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The Marine Corps Systems Command documented mission requirements that cannot be met by current rebreathers. They need to extend dive times without compromising the stealth and compact design of existing devices. This can be accomplished by reducing the fresh gas flow rate. The current flow rate is adequate to support a diver in heavy work. However, the diver will be utilizing a Diver Propulsion Device (DPD) during a large portion of the mission in question. The assumption, then, is that this portion of the mission will not require "hard work". Thus, a new fresh gas flow rate can be established which is sufficient to sustain a Marine diver using a DPD but is conservative enough to extend the duration of the dive. This experiment was designed for manned testing of the rebreathers in such a way to establish the average oxygen consumption rate for divers using a DPD. Marine divers were fitted with a Divex Shadow Excursion (DSE) rebreather modified with a Draeger C8A PO2 monitor coupled with a Delta P VR3 dive computer. The DSE is a semiclosed-circuit underwater breathing apparatus that provides a constant flow of mixed gas containing oxygen and nitrogen or helium to the diver. The partial pressure of oxygen (PO2) and diver depth were monitored and recorded at ten-second intervals. The Navy Experimental Diving Unit has developed and tested a computational algorithm that uses the PO2 and depth to compute the oxygen consumption rate. Two techniques were employed to estimate the error in this approach: curve fitting and propagation of error. These methods are detailed and the results are presented. They show that the fresh gas flow rate can be safely reduced while the diver is utilizing the DPD, which consequently, will substantially increase the dive time allowed by the device.

A self-contained self-rescue unit is a device that is used in the mining industry in case of fires or release of toxic gases that depletes or contaminates breathable oxygen in the surrounding atmosphere. These units are the first line of defense by providing oxygen in a closed breathing cycle, allowing personnel to get themselves to safety. The goal of this project was to design a unit that is more comfortable to carry during the daily operations in and outside the mines. A unit that is easier to done and less likely to damage the users and/or surrounding mining equipment. It is developed in close collaboration with Atlas Copco, as the main sponsor, as well as Dräger and personnel working at Zink Gruvan Mining.  The result is a unit with an operational time of twenty minutes and a reduced size and weight. It’s position can be adjusted to be worn around the waist or the chest, depending on the tasks the user performs, as well as simplifying the donning procedure.

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. / <p>QC 20150903</p>

When scuba diving under a physical overhead such as a cave, a mine, a shipwreck, or under a virtual overhead due to decompression requirements, it makes it impossible to safely access the surface in the event of an emergency. Therefore, diving with overhead is often described as technical diving. In this research, I address how technical divers in Outaouais, Quebec, practice this risky sport with unforgiving consequences. Based on fieldwork in Outaouais, I focus on divers, including myself, who perform trimix dives deeper than 200 feet. I argue that the process of becoming a deep diver is a lifelong journey where a diver learns to adapt to a milieu hostile to human life. The basic skills are acquired during classes to ensure that a novice diver will survive in this limit-environment. As divers bend the rules and take more risks to go deeper for longer lengths of time, they will go through a series of limit-experiences and near misses that are essential to their development and found to be regenerative. In turn, those limit-experiences and near-miss events shared with teammates create mutual trust. It is this trust that becomes the foundation of the team and allows the team to improve upon existing techniques and increase the depth and difficulty of their dives.

Vital components are more or less prone to fail in a diving apparatus. This thesis examines the performance of oxygen sensors, carbon dioxide scrubber monitoring and composite gas cylinders. A partial pressure of oxygen sensor authentication is suggested in a published patent and poster, weaknesses in carbon dioxide scrubber monitoring systems near surface are revealed in a published paper and potential harmful gas permeability properties of a composite gas cylinder, altering the gas composition and decreases the oxygen fraction, is measured and determined in a submitted paper.The importance of adequately and thoroughly performed safety tests that are standardized becomes even more relevant when managing personal protective equipment. The European Committee for Standardization have ratified relevant standard for the work in this thesis;EN-14143 Respiratory equipment – Self-contained re-breathing diving apparatus,EN-12245:2009+A1:2011 Transportable gas cylinders – Fully wrapped composite cylinders, andISO 11119-3:2013 Gas cylinders – Refillable composite gas cylinders and tubes – Design, construction and testing.These tests form a base-line for the methods, tests and result evaluations performed here and are considered safe; however improvements to the tests and standards can be made and are here suggested.