EFFECT OF SMALL VARIATIONS IN TEST CONDITIONS ON …deeplife.co.uk/or_files/DV_OR_ScrubberEndurance_081124.pdf · EFFECT OF SMALL VARIATIONS IN TEST CONDITIONS ON THE CO2 SCRUBBER

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DV_OR_ScrubberEndurance_081124.doc Rev C Page 1 of 41

DL OPEN REVOLUTION REBREATHER FAMILY OF PRODUCTS

EFFECT OF SMALL VARIATIONS IN TEST CONDITIONS ON THE CO2

SCRUBBER ENDURANCE TO EN14143:2003 AND NORSOK U-101

DOCUMENT NUMBER:[Filename]

DV_OR_ScrubberEndurance_081124.doc

CONTRIBUTORS: Dr. Bob Davidov, Dr. Oleg Zagrebelny, Mihael Soloviev, Viktor Sudakov, Dr. Alex Deas

DEPARTMENT: Engineering LAST REVISED: 24th Nov 2008

REVISION: C

APPROVALS _______________________________ Project Manager

________________________Date

_______________________________ Quality Officer

________________________Date

Controlled Document Classified Document DO NOT COPY.

Revision History Revision Date Description

A1 5th May 2008 Document assembled from other files

B 5th May 2008 Calibration information moved to DV report

C 24th Nov 2008 Horizontal cases added. Correlation with results at Micropore facility.

Copyright © 2008 Deep Life Ltd

All patents, patent applications, design and topographical rights reserved. No circuit may be reproduced without a licence for the topographical rights contained therein from Deep Life Ltd.

This document does not constitute a licence to use and patent, patent application or topographical right of Deep Life Ltd.

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Table of Contents1 PURPOSE AND SCOPE...........................................................................................3

2 TEST STRUCTURE AND PARAMETERS................................................................3

3 CALIBRATION AND EQUIPMENT...........................................................................8

4 TEST RESULTS........................................................................................................9

4.1 Standard conditions: Vertical, Gas temperature 32C, water 4C ................................................ 9

4.2 Colder water: Vertical, 32C exhale, but ambient water just 1C, test 3 scrubbers .................. 13 4.2.1 First scrubber sample ............................................................................................................... 13 4.2.2 Second scrubber sample ........................................................................................................... 16 4.2.3 Third scrubber sample.............................................................................................................. 20

4.3 Colder water: Vertical, 32C exhale, but ambient water just 1C, short interrupt of CO2 injection ..................................................................................................................................................... 22

4.4 Effect of using a scrubber for two dives in very cold conditions............................................... 24

4.5 Reducing the exhaled gas temperature from 32C to 21C .......................................................... 28

4.6 Horizontal Position: 32C exhale, 1C water, test three scrubbers.............................................. 31 4.6.1 First scrubber cartridge sample ................................................................................................ 32 4.6.2 Second scrubber sample ........................................................................................................... 35 4.6.3 Third scrubber sample.............................................................................................................. 37

5 MAXIMUM INHALED CO2 LIMITS .........................................................................38

6 CORRELATION WITH THIRD PARTY TEST RESULTS .......................................38

7 CONCLUSION ........................................................................................................39

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1 PURPOSE AND SCOPE This document describes the test method and results of scrubber endurance trials carried out by Deep Life Limited to assess the effect of small variations in temperature on the scrubber endurance. The variations considered are:

1. Reference test under standard conditions defined in EN14143 and NORSOK U-101

2. Effect of reducing the ambient water temperature from 4C to 1C

3. Effect of reducing the exhaled gas temperature from 32C to 21C

4. Effect of performing two dives with an interval of 18 hours without changing the scrubber rotation, and assuming the dives have a low exhaled gas temperature.

5. Effect of adopting a horizontal position instead of a vertical position in very cold ambient water (1C)

All tests were done at 40msw, using the 1.6 lpm flow rate specified as one of the tests in NORSOK U-101 and the only test condition in EN14143:2003.

