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.

The survival of humans in underwater environments necessitates a comprehensive understanding of both physiological factors and advanced technologies. Diving with self-contained underwater breathing apparatuses (SCUBA) remains one of the most common ways for human underwater activities. This thesis explores the challenges of surviving underwater by investigating diving equipment performance and human physiological modeling from both a deterministic and statistical perspective.

The research examines the change of gas composition when storing nitrox gas in a composite gas cylinder over extended periods, up to one year. This analysis aims to better understand the implications of long-term storage on gas properties and safety.

The efficacy of a signal analysis software algorithm designed to ascertain the accuracy of electronic rebreather oxygen sensors is evaluated. The algorithm's purpose is to provide enhanced safety measures for oxygen sensors integrated into various closed-circuit rebreathers, pursuing reliable data.

The reliability of temperature monitoring of carbon dioxide scrubbers is investigated as a method to predict remaining carbon dioxide absorption capacity. This temperature monitoring acts as a crucial "fuel gauge," contributing to diver safety by preventing potential risks associated with scrubber material depletion.

The research seeks to explore the principles and methodologies that can be employed to optimize the decompression algorithm, with the purpose of enhancing diver safety during decompression procedures. By employing probabilistic modeling techniques, the research aims to propose innovative solutions to minimize the risk of decompression sickness, contributing to advancements in underwater safety practices.

Additionally, the thesis explores the possibilities of altering the oxygen breathing regimen for the Inside Attendant during long-duration hyperbaric oxygen therapy (HBOT) to facilitate rapid decompression without compromising safety.