Section 4 Oxygen Safety in Diving Systems
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Construction & Classification of Submersibles & Diving Systems, July 2022 - Part 5 Main and Auxiliary Machinery, Systems and Equipment - Chapter 3 Piping Systems - Section 4 Oxygen Safety in Diving Systems

Section 4 Oxygen Safety in Diving Systems

Parent topic: Chapter 3 Piping Systems

4.1 General Safety Requirements

4.1.1 Fires have occurred when using high-pressure oxygen in diving operations. These have happened mainly when high-pressure oxygen has been opened up onto unpressurised lines. This has resulted in either explosions or localised fires. The majority of these incidents are caused by a combination of contaminated oxygen systems or the use of materials in the oxygen systems which are incompatible with oxygen and isentropic heating caused by too rapid pressurisation of the lines.

4.1.2 It is also important to note that if polytetrafluoroethylene (PTFE) reaches a high enough temperature it creates phosgene gas, which is lethal.

4.1.3 The following points should be considered when designing and using oxygen supplies in diving systems:
  1. Reduce high-pressure oxygen to low-pressure (40 bar, maximum) at the main supply quad.
  2. Avoid long runs of flexible hose.
  3. All materials and fittings should be oxygen compatible.
  4. Avoid ball valves in high-pressure systems.
  5. Avoid sharp bends in oxygen piping.
  6. All oxygen piping connections and oxygen supply connections on storage cylinders should be blanked when not in use.

4.1.4 All diving breathing mixtures should be checked on receipt and re-checked immediately prior to connecting them to a diving gas supply or breathing apparatus charging system.

4.1.5 When using commercially supplied air quads, nitrox mixes and pure oxygen, it is recommended that oxygen analysers, fitted with audio and visual Hi-Lo alarms, are provided for surface supplied diving operations. To ensure the accuracy of the analysis, the sample point should be taken downstream of the dive control panel and immediately prior to the diver’s umbilical. The design must allow for simple safe analysis of any gas being supplied to the diving system including its gas storage banks.

4.1.6 Metallic materials wetted by oxygen shall not propagate a flame, shall not burn, and shall be impact resistant with oxygen at the maximum operating pressure of the system in accordance with ASTM G94, Standard Guide for Evaluation Metals for Oxygen Service. Non-metallic material wetted by oxygen shall be resistant to impact ignition, and shall have the lowest possible heat of combustion in accordance with ASTM G63, Standard Guide for Evaluating Non-Metallic Materials for oxygen Service. Additionally, where non-metallic material is utilised in, the design shall minimise the surface area and volume exposed to oxygen.

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