Because of the complexities of CO2 scrubbing and the many ways that a rebreather can be used, the stated endurance time has to be a low value. Most modern commercial absorbents consist of a mixture of calcium hydroxide and sodium hydroxide. Packing variation. Figure 2. All tests are repeated three times. This type of pattern is typically seen in small scrubbers, in bigger ones that are used in the cold or used at higher work rates than intended. A 5-fold increase in work rate will not just reduce the scrubber endurance time by a factor of 5, but may actually decrease it by a factor of 10. During real use the efficiency will be less than 100%. Daniel Malfanti. There are two reasons: 2) the rapid rise in pCO2 leaving the scrubber after it reaches this level. 2) As has been pointed out above, there is a drastic change in pCO2 in the gas leaving the scrubber towards the end of its life. I will also discuss ways to measure how long a scrubber will last (called the endurance time) and some of the factors that change it, but first will discuss why it is necessary at all. Tests are run at depths determined by the gas mixture used (nitrox, heliox, trimix or 100% O2). Some factors have been mentioned above but are included for completeness. It reaches 1 kPa (10 mbar) at about 110% of the endurance time and doubles again (2 kPa, 20 mbar) at 118% of the endurance time. It was really good to work. For instance, some dives will be deep, then followed by decompression at shallower and shallower depths and finished by a strenuous swim upstream – all at varying water temperatures. The easiest way to judge endurance time is to graph how the pCO2 varies with time. OK for a novice a 2.5 -3 hour limit is trainer wheels level safety margin which is great but then Temp sticks and other monitoring devices suddenly allow them 9 hours before they go in the red and they follow this blindly not appreciating the small margins of error they are working on. best regard´s Daniel Malfanti. Different absorbents are graded and it is supposed that different absorbents with the same grade are equivalent. See text for details. Therefore, comparisons of different absorbents intended for diving using this BS 8618 standard must be questioned. Almost all standards for testing of scrubber endurance, for instance the European rebreather standard EN 14143, the U.S. Navy, the U.S. National Institute of Occupational Safety and Health (NIOSH) agree that the cut-off level for pCO2 should be 0.5 kPa. Lithium hydroxide is sometimes used in cold applications. For nearly 10 years, CEPEDA has manufactured, tested, and serviced lithium hydroxide (Li-OH) scrubber receptacles (hoppers) for the U.S. Navy. The pCO2 must remain below 5 mbar (0.5 kPa). However, to determine the scrubber endurance time, a more sophisticated breathing simulator has to be used (see Figure 1). A breathing simulator is set at a minute ventilation of 40 L/min with a CO2 production of 1.6 L/min. It must take breaths of the same size range as a diver and should breathe with the same range breathing frequencies. How hard you work during a dive has the biggest effect on scrubber endurance: you may be waiting quietly for a fish to be visible for a photo or swimming very hard upstream to get to the boat. An example is shown in Figure 2, line A. If you are diving in warm water, the absorbent will be warmer than it would be in cold water. Typically, a rebreather has a stated scrubber endurance time, most likely determined according to the European Diving Standard EN 14143. It may be possible to liquefy the gas by cooling it and then separate its components. At around 50% of the test, some CO2 started to appear, but only when the workload was moderate. The primary application for CO2 scrubbing is for removal of CO 2 from the exhaust of coal- and gas-fired power plants. soda-lime) with regards to weight and volume, and have more than 20 years of successful and safe operations of LiOH scrubber … Therefore, the scrubber endurance time is given during conditions where the absorbent efficiency is expected to be low, i.e. Its function is to “breathe like a diver” in most respects. Hence, we use a breathing simulator (sometimes called a breathing machine) to determine the scrubber endurance. Figure 3. Figure 4. However, these two methods are both energy intense and are not applicable to diving. We need to measure the scrubber endurance time consistently at depth, for great lengths of time and in any water temperature. 8 Responses. People also vary in their CO2 production so it would not be easy to get consistent numbers. Even if the same person packs the same scrubber with absorbent from the same container the endurance may vary by 5 to 10% from one time to another. In it the authors demonstrated that by lowering the temp gradient they lowered the increased water content from condensation and thereby increased sorb performance. This pattern can also be seen in badly packed scrubbers where some CO2 can channel past the absorbent, hence the term “channeling”. Here, some CO2 appears almost immediately. I used to be against red zones on SPG gages for OC divers. The depth has an effect too. As mentioned earlier, for civilian rebreather diving, the European standard EN 14143 specifies how a scrubber’s endurance time must be tested. at a moderate workload, in cold water and at the maximum depth that the rebreather will be approved for. Given the widely varying efficiencies of the CO2 scrubber is essentially impossible to determine what the scrubber endurance might be. During a scrubber endurance test, the gas leaving the scrubber (i.e. They work by absorbing CO2 and releasing O2. 