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  • Guestbook2002
    good Peter K John Cockburn 21 06 02 15 02 46 Great site I was only going to have a quick look but ended up staying for well over an hour Highly recommended John Rob Davie 21 06 02 15 01 58 Jan Very simple yet elegant idea Thank you for sharing it with all Rob Davie Jens 21 06 02 12 01 49 Great and beautifully site very useful information Thanks Inspiration diver from Sweden Fil 19 06 02 12 20 11 If you love rebreathers there isn t a better site than this Thanks Fil The Garskonian 26 09 02 07 28 44 Nice web site Look me up if you are ever in the islands perhaps we can go diving Herman 23 09 02 17 11 02 Behoudens de term Rebreather en dat je daarmee je eigen lucht nogmaals gebruikt wist ik er verder weinig van Dat is nu wel over Heel informatief Z odanig dat ik voorlopig nog maar even doorga met m n gewone uitrusting al zal de intresse voor dit soort duiken wel blijven hangen Harry 23 09 02 15 45 37 want to know more about rebreathers and dive with them you site is very rich with information and detail this will prepare me a bit in advance before I start my rebreather course you can never know enough safe diving and once again great work on the site John Boudreaux 19 09 02 04 09 31 I have been looking for a new Drager Dolphin Semi Closed Circuit Rebreather to purchase If those that have the information would kindly pass that on to me that would be great Thank you in advance JBoudreaux DMS 11 09 02 10 03 37 Denkend aan Holland zie ik brede rivieren HE JW Site ziet er mooi uit Lijkt wel prof Ik zal nog eens goed bladeren maar compliment is op zijn of haar plaats Wim Breeman 25 08 02 23 41 05 Hoi Jan Willem Prima site tot nu toe de enige waar ik echt duidelijke rebreather info gevonden heb ook voor de niet rebreather duiker Roy Ettema 10 08 02 19 25 03 Nice site with a lot of wreck information Cliff Simoneau 04 08 02 15 46 36 Hello I wanted to thank you for send me notification of this site I look forward to contribution in the future Also want to let Inspiration divers know I have 2 open spots on my Inpiration Only Whale Shark and Tagging Trip in Oct of 2002 if it should interesting find out more at www c2diving com yves christiaens 01 08 02 08 21 07 Gefeliciteerd zeer informatieve en vooral nuttige info gevonden op jouw site Z odra mijn ombouw naar wens is stuur ik je de resultaten met een duikverslag Blijven volhouden Ad Vernet 31 07 02 21 20 37 Jan willem mooie site met veel goede informatie Een echte aanrader voor aspirant rebreather duikers en geintereseerden Git 29 10 02 16 24 24

    Original URL path: http://www.therebreathersite.nl/08_Website_Related_Information/guestbook2002.htm (2016-05-02)
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  • Silent List
    1975 SCR diver since 2001 Marco Polo Italian commercial diver CCRO2 2 ARO Cressi 2 SuperAROCressi NuovoARO Technisub Fenzy P 68 IDA 57 RG UF M SCR 2 Azimuth FIENO FGT 1D Oxymixgers CCCR IDA 71 IDA76 IDA 59 MCCR Azimuth KISS Gender Male info AT rebreathers it Number 020 Organization PADI NASE FIPSAS UTR TSA Level instructor Name Alessandro Fronchetti O2 SCR CCR Kiss 02 and SCR Model OMG P96 LAR 5 Azimuth Dolphin Ray RG UF M Diving rebreathers since 1994 Country ITALIA Gender male Email afronch tin it Number 021 Organization IANTD BSAC Level Full open trimix CCR trimix Name Bruce Sloan CCR Model Inspiration Hammerhead Diving rebreathers since 2001 Country Scotland Gender Male Email rebreather AT blueyonder co uk Homepage http www rebreather me uk Number 022 Organization CMAS IART Level T3 CMAS T3 Cave Diving Inspiration CCR IART Name Thomas Pinzl CCR SCR Model Inspiration Ray Dolphin