att väta Som man säger i dykeriforskning Till min familj Olivia, Artur och Filip iv v Abstract The present series of unmanned hyperbaric tests were conducted in order to investigate the oxygen fraction variability in semi-closed underwater rebreathing apparatuses. The tested rebreathers were RB80 (Halcyon dive systems, High springs, FL, USA), IS-Mix (Interspiro AB, Stockholm, Sweden), CRABE (Aqua Lung, Carros Cedex, France), and Viper+ (Cobham plc, Davenport, IA, USA). The tests were conducted using a catalytically based propene combusting metabolic simulator. The metabolic simulator connected to a breathing simulator, both placed inside a hyperbaric pressure chamber, was first tested to demonstrate its usefulness to simulate human respiration in a hyperbaric situation. Following this the metabolic simulator was shown to be a useful tool in accident investigations as well as to assess the impact of different engineering designs and physiological variables on the oxygen content in the gas delivered to the diver by the rebreathing apparatuses. A multi-compartment model of the oxygen fractions was developed and compared to the previously published single-compartment models. The root mean squared error (RMSE) of the multi-compartment model was smaller than the RMSE for the single-compartment model, showing its usefulness to estimate the impact of different designs and physiological variables on the inspired oxygen fraction. Keywords Diving, rebreather, underwater breathing apparatus, unmanned testing, hyperbaric, metabolic simulator, scuba, semi-closed vi List of appended papers The thesis is based on the following papers, which are referred to by their Roman numerals: Paper I FRÅNBERG O, Ericsson M, Larsson A, Lindholm P. (2011) Investigation of a demand-controlled rebreather in connection with a diving accident. Undersea Hyperb Med. 38(1):61-72. Paper II FRÅNBERG O, Loncar M, Larsson Å, Örnhagen H, Gennser M. (2014) A metabolic simulator for unmanned testing of breathing apparatuses in hyperbaric conditions. Aviat Space Environ Med. 85(11):1139-44. Paper III FRÅNBERG O and Gennser M. (2015) Measurement and modeling of oxygen content in a demand mass ratio injection rebreather. Undersea Hyperb Med. (in press) Paper IV FRÅNBERG O and Gennser M. (2015) Modeling a demand constant volume ratio exhaust and a self-mixing constant oxygen injection semi-closed rebreather. Submitted to IEEE Journal of Oceanic Engineering vii Table of content Abstract .................................................................................................................. vi Keywords................................................................................................................ vi List of appended papers ....................................................................................... vii Abbreviations .......................................................................................................... x Introduction ............................................................................................................. 1 The tested rebreathers ........................................................................................ 3 Nomenclature ...................................................................................................... 5 Theoretical models .............................................................................................. 6 Single compartment models ............................................................................ 6 Compartmentalized models ........................................................................... 10 Physiological variables ....................................................................................... 12 Respiration during diving ............................................................................... 12 Immersion ....................................................................................................... 13 Hydrostatic imbalance .................................................................................... 13 Pressure/density ............................................................................................. 13 Resistance ....................................................................................................... 13 Hyperoxia ........................................................................................................ 14 Dead space in the mouthpiece ........................................................................ 14 CO2 retainers and dive experience level ......................................................... 14 Oxygen consumption ...................................................................................... 15 Testing parameters ............................................................................................. 15 Aims ....................................................................................................................... 16 Method ................................................................................................................... 16 Choice of fuel ...................................................................................................... 19 Temperature in the catalyst .............................................................................. 20 Relative humidity .............................................................................................. 23 Calculation volume weighted average............................................................... 23 Results ................................................................................................................... 26 A diving accident (Paper I)................................................................................ 26 The metabolic simulator (Paper II) .................................................................. 27 Demand Mass Ratio Injection rebreather (Paper III) ...................................... 29 Demand Constant Volume Ratio Exhaust (Paper IV) ....................................... 31 Premixed Constant Mass injection and Self-Mixing Constant Oxygen Injection (Paper IV) .......................................................................................................... 32 Discussion ............................................................................................................. 35 viii Gas utilization.................................................................................................... 35 Self-Mixing Demand Controlled ....................................................................... 39 Future of SCR ..................................................................................................... 41 Methodological considerations ......................................................................... 42 Conclusions ........................................................................................................... 43 Acknowledgements ............................................................................................... 44 References ............................................................................................................. 46 ix Abbreviations ATP: ambient temperature and pressure [L] BTPS: body temperature and pressure, water saturated gas at 37°C [L] CMF/CMI: constant mass flow/injection CNS% fraction of the maximum allowed time at a specific oxygen partial pressure, are to be kept low to protect against effects of oxygen toxicity on the central nervous system D: diameter of outer bellows d: diameter of inner bellows DCVRE: demand constant volume ratio exhaust DCMRI: demand constant mass ration injection ECCR: electronic closed circuit rebreathing apparatus EVR: exhaust volume ratio similar to the 퐾푑 퐾푑: dosage ratio of ventilation ̇ 퐾푒: ventilatory equivalent 푅푀푉/푉푂2 퐹ℎ: oxygen fraction in the inhalation hose 퐹푚: oxygen fraction in the metabolic simulator or the alveolar gas in a diver 퐹푚푥: oxygen fraction in the feed gas 퐹푒푛푑 푡푑푎푙 oxygen fraction in the exhalation 퐹푛푠푝푟푒푑 inhaled oxygen fraction 퐹푂2 : inspired oxygen fraction 퐹푂2: oxygen fraction in a defined volume 푠푡푎푟푡 퐹표2 : initial or starting oxygen fraction 퐼푛푐푟푒푎푠푒 푝 퐹표2 oxygen fraction following a descent msw: meters of sea water OC: open circuit breathing apparatus 푃: pressure in ATA 푃푛푐푟푒푎푠푒 pressure increase in ATA 푄푑푙푙: diluent gas flow in to the loop 푄푚푥: fresh gas flow in to the loop 푄푂2: oxygen flow in to the loop ̇ ̇ 푅: respiratory exchange ratio푉퐶푂2/푉푂2from the ventilation 푅푓: respiratory frequency per minute 푅푀푉 minute
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