Tests were stopped at a PPCO2 corrected to surface pressure of at least 2kPa: the NORSOK U-101 maximum permitted CO2 level, to ensure the curve is gradual and continuous. DL generally rate scrubbers to the 2kPa limit permitted in NORSOK U-101, as this limit is free of symptoms for normal diving over the short duration this spike occurs.

The scrubbers are tested inside the single scrubber Open Revolution rebreather (Sample 1).

2 TEST STRUCTURE AND PARAMETERS The tests use the following equipment:

1. Single scrubber Open Revolution rebreather, fitted with scrubber health monitor (12 temperatures measured axially along the scrubber) and RH sensor immediately prior to scrubber.

2. Deep Life Breathing Machine A, fitted with humidifier

3. Matlab data capture system.

4. 600mm diameter chamber working pressure to 2000msw, with refrigeration

5. 160mm diameter chamber rated to 300msw for calibration purposes.

6. Chamber refrigeration cooling system, computer controlled.

7. Supply of compressed gases including air, pure carbon dioxide and nitrogen.

8. Pressure, CO2, temperature and humidity sensors

9. Mass flow control valve

10. Fresh Micropore EAC scrubbers are required for each test run. The scrubbers were the 125mm Micropore EACs, with large internal bore, of a batch marked “Use by February 2009”.

11. Scales to weigh the CO2 cylinder before and after each test to confirm that the correct amount of CO2 is injected. The smallest cylinder that can provide sufficient CO2 for the test is a 10 litre cylinder for a single cartridge: the test requires 9.1 litre calculated as (1.6lpm_of_MR x (150min_of_test+50_min_of_reserve)) / (45bar_of_start_pressure – 10bar_of_end_pressure). The weight of a 10 litre cylinder is 15 kg. The weight of the gas used for the 150 min test is 473 g (as 1.6l/m x 150

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min x 1.97 g/l). This check is only a gross check: it is not a calibration check because it would require a balance with 20 kg range and 5g or 0.025% accuracy to measure the amount of CO2 weigh with 1% accuracy.

Note: the pressure of the remaining CO2 is monitored, with correction for temperature. The maximum pressure of CO2 against temperature is shown in Figure 2-1. This plot is derived from the CO2 pressure – temperature phase diagram shown in Figure 2-2

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Figure 2-1. Gas – liquid phase diagram of CO2 (detail).

Figure 2-2. Gas – liquid phase diagram of CO2.

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The CE EN14143:2003 and the comparable NORSOK U-101 test, specify the following test conditions:

1. Depth/ambient pressure is 40 msw / 5 bar

2. Water temperature is 4+/-1C or less

3. Diluent gas is Nitrogen

4. Carbon dioxide injection rate is 1.6 lpm

5. Breathing simulator rate is 40 lpm

6. Breathing frequency is 20 min-1

As for EN14143:2003, NORSOK U-101 the scrubber endurance is stated for the PPCO2 being less than 5 mbar shown in Figure 2-3 and less than the warning levels of 8 mbar and 20 mbar shown in Figure 2-4.

5

EnduranceTime

PPCO2,mbar

Figure 2-3. Scrubber endurance as defined in EN14143:2003. The 0.5 kPa is a very low level. DL generally uses the NORSOK limits which are compared below.

PPCO2

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EN14143:2003 NORSOK U-101

Warning level:< 20 mbar(< 2 kPa)

Figure 2-4. PPCO2 warning levels for EN14143 and NORSOK U-101.

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Exhale flow is separated from the breathing cycle by sampling the gas line at the diver’s lips (using a dummy mouthpiece bite), and switching it using a solenoid which is open during exhale cycles. The exhale cycle is synchronized with the breathing machine without any delay.

Before testing the mass flow control valve used for CO2 injection has been set for 1.6 lpm flow rate under the valve input pressure of 10 bar, which has been calibrated: a DV report is available. A flow metre provides a further measure to monitor flow levels.

The test fixture used for scrubber endurance tests is shown in Figure 2-5.

All operations of the test fixture other than connecting gases, are computer controlled and logged.

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N2

cylin

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Figure 2-5. Deep Life’s scrubber endurance test fixture.

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3 CALIBRATION AND EQUIPMENT The calibration of the response of the CO2 sensor was a complex process, as it involved confirming that it can provide a 150ms response. Due to the extensive nature of those calibrations, a detailed calibration report and equipment description has been produced for these tests, in DV_CO2_Cal_081201.pdf This report is summarised below.

This calibration process forms the bulk of the separate calibration report. It is noted that the mixing that occurs in the sampling line will reduce the effective response time.

The calibration of the instruments used in the tests are managed within the normal QA controls, except for the flow and CO2 sensors, which are critical to the scrubber endurance tests, so is quad checked using the process describe below and then further audited using a fifth method, as well as having tests carried out at an independent laboratory.

The volume of CO2 injected from the cylinder is verified by the use of four methods (that is, by using all four methods each time to ensure there is no significant error):

1. By the change in the weight of the CO2 cylinder,

2. By the cylinder pressure. As a reference the temperature of CO2 inside the cylinder is calculated using the measured pressure and the pressure-temperature phase diagram shown in Figure 2-1.

3. By oxygen trace gases. The CO2 is mixed with air, such that a bleed measurement gas can be taken from the device under test without reducing the pressure in the chamber. The bleed causes a reduction in PPO2 which should be compensated almost exactly by the injected O2, if the injection rate is correct. To check this, the PPO2 of the loop is monitored. The flow from the bleed line is monitored: this should be between 0.08 and 0.2 lpm.

4. By the period during which there is a CO2 flow at a constant rate: this is the primary method used to set the amount of CO2 dosed into the scrubber. The accuracy this method depends on the accuracy of the CO2 flow through the mass flow controller. The controller is calibrated using a 1.6 lpm test flow at STPD (273ºK, i.e. 0ºC, and 1 atm). At room temperature a temperature correction must be used as shown in Figure 3-1.

Figure 3-1. CO2 flow calibration.

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The flow sensor output is checked by filling a known volume with gas, by displacement of water. The flow rate is proportional to the change in volume over a fixed time interval.

The calibration of the flow sensor found it had a different reading if vertical compared to horizontal. It was calibrated in the position used for the appropriate test. Calibration data is held on SVN.

A post-test audit was carried out by requesting the reading from the CO2 sensor immediately prior to the scrubber, and confirming that the sum of the inhaled PPCO2 and the injected PPCO2 is shown on that sensor. All sensor data was stored for the entire sequence of these tests.

4 TEST RESULTS

4.1 Standard conditions: Vertical, Gas temperature 32C, water 4C The power of the breathing gas heating was set to 108W as 34V^2/11ohm ..(35V^2/11ohm)*97%, to achieve an exhaled gas temperature of 32C. During the temperature stabilisation period of 50 minutes, the power was 106W.

The test includes the following steps.

1. Run Re-Br 2. Close chamber 3. Fill chamber via the breathing loop by air up to 5 bar absolute pressure (40 msw) 4. Apply CO2 of 1.6 lpm via the mass control valve to BM 5. Open CO2 measuring channel to set the flow rate of ~0.16 lpm. Flow is checked

using the flow sensor 6. Apply the external air flow into the breathing loop to compensate the gas flows from

the breathing loop into the CO2 measuring channel. 7. Testing until measured CO2 surface corrected, exceeds 4% 8. Stop Re-Br 9. Stop CO2 injection. 10. Decrease chamber pressure down to atmospheric pressure. 11. Stop test data recording. 12. Open chamber

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Figure 4-1. Ambient pressure against time.

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Figure 4-2. . CO2 in the breathing loop against time. SCRB time life (2mbar PPCO2) = 77 min; SCRB time life (5mbar PPCO2) = 108 min or 1 hour 48 min; SCRB time life (20mbar PPCO2) = 165 min or 2 hour 45 min;

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Figure 4-3. Temperature water, heater, and inside BM.

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Figure 4-4. Temperature in rebreather and scrubber stick.

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Humidity inside the membrane bell against Time

Humidity immediately prior to the scrubber.

Figure 4-5. Humidity in the breathing machine and the rebreather against time. The

average humidity in the breathing machine is 55%.

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Figure 4-6. Gas flow from the breathing loop exhale into the CO2 measuring

channel against time.

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4.2 Colder water: Vertical, 32C exhale, but ambient water just 1C, test 3 scrubbers The exhale gas temperature was set to 32C (power to the breathing gas heating was set to 110W as 35V^2/11ohm*99). The water was cooled to 1C - there was some lag at the start of the test. Three scrubber samples were tested.


1. Run Re-Br 2. Close chamber 3. Fill chamber via the breathing loop by air up to 5 bar absolute pressure (approx 40

msw) 4. Apply CO2 of 1.6 lpm via the mass control valve to BM 5. Open CO2 measuring channel to set the flow rate of ~0.16 lpm. Flow is checked

using the flow sensor. 6. Apply the external air flow into the breathing loop to compensate the gas flows from

the breathing loop into the CO2 measuring channel. 7. Testing until measured CO2 surface corrected, exceeds 4% 8. Stop Re-Br 9. Stop CO2 injection. 10. Decrease chamber pressure down to atmospheric pressure. 11. Stop test data recording. 12. Open chamber

4.2.1 First scrubber sample

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Figure 4-8. . CO2 in the breathing loop against time. SCRB time life (2mbar PPCO2) = 58 min; SCRB time life (5mbar PPCO2) = 83 min or 1 hour 23 min; SCRB time life (20mbar PPCO2) = 144 min or 2 hour 24 min;

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Figure 4-9. Temperature water, heater, and inside B

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Figure 4-11. Humidity in the breathing machine and the rebreather against time. The average humidity in the breathing machine during the scrubber endurance is

75%.

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4.2.2 Second scrubber sample Note: The test is terminated on this run when the CO2 reaches gets 5.5 mbar.

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Figure 4-14. . CO2 in the breathing loop against time. CO2 injection starts at 25.5 min SCRB time life (2mbar PPCO2) = 63 min or 1 hour 3 min; SCRB time life (5mbar PPCO2) = 104 min or 1 hour 44 min;

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Humidity inside the membrane bell (~91%).

Figure 4-17. Humidity in the breathing machine (~71%) and the rebreather against

time.

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4.2.3 Third scrubber sample

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Figure 4-20. . CO2 in the breathing loop against time. CO2 injection starts at 24 min SCRB time life (2mbar PPCO2) = 61 min or 1 hour 1 min; SCRB time life (5mbar PPCO2) = 96 min or 1 hour 36 min; SCRB time life (20mbar PPCO2) = 188 min or 3 hour 8 min;

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4.3 Colder water: Vertical, 32C exhale, but ambient water just 1C, short interrupt of CO2 injection The CO2 injection is interrupted at 167 min for 4 min to calibrate the CO2 response in measurement channel.

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Figure 4-23. . CO2 in the breathing loop against time. CO2 injection starts at 8 min SCRB time life (2mbar PPCO2) = 47 min; SCRB time life (5mbar PPCO2) = 77 min or 1 hour 17 min; SCRB time life (20mbar PPCO2) = 192 min or 3 hour 128 min;

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Figure 4-24. Temperature water, heater, and inside BM

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Figure 4-26. Humidity in the breathing machine (~71%) and the rebreather against

time.

4.4 Effect of using a scrubber for two dives in very cold conditions This test considered the effects of two ice dives, in very cold conditions.

From other testing, DL know that interrupting the test seems to extend the scrubber life. This is particularly the case if the scrubber is rotated about its axis by 180 degrees. This test in cold conditions did not rotate the scrubber, but simply ran two dives with an 18 hour interval between them.

To recreate the worst possible diving conditions, the exhale gas temperature was reduced from the usual 32C to 7C for the first dive, and 13C for the second dive.

During the first stage air is used as a diluent gas, the heater of the exhale gas is off.

During the second stage the pure nitrogen fills the breathing loop to compensate the ambient pressure, the heater of the exhale gas is on. The power of the breathing gas heating is 26W as 24V^2/11ohm/2 to achieve 13C.

The first stage of the test includes the following steps.



the breathing loop into the CO2 measuring channel. 7. Testing in one hour 8. Stop Re-Br 9. Stop CO2 flow input into the rebreather 10. Decrease chamber pressure down to atmospheric pressure. 11. Stop test data recording.