Diving rebreathers since 2001 Country Switserland Gender Male Email thomas pinzl bluewin ch Number 023 Organization NAUI Level Course Director SCR Instructor Name Carsten Schulz O2 SCR CCR Kiss Ray Dolphin KISS Model KISS 63 Diving rebreathers since SCR 02 2001 CCR 07 2003 Country Germany Gender Male Email anthias at web de Number 024 Organization IANTD Level Instructor Trainer Name Ramon Maarten Model Inspiration Diving rebreathers since 2000 Country Belgium Gender Male Email m ramon AT skynet be Number 025 Organization TDI Level OC Trimix CCR MOD1 Name Simon Powell O2 SCR CCR Kiss CCR Model Inspiration Diving rebreathers since Mid 2004 Country UK Gender Male Email simon powell a bigfoot com Number 000026 Organization TDI Level OC Trimix CCR MOD1 Name Beaniel O2 SCR CCR Kiss CCR Model Inspiration Diving rebreathers since Sept 2003 Country UK Male Female Male Email rb at outlawdivers org uk nospamthankuvmuch Number 000027 Organization IANTD Level CCR MOD3 Name Zak Sherlock O2 SCR CCR Kiss CCR Model KISS Unit 40 Diving rebreathers since July 2002 Country UK Gender Male Email nope Number 000028 Organization IANTD Level Normoxic Instructor Name Rob Davie O2 SCR CCR Kiss CCR Model Expedition Inspiration Diving rebreathers since 2001 Country Tejas Male Female Male Email airlandseatrng sbcglobal net Number 000029 Organization NAUI Level CCR Diver Name Stefan Besier O2 SCR CCR Kiss CCR Model Prism Topaz Diving rebreathers since 2004 Country United States Gender Male Email stefanATscubadiving com Number 00030 Organisation IART Level MOD1 Name Ian Inglis O2 SCR CCR Kiss CCR Model Inspiration Diving rebrethers since Jan 05 Country Thailand UK Gender Male Email scotsscubagod a mac com Number 00031 Organization TDI Level CCR MOD1 Name Mdemon O2 SCR CCR Kiss CCR Model YBOD Diving rebreathers since 2004 Country UK Gender Male Email mdemon AT talk21 com Number 000032 Organization TDI PSA ITDA Level Trimix Heliox CCR IT Name Dave Cooper Model Inspiration Evolution Megalodon Diving rebreathers since 1989 Country UK France Male Female Male Email info zerogravitydiving com Number 000033 Organisation BSAC PADI TDI Level ADVANCED NITROX Name JOHN ROUTLEY O2 SCR CCR Kiss CCR

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  • Search
    This new search page offers you the possibility to search Therebreathersite nl Please sign my Guestbook

    Original URL path: http://www.therebreathersite.nl/08_Website_Related_Information/search.htm (2016-05-02)
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  • Door het oog van de naald
    meestal een druk van om en nabij de 210 bar beschikbaar bij kamertemperatuur De einddruk hangt af van de vulsnelheid en de kamertemperatuur en wordt bepaald door de wet van Boyle en Gay Lussac We merkten op dat bij toepassing van een verkeerde schroefdraadcombinatie de kraandraad in de praktijk het vaak tussen 150 bar en 180 bar begaf Om een idee te krijgen met welke kracht het gas op de kraan drukt kunnen we de volgende berekening toepassen Het contactvlak van de kraan met het gas wordt bepaald door de flankmiddellijn d2 van de draaddoorsnede van de kraan zie afb 2 Om deze te berekenen nemen we de doorsnede d 0 65p Hier is d 25mm en de spoed p 2mm De flankmiddellijn is dan 23 7 mm De oppervlakte van het contactvlak is dus 4 4 cm 2 Bij 180 bar druk zal elke cm 2 een kracht van 1800 N uitgeoefend worden De totale kracht waarmee het gas op de afsluiter zal drukken zou theoretisch daarom 4 4cm2 x 1800N ongeveer 800 kilo bedragen Een enorme kracht op deze kraan Als de kraan het begeeft vormt het een levensgevaarlijk projectiel waarna het gas explosief vrijkomt In de onderstaande tabel staan de meeste schroefdraden beschreven die de afgelopen jaren gebruikt worden voor kranen in duikcilinders Tabel Uitwendige maten van kranen Benaming kraandraad Buitenmaat in mm Spoed in mm Spoed in g inch Norm Status Vorm M25x2 25 2 nvt EN 144 1 Modern cilindrisch M18x1 5 18 1 5 nvt EN 144 1 Modern cilindrisch E 17 con 17 4 19 8 1 814 14 gpi EN 144 1 Modern conisch 25 x 2 SI 25 2 nvt Oud cilindrisch G 3 4 BSPP 26 4 1 814 14 gpi DIN 259 EN ISO 228 Oud cilindrisch NPSM ¾ x 14 gpi 26 26 1 814 14 gpi ANSI ASME B1 20 1 t6 Modern cilindrisch W28 8x 14 gpi 26 441 1 814 14 pgi DIN 477 Oud conisch Omdat tabellen zoals hierboven onvoldoende informatie bieden om de juiste draad in de cilinder te bepalen is meer informatie nodig Hoe bepalen we de juiste schroefdraad in de fles Om vast te stellen of we te maken hebben met een metrische M25x2 kraan of met een ¾ BSPP kraan kunnen we met een schuifmaat eenvoudig de uitwendige diameter meter De m25x2 kraan meet 25 mm en de BSPP ¾ kraan meet 26 4 mm Anders wordt het om de juiste draad in de cilinder vast te stellen Meten we in een cilinder met M25x2 draad is de op een schuifmaat afgelezen maat geen 25 mm Om vast te stellen met welke schroefdraad we te maken hebben maken we gebruik van een schroefdraadnorm In afbeelding 2 is een tekening van de metrische schroefdraad te zien Hier zien we dat juiste en te meten maat in de duikcilinder d 1 wordt genoemd en wordt bepaald door de buitenmiddellijn van de schroef d 25 mm te verminderen met 1 08 maal de spoed Dit is 25 1 08x2 0mm 22 84 mm Als we in de fles 22 84 mm meten kan het M25x2 zijn maar moeten we nog de spoed met zekerheid vaststellen Afb 1 De inwendige maat van een M25x2 cilinder Het meten van de spoed De spoed meten we met een schroefdraadmeter Een dergelijke meter is al te koop voor nog geen tien euro Als de draadkam 2 0 in de schroefdraad past hebben we te maken met een spoed van 2 0 mm Afb 2 Normblad isometrische draad Afb 3 Schroefdraadmeter op de kraan De passing van de kraan in de cilinder is dus een zeer nauwkeurig bepaalde verhouding tussen spoed en tophoek De conische draden van vroeger en de gasdraad R ¾ hebben een tophoek van 55 De tophoek van de M25x2 draad is 60 De spoed bij M25x2 is 2 mm Dat wil zeggen dat bij elke omwenteling de schroefdraad 2 mm in axiale richting is gestegen De spoed van de cilindrische oude ¾ draad is 1 81 mm en dit wordt op de kam weergegeven als 14GPI 14 gangen per inch De kernmiddellijn van de cilinderdraad van de cilindrische BSPP ¾ cilinder is 24 64 Tabel 2 Courante maten Maten in mm Dkraan uitwendig Dcilinder inwendig Spoed in mm Norm G3 4 26 441 24 66 1 814 Din 259 M25x2 25 22 84 2 Din 13 7 Veel van de ongelukken hebben plaatsgevonden omdat een nieuwe M25x2 kraan in een oude cilinder met 3 4 BSPP werd gedraaid De kraan zal pas na 6 8 gangen omwentelingen weerstand ontwikkelen waardoor de monteur denkt dat de kraan goed zit gemonteerd Met een grote bahco of moersleutel wordt de kraan verder vastgedraaid Zodra de kraan na de laatste twee of drie omwentelingen afdicht op de rand bestaat het idee dat de kraan goed is gemonteerd Niets is minder waar Afb 4 Levensgevaar een M25x2 kraan in een G 3 4 fles gaat er bijna helemaal in Hoe sluiten we tolerantie fouten uit Als een nieuwe kraan op een cilinder moet worden geplaatst moet van beide delen de schroefdraad bekend zijn Ook moet worden vastgesteld of de schroefdraad binnen de slijtage toleranties valt Dit geldt voor de cilinderdraad en voor de kraandraad Hiervoor zijn draadkalibers in de markt verkrijgbaar Deze relatief goedkope draadkalibers bepalen of de draad nog binnen de veilige toleranties valt Iedere onderhoudstechnicus of duikzaak zou over dergelijke gereedschappen moeten beschikken De kaliber wordt in de cilinder gedraaid met de zwarte kant en de kaliber moet dan geheel in de schroefdraad passen zie afbeelding 6 Daarna wordt de rode zijde van de kaliber ingedraaid zie afbeelding 7 Als de schroefdraad binnen de toleranties valt loopt de kaliber vast Als de kaliber ook met de rode zijde geheel in de cilinder past is de draad versleten Afb 5 Goedkeur Afkeur draadkaliber Afb 6 Kaliber past volledig in de cilinder Afb 7 Kaliber loopt vast draad is binnen tolerantie Dergelijke kalibers zijn ook beschikbaar voor de buitendraad

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  • Untitled 1
    geen afgesloten ruimte Vooropleiding Gevorderd Nitrox Duiker of Introductie tot rebreatherduiker en 60 in een logboek geregistreerde duiken Normoxic Trimix Inspiration Diver MODULE 2 Een programma om duikers op te leiden die willen duiken op dieptes tussen 27 meter en 51 meter diepte Hierbij wordt ervan uitgegaan dat niet met lucht maar met helium mengsels wordt gedoken De opleiding omvat tevens decompressie duiken Vooropleiding Adcanced Nitrox duiker Minimaal 100 gelogde duiken waarvan er 30 dieper dan 27 meter Inspiration Rebreather Diver met minimaal 20 duiken en 25 gelogde uren minimaal 18 jaar Trimix Buddy Inspiration CCR Diver MODULE 3 Dit programma is ontworpen om duikers te trainen in het veilig gebruiken van de Inspiration rebreather voor diepe duiken met decompressie uitgevoerd met helium gebaseerde mengsels Vooropleiding Buddy Inspiration Duiker Buddy Inspiration Normoxic Trimix duiker of Trimix duiker Minimaal 200 duiken en 50 gelogde uren op de Inspiration Minimaal 25 gelogde decompressieduiken op de Inspiration waarbij deco stops noodzakelijk waren Minimaal 21 jaar De opleidingen van de modules 1 2 en 3 zijn apparaat specifiek Dat wil zeggen dat een rebreather duiker in het bezit van het brevet Rebreather Duiker module 1 op de Inspiration niet bevoegd is te duiken met de Cis Lunar en vice versa Rebreathers worden door fabrikanten uitsluitend aan gebrevetteerde duikers verkocht De TDI Technical Diving International geeft twee opleidingen op het gebied van rebreathers als ik correct en volledig geà nformeerd ben Cursus SCR training Deze cursus is het beginners niveau voor recreatieve duikers die een nitrox SCR rebreather willen gebruiken De voordelen gevaren en juiste procedures zijn voorafgaand aan deze cursus al onderwezen tekst hoofdkantoor TDI Opleiding CCR voor de Inspiration met als instroom niveau Advanced Nitrox Duiker met 70 geregistreerde duiken en een minimum leeftijd van 18 jaar De opleiding bestaat uit minimaal 6 uur theorie en 2 uur onderhoudslessen en is fabrikaat gebonden Vervolgens 2 uur training in het zwembad en 6 uur duiktijd verdeeld over 6 8 duiken Het theorie examen dient met minimaal 80 score te worden behaald zie voor verdere informatie http www tdisdi com Voor zover uit de site van de RAB is op te maken beperkt de Rebreather Advisory Board RAB zich tot opleidingen voor SCR Rebreathers zie hiervoor more here NAUI TEC zie http www nauitec com Padi Semiclosed Rebreather Diver Drà ger Dolphin Atlantis Course Rebreathers worden steeds populairder voor sportduikers Hiervoor heeft PADI een speciale opleiding voor het duiken met semi closed rebreathers De opleiding is afgestemd op het gebruik van de Dolphin of Ray rebreather van Drà ger Het programma is ontworpen om je bekend te maken met deze rebreathers Om deel te nemen gelden volgende toelatingseisen a PADI Open Water Diver of gelijkwaardig certified as a PADI Enriched Air Diver of gelijkwaardig waarbij de duiker gecertificeerd dient te zijn gasmengsels te mogen gebruiken tot 40 procent zuurstof minimaal 15 jaