IEC 61508 Safety Case: Design Validation


Design Validation (DV) and Verification Reports on Open Safety Equipment Ltd's Rebreathers.

Open Safety produce and support its range of rebreathers, within Deep Life Group's certified Functional Safety processes. Design and validation is performed by other companies within Deep Life Group to avoid conflicts of interest - the principle that the designer does not test, and the testing is not performed by the same team that manufacturers or sells the product.

All reports reported here has been subject to completely independent audit (by SGS as the Notified Body, Qinetiq, or SIRA), and by an industry panel assembled from outside Deep Life Group. Our advanced technologies such as end-of-tidal CO2 sensing, twin scrubbers, and umbilical rebreather were subject to a Devils Advocate review by a lead competitor contracted for that purpose. Our publication here implements the Functional Safety "Right to Know" for all safety data. Additionally it extends that level of critical review to include the public and all other interested parties.


Respiratory performance of ALVBOV in Open Circuit mode (0.5 MB)
EN 250 respiratory performance measurements of the ALVBOV with Apeks and Apollo first stage regulators, and comparison with the Apeks TX100 as the industry performance benchmark. European limit for WOB is 2.5J/L in EN 250:2000, and 3J/L in Appendix A1:2006. Measured WOB for the ALVBOV is 0.89 J/L, similar to the benchmark.

Breathable Volume of O.R. Umbilical, Incursion and Apocalypse Rebreathers with compliance to EN 14143:2003 (1.1MB)
Reports key test results, to ensure the breathing volume is accessible by the diver in all positions, and is sufficient.

Work of Breathing and Breathing Resistance Compliance of O.R. Umbilical, Incursion and Apocalypse Rebreathers (5.4 MB)
Updated November 2010: This is a comprehensive treatise on the theory and practice of work of breathing and breathing resistance measurements for compliance purposes. It provides data for all Deep Life rebreathers for all diving depths, and rebreather mouthpieces, with contemporary benchmarks.

Hydrostatic imbalance of Deep Life Open Revolution Rebreathers: compliance assessment to EN 14143, NORSOK U101, NATO STANAG 1410 and NEDU TA05-12 requirements (3.9MB)
Updated 16th Nov 2010. Full test using production samples to design documentation revision in Bill Of Materials Rev 20. Format and procedure follows that of hydrostatic tests on previous versions of these products, but with complete retest.


Oxygen Cells for Dive Applications: Sourcing, Performance, Safety and Reliability. (4MB)
Last updated 15th April 2016. Characterisation of galvanic oxygen cells, including failure modes and mitigating actions required to use oxygen sensors safely in rebreather applications.

Oxygen Cell Failure Test Cases for Assessment of PPO2 Sensor Fusion and PPO2 Control Algorithms (362KB)
Last updated 25th March 2013. Test cases for use in validating the safety of PPO2 sensor fusion algorithms and PPO2 Controllers prior to lab testing

CNS Oxygen Toxicity Algorithm and Verification (385KB)

Last updated 15th November 2013. CNS O2 Toxicity computation for rebreather and dive computer use, including formal model and implementation in SPARK Ada.

Tolerance of Deep Life Oxygen Cells to CO2 Exposure (528KB)
An assessment of the effect of CO2 exposure on the performance of oxygen cells for rebreather applications.

PPO2 Accuracy (1.5M)
Updated 5th Jan 2011. Verification Report on the accuracy of the oxygen readings, including the sensor compensation, used in the Open Revolution rebreathers, and operation of the active warning devices.



SFA3 Oxygen Sensor Fusion Algorithm, 25th June 2012 (1.3MB)
Failure analysis shows that voting algorithms are unsafe with oxygen sensors, due to their prevalence for failing in the same state. A sensor fusion algorithm, SFA3, provides a safe solution for combining oxygen sensor values, for critical applications such as PPO2 control in rebreathers. The algorithm and its verificiation is summarised in this report.

Verification of Fail Safe Oxygen Dosing System in an eCCR (1.6MB)
Updated 16th Aug 2010. Verification of the fail safety of the PPO2 control system, including both formal modelling and the results of empiral tests. The results are relevant to mCCRs, needle valve CCRs and SCRs, as well as true electronic variable orifice injectors.

Verification of Variable Orifice Gas Injector Rev A (1.68MB)
Updated 2nd Mar 2007. This is the test and verification report on the Deep Life rebreather Gas Injector. It contains the orifice and control model used to verify the operation of orifice based injectors. A further report will be issued on the first production batch incorporating the modifications described.

Open Revolution single scrubber endurance to EN14143 and NORSOK U101 and Volume Weighted Average Inspired CO2 during endurance tests. (1.6MB)
Scrubber performance of the single scrubber Open Revolution rebreathers, December 2010.

Respiratory Rate Sensing (840KB)
Disclosure and verification of the respiratory rate sensor used in the O.R. rebreathers, as both a safety monitor for some hypercapnia risks and in compensating CO2 sensors. Release 30th Nov 2010.

Power Systems 1: Saphion IFR18650e Li-Ion Cell Characterisation (1024KB)
Verification of the suitability of Valence Saphion IFR 18650e rechargeable Li-Ion cells for diving rebreathers, including the charge and discharge characteristics and the accuracy of Deep Life's battery life prediction algorithm when used with these cells.

Power Systems 2: Rebreather Power Supplies (312KB)
Verification and review of the power supplies in the Deep Life O.R. rebreather. This is report 2 of 4 on the O.R. rebreather power systems.
Report 3 of 4 is the brown out, drop out, over-voltage and watchdog functions, and is currently part of Volume 5 of the FMECA but will be split out shortly.

Deep Life Open Revolution Product: Commercial Diving Rebreather design verification report: safety of umbilical terminator power systems under fault conditions (482KB)
Review and validation of power supplies in the Umbilical Terminator fitted to the rebreather for commercial diving applications. Report 4 of 4.

Pressure Gauge Maximum Depth Test (0.2 MB)
EN 250 approval of pressure gauges covers their use only to depths of 50m. All Open Revolution rebreathers use Megasport pressure gauges where an analogue gauge is required. This report describes the test of Megasport gauges and their rating for use to 550m.
Other Sensors

Accuracy in service of rebreather helium sensor(470KB)
Accuracy assessment of helium sensor, as a function of ageing, pressure, temperature and power supplies. September 2009.

Helium and Pressure Susceptibility of Components used in Electronic Systems (686KB)
Updated 16th Aug 2010. A screen of different generic types of electronic components for sensitivity to helium under pressure.

Safety Review of Rebreather Test Processes (8.6MB)
This considers the overall safety of the test and verification programme, concentrating on test chambers.