The safety relevance of standardized tests for diving equipment

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 safety relevance of standardized tests for diving equipment

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

Surviving under water : Physiological limitations and technical possibilities

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

Surviving under water : Physiological limitations and technical possibilities

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

Permeability properties of a pressure induced compacted polymer liner in gas cylinder

The permeability properties of composite gas cylinders for breathing gas with polymer inner-liner are investigated. The cylinder wall can be described as a composite membrane consisting of two layers. The permeability properties of the cylinder are presented as permeability coefficient and permselectivity. Deviation from the expected gas components might lead to incidents and potentially harmful situations when breathing gas from a compressed gas cylinder. Hence, gas permeability and potential changes in gas composition, must be considered when choosing cylinder materials. Cases of decompression sickness initiated this study. Experimental data show that pressure and oxygen fraction in the gas cylinder drops and that the permeability coefficient varies depending on the inner pressure. Permeability coefficients of 0.62–0.90 Barrer for oxygen and 0.44–0.56 Barrer for nitrogen are measured. Cracks in the inner-liner have caused an accentuated drop in of oxygen fraction and pressure. © 2020 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals LLC.open access</p

Safety algorithm for predicting PO2 in electronic closed circuit rebreathers

Poster at UHMS Annual Scientific Meeting 2016</p

Proposed Thalmann algorithm air diving decompression table for the Swedish Armed Forces

The Swedish Armed Forces (SwAF) air dive tables are under revision. Currently, the air dive table from the U.S. Navy (USN) Diving Manual (DM) Rev. 6 is used with an msw-to-fsw conversion. Since 2017, the USN has been diving according to USN DM rev. 7, which incorporates updated air dive tables derived from the Thalmann Exponential Linear Decompression Algorithm (EL-DCM) with VVAL79 parameters. The SwAF decided to replicate and analyze the USN table development methodology before revising their current tables. The ambition was to potentially find a table that correlates with the desired risk of decompression sickness. New compartmental parameters for the EL-DCM algorithm, called SWEN21B, were developed by applying maximum likelihood methods on 2,953 scientifically controlled direct ascent air dives with known outcomes of decompression sickness (DCS). The targeted probability of DCS for direct ascent air dives was ≤1% overall and ≤1‰ for neurological DCS (CNS-DCS). One hundred fifty-four wet validation dives were performed with air between 18 to 57 msw. Both direct ascent and decompression stop dives were conducted, resulting in incidences of two joint pain DCS (18 msw/59 minutes), one leg numbness CNS-DCS (51 msw/10 minutes with deco-stop), and nine marginal DCS cases, such as rashes and itching. A total of three DCS incidences, including one CNS-DCS, yield a predicted risk level (95% confidence interval) of 0.4-5.6% for DCS and 0.0-3.6% for CNS-DCS. Two out of three divers with DCS had patent foramen ovale. The SWEN21 table is recommended for the SwAF for air diving as it, after results from validation dives, suggests being within the desired risk levels for DCS and CNS-DCS

The performance of 'temperature stick' carbon dioxide absorbent monitors in diving rebreathers

INTRODUCTION: Diving rebreathers use canisters containing soda lime to remove carbon dioxide (CO2) from expired gas. Soda lime has a finite ability to absorb CO₂. Temperature sticks monitor the exothermic reaction between CO₂ and soda lime to predict remaining absorptive capacity. The accuracy of these predictions was investigated in two rebreathers that utilise temperature sticks. METHODS: Inspiration and rEvo rebreathers filled with new soda lime were immersed in water at 19°C and operated on mechanical circuits whose ventilation and CO₂-addition parameters simulated dives involving either moderate exercise (6 MET) throughout (mod-ex), or 90 minutes of 6 MET exercise followed by 2 MET exercise (low-ex) until breakthrough (inspired PCO₂ [PiCO₂] = 1 kPa). Simulated dives were conducted at surface pressure (sea-level) (low-ex: Inspiration, n = 5; rEvo, n = 5; mod-ex: Inspiration, n = 7, rEvo, n = 5) and at 3-6 metres' sea water (msw) depth (mod-ex protocol only: Inspiration, n = 8; rEvo, n = 5). RESULTS: Operated at surface pressure, both rebreathers warned appropriately in four of five low-ex tests but failed to do so in the 12 mod-ex tests. At 3-6 msw depth, warnings preceded breakthrough in 11 of 13 mod-ex tests. The rEvo warned conservatively in all five tests (approximately 60 minutes prior). Inspiration warnings immediately preceded breakthrough in six of eight tests, but were marginally late in one test and 13 minutes late in another. CONCLUSION: When operated at even shallow depth, temperature sticks provided timely warning of significant CO₂ breakthrough in the scenarios examined. They are much less accurate during simulated exercise at surface pressure. Copyright: This article is the copyright of the authors who grant Diving and Hyperbaric Medicine a non-exclusive licence to publish the article in electronic and other forms