This example illustrates the danger of overusing the absorbent. We need to measure the scrubber endurance time consistently at depth, for great lengths of time and in any water temperature. Arrows indicate the direction of gas. As mentioned earlier, for civilian rebreather diving, the European standard EN 14143 specifies how a scrubber’s endurance time must be tested. Not all manufacturers of rebreathers can either, so they have tests done at a separate test facility. The depth has an effect too. Much of the variation in the scrubber endurance times can be summarized in one term: efficiency. Cold solutions of these organic compounds bind CO2, but the binding is reversed at higher temperatures: at a moderate workload, in cold water and at the maximum depth that the rebreather will be approved for. all CO2 is absorbed. Plot of how the pCO2 in the gas leaving the scrubber changed during a test where the workload varied. I have never owned a temp stick (cant see the point) and since 2004 I have run max 6 hours on a scrubber on my Inspo, rEvo, KISS and JJ units which is based on a RMV of 15. A glass tube in which CO2 rich gas flows continuously is packed with absorbent. Tests are run at depths determined by the gas mixture used (nitrox, heliox, trimix or 100% O2). A rebreather manufacturer has to decide on the trade-off between scrubber efficiency and breathing resistance when deciding which absorbents may be used in a particular rebreather. The average expired pCO2 for a diver varies from some 2.5 to 4 kPa (25 to 40 mbar). Thank you so much for sharing the important information with all of us. The pCO2 must remain below 5 mbar (0.5 kPa). People also vary in their CO2 production so it would not be easy to get consistent numbers. If a diver works hard enough to produce lactic acid in the muscles, then the CO2 production will be well over 1 L for every L of O2. For most scrubbers it stays at zero until 60 to 80% of the absorbent is used up. Given the widely varying efficiencies of the CO2 scrubber is essentially impossible to determine what the scrubber endurance might be. They work by absorbing CO2 and releasing O2. The scrubber endurance time varies greatly due to many factors, primarily the diver’s workload and the water temperature. For nearly 10 years, CEPEDA has manufactured, tested, and serviced lithium hydroxide (Li-OH) scrubber receptacles (hoppers) for the U.S. Navy. New & Updated Supplier Purchase Order Information, Materials include various stainless steels. It appears from above that cooling increases condensation and the moisture content in the loop. If CO2 absorbent is given plenty of time under ideal conditions it will absorb a known amount of CO2. Therefore, one standardized condition is chosen. Your breathing may vary from 10 to 15 L/min to over 75 L/min. 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. These gas volumes are measured at Standard Temperature and Pressure, Dry (STPD, i.e. The red, interrupted line shows the cut-off limit for pCO2 at 0.5 kPa, 0.5%SEV (surface equivalent value), 5 mbar. Lithium hydroxide is sometimes used in cold applications. It appears in the CCR world, there is more concern on controlling temp loss (insulating hoses and canisters). However, they tend to react violently with water. When the scrubber is nearing the end of its endurance it is not capable of challenging use. However, there are many reasons why this is not a good idea. There are two reasons: 2) the rapid rise in pCO2 leaving the scrubber after it reaches this level. However, these two methods are both energy intense and are not applicable to diving. A breathing simulator is set at a minute ventilation of 40 L/min with a CO2 production of 1.6 L/min. At around 50% of the test, some CO2 started to appear, but only when the workload was moderate. soda-lime) with regards to weight and volume, and have more than 20 years of successful and safe operations of LiOH scrubber … Just like some water content of the sorb is needed for the chemical reaction to occur, too much water slows the reaction. The easiest way to judge endurance time is to graph how the pCO2 varies with time. Figure 4. The water temperature is another big factor. Levels of pCO2 above 1 kPa are best avoided. With all these factors influencing the endurance time, the 2-hour scrubber may actually last anywhere from one hour to eight or even 10 hours. Thank you for your article, very helpful. In Figure 2 some CO2 starts to get through the scrubber after about 70% of the endurance time. It may be possible to liquefy the gas by cooling it and then separate its components. Figure 3. The exact value varies with workload, how difficult it is to breathe and how much CO2 that is in the inspired gas. The hoppers have become a staple of CEPEDA's product line since we initially reverse engineered them for the U.S. Navy. Towards the end the CO2 climbs as fast as line A. When the absorbent can’t quite keep up the pCO2 may stay at an almost constant level or have a slow increase. By clicking 'OK' or any content of this site, you agree that cookies can be placed. Hence, we use a breathing simulator (sometimes called a breathing machine) to determine the scrubber endurance. Diving in 30 °C (86 °F) water may increase the endurance by another 25 to 40%. The exposure to the cold water and the decompression times involved with deep diving make tests with divers prohibitive. Several factors determine how much CO2 a scrubber will remove. Rebreather manufacturers may size the scrubber so that it should last longer than the gas supply. The efficiency is the fraction of the theoretical capacity that is actually used. They showcase the following capabilities: Home | About | Service | Quality | Contact | News | Gallery | Feedback. The CO2 load that the scrubber has to manage will change with it. Thank you very much, I will share the article as many abuse with the duration of the absorbent, not understanding the risks of this. 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. 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. Current guidance for survivors aboard a disabled submarine (DISSUB) recommends the use of the "stir-and-fan" method of carbon dioxide (CO2) scrubbing in which the contents of canisters of lithium hydroxide (LiOH) are dispersed onto horizontal surfaces. 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