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12. Open chamber

The second stage steps are

13. Run Re-Br 14. Close chamber 15. Fill chamber via the breathing loop by N2 up to 5 bar absolute pressure (40 msw) 16. Apply CO2 of 1.6 lpm via Porter flow controller to BM 17. Open CO2 measuring channel with flow rate of ~0.16 lpm. Flow is checked using the

flow sensor 18. Apply external N2 flow into the breathing loop to compensate flow into the CO2

measuring channel. 19. Testing until CO2 in the measuring channel exceeds 4%, surface corrected 20. Stop CO2 injected into the breathing loop 21. Drop the chamber pressure down to the atmospheric pressure 22. Stop Re-Br 23. Stop test data recording. 24. Open chamber

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Figure 4-28. .Second stage of the test. CO2 in the breathing loop against time.

Reminding the scrubber endurance during the first stage of the test SCRB time life (2mbar PPCO2) = 59 min; SCRB time life (5mbar PPCO2) = 91 min or 1 hour 31

min; SCRB time life (20mbar PPCO2) = 130.5 min or 2 hour 10.5 min;

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Figure 4-29. PPO2 in the breathing loop

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Figure 4-32. Humidity in the rebreather. The humidity is below 80% for the beginning of the dive because the gas temperature is below the dew point.

4.5 Reducing the exhaled gas temperature from 32C to 21C The power of the breathing gas heating was set to 52W (24V^2/11ohm), to achieve a desired breathing gas temperature of 21C. This is to assess the effect of additional gas cooling from the diver, due to longer hoses, narrower hoses or stainless steel hoses.




the breathing loop into the CO2 measuring channel. 7. Testing until CO2 in the breathing loop exceeds 4%, surface corrected 8. Stop Re-Br 9. Stop injection of CO2. 10. Decrease chamber pressure down to atmospheric pressure. 11. Stop test data recording. 12. Open chamber

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Figure 4-34. . CO2 in the breathing loop against time. SCRB time life (2mbar PPCO2) = 42 min; SCRB time life (5mbar PPCO2) = 69.3 min or 1 hour 9.3 min; SCRB time life (20mbar PPCO2) = 108.7 min or 1 hour 48.7 min;

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Figure 4-37. Humidity in rebreather against time, measured immediately prior to the

scrubber.

4.6 Horizontal Position: 32C exhale, 1C water, test three scrubbers

The horizontal position was tested using three scrubbers, under as similar conditions as could be achieved in a reasonable time, to assess the effect of a horizontal attitude in the worst case diving conditions.

The test depth and CO2 flow rate was otherwise set to be the same as for the test of the rebreather in the vertical position in 1C ambient water, with 32C exhale temperature.

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4.6.1 First scrubber cartridge sample

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Figure 4-39. . CO2 in the breathing loop against time. CO2 injection starts at 16 min. SCRB time life (2mbar PPCO2) = 54 min; SCRB time life (5mbar PPCO2) = 90 min or 1 hour 30 min; SCRB time life (20mbar PPCO2) = 169 min or 2 hour 49 min;

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Figure 4-42. Humidity in the breathing machine and the rebreather against time..

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Figure 4-43. Gas flow from the breathing loop exhale into the CO2 measuring channel against time: this is the measurement monitoring channel, not the CO2

injection channel. This is typical of that in the other tests and is provided here by way of illustration.

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Figure 4-45. . CO2 in the breathing loop against time. CO2 injection starts at 11 min. SCRB time life (2mbar PPCO2) = 71 min or 1 hour and 11 min; SCRB time life (5mbar PPCO2) = 122 min or 2 hour 2 min; SCRB time life (20mbar PPCO2) = 196 min or 3 hour 16 min;

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Figure 4-49. . CO2 in the breathing loop against time. SCRB time life (2mbar PPCO2) = 68 min or 1 hour 8 min; SCRB time life (5mbar PPCO2) = 96 min or 1 hour 36 min; SCRB time life (20mbar PPCO2) = 181 min or 3 hours 1 min;

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5 MAXIMUM INHALED CO2 LIMITS There is a problem that some standards define CO2 breakthrough at such a low level that there are no symptoms, so divers do not treat the figure seriously and go onto exceed scrubber durations without having any good data points on what the limit actually is. For example, EN14143:2003 defines a maximum inhaled CO2 limit of 0.5kPa: the U.S. Occupational Safety and Health Administration advise that average exposure for healthy adults during an eight-hour work day should not exceed 0.5kPa. As a scrubber breakthrough figure this is just not meaningful.

For exposure up to 10 minutes, the U.S. National Institute for Occupational Safety and Health (NIOSH) and American Conference of Government Industrial Hygienists (ACGIH) limit is 3kPa.

NORSOK U101:1999 takes a more pragmatic and sensible approach, giving a limit of 1kPa generally, and for short periods 2 kPa. A scrubber breakthrough event is a short period, so the limit on scrubber endurance of a 2 kPa breakthrough should be one that divers can accept.

The 2kPa limit is used by Deep Life Ltd. For certification purposes, the 0.5 kPa and 1.0 kPa

6 CORRELATION WITH THIRD PARTY TEST RESULTS Tests were carried out by Micropore at their Newark facility using a dumb head (i.e. single scrubber Open Safety Apocalypse version of the rebreather) and these correlate to within 4 minutes of the times measured by Deep Life at the 0.5 kPa calibration point used by Micropore, with 4C +/- 1.2C water and the rebreather in the vertical position, at 130 fsw.

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at DSV

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1.5 kPa 2 kPa

4.8 29.64 20.39 93.25 134.75 189.25 224.75 104.42

4.8 29.27 20.06 106.00 135.50 161.25 182.75 10.47

5.2 30.7 20.39 114.00 158.50 193.00 222.5

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7 CONCLUSION The table below tablulates the test results. Using the NORSOK U-101 2kPa limit, the scrubber life in 4C of 2 hours 45 mins seems to be a reliable figure that is lost only if the exhale temperature reduces excessively. There is no loss in performance from an interrupt of 18 hours between two dives: in fact, it is in line with other test results showing the scrubber performance improves slightly.

Table 1. Scrubber endurance test results

Temperature, C Humidity, %

CSCRB endurance, min

Water Breathing machine

Exhale Breathing loop

Scrubber Breathing machine

0.2 kPa 0.5 kPa 2kPa

Notes

4 15 32 12 25 55 77 108 165 Standard vertical test conditions. 2 hours 45

min endurance in NORSOK.

1 15 32 13 24 72 58 83 144 Standard vertical test conditions other than

water is 1C.

1 17 32 13 25 72/91 63 104 - 2nd vertical 1C test

1 16.5 32 13 25 72/93 61 96 188 3rd vertical 1C test

1 17 32 13 25 71/83 47 77 192 Vertical 1C test interrupted at 167 min

for 4 min.

5 6 10 12 18 59 91 130.5 Vertical very cold expired gas, but 18-hours-break between

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two test stages

4 12 21 10 20 42 69.3 108.7 Vertical reduced exhale temperature.

2 12 32 13 25 80/96 54 90 169 Horizontal std to cold test (first test).

3 13 32 13 26 77/95 71 122 196 2nd std horizontal test

4 14 32 13 26 65/91 68 96 181 3rd std horizontal test

The NORSOK U-101 2 kPa limit that is a practical limit for divers, is 2 hours 45 minutes. This is extended by around 20 minutes when the diver is horizontal. There is a small spread of results, so for conservatism, the manufacture will state the duration of the scrubber is 2 hours 35 minutes at 40msw, with a 40lpm RMV, using air as the diluent.

The reduction of the water temperature to 1C does not cause a statistically significant change in the duration.

A reduction in the exhale temperature does reduce the scrubber duration substantially. This underlines the importance of the biased counterlungs, and large bore diameters in the Open Revolution rebreathers to prevent gas cooling from the diver to the scrubber.

From other tests, there is no difference in scrubber duration between the instrumented eCCR head used for the Apollo Incursion and the dumb head used for the Open Safety Apocalypse rebreather product. The dual scrubber rebreather in the Open Revolution series used for the Bell Diver and Cave Diver products is the subject of a separate report.

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