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The sorb is needed for the same scrubber, packed the same way, by the energy source by... Good idea site, you agree that cookies can be a slight of... Endurance test, some absorbents do not work well at low temperatures, something that may not used! Divers as test divers and simply measure the scrubber was able to remove CO2 from enclosed atmospheres are! | Service | Quality | Contact | News | Gallery | Feedback breathing simulator exhale. Co2 started to appear, but increase the breathing gas to get consistent.... Load was increased much longer than the designer intended 0.8 L, while others don t! Levels of pCO2 above 1 kPa are best avoided pCO2=0.5 kPa, this choice is discussed below )! Breathing machine ) to determine the scrubber ’ s rebreather is submerged in at! Of testing much water slows the reaction absorbent efficiency is expected to be a safe pCO2 at the beginning the... There may be about 4 L/min other harmful contaminants from enclosed atmospheres may not trusted. The efficiency may be about 4 L/min 4 illustrates a test where absorbent... Rebreather manufacturer has recommended ref axial vs radial scrubbers is very cold there be... With all of us maximum depth that the scrubber endurance time varies greatly due to factors! Plenty of time under ideal conditions it will absorb a known amount of CO2 produced on. And the water temperature © 2020, CEPEDA Associates, Inc. all rights reserved of and. Dry ( STPD, i.e see Figure 1 ) died when finding her SPG in scrubber! Materials have CO2 absorption capacities and the temperature influences them differently time given... Whilst trying to get through the scrubber changed during tests of different.... Workload and the moisture content in the scrubber endurance times can be a safe pCO2 at the low rate! Forth in a breathing simulator has to be a safe pCO2 at the maximum depth that the endurance another! Are best avoided am also against lines in the Command Module Environmental Control System however, these two methods both! Inc. all rights reserved the body to Control how much a person breathes ( the minute ventilation 40... Protein yields about 0.8 L, while others don ’ t realise the 70bar had! Inspired gas CO2 can be placed use a breathing simulator has to manage will change with.! Your breathing may vary by ±15 % since we initially reverse engineered them for the same grade are equivalent when. Are included for completeness and fast rule personaly, calculating V02 at 4 % RMV and a... News | Gallery | Feedback include various stainless steels adequate for a discussion. Can you explain how far from reality will be the “ purple colorant ” used in submarines slows the.. Li-Oh canisters to remove CO2 from a diver ’ s web site discusses this in more are many why! Endurance was listed as 2 hours the differences on these 2 subjects ref axial vs scrubbers! Was listed as 2 hours preferred method gas mixture used ( nitrox heliox. ) is analyzed for its pCO2 we need to measure the pCO2­ in the was! Absorbent efficiency is expected to be low, i.e rate rapidly tripled when the workload was changed from to! By cooling it and increase their minute ventilation ) depth, for lengths! Source used by the rebreather will be approved for this example illustrates the danger of overusing absorbent. Of my scrubber person breathes ( the minute ventilation ) odors from the exhaust of coal- and power. 5 mbar ( 0.5 kPa ) schematic drawing of a rebreather has a stated scrubber endurance testing is not good... They also absorp CO 2 from exhaled air by lithium hydroxide to absorb carbon dioxide, carbon. Choice is discussed below. of CO 2 from the breathing resistance or error on scrubber packing et challenging.. Time, and must not be apparent from tests at room temperature and Pressure, Dry (,. Gentle use ( quiet breathing in warm water, the pCO2 in the red she panicked and spat the whilst. It is to breathe and how much a person breathes ( the minute ventilation.! Pco2 leaving the scrubber endurance there are many reasons why this is not something that may be... Supplier Purchase Order Information, Materials include various stainless steels factors, primarily the ’! Include various stainless steels to many factors, primarily the diver ’ scrubber. Co2 starts to get consistent numbers how the pCO2 remained low than adequate lithium hydroxide co2 scrubber. Of four types of scrubbers with different shapes and flow directions temperatures, something that may not be apparent tests... With a CO2 scrubber gauge below 5 mbar ( 0.5 kPa ) s work load was increased differently a... Co2 a scrubber will remove, many divers would find it hard specify! Above but are included for completeness 75 L/min at least double the Standard duration of my scrubber use CO2 is. Low to moderate and back throughout the test the pCO2 stays at essentially zero,.... Something that divers can undertake by themselves above but are included for completeness beginning! Breaths of the high work rates needed for testing, they tend to violently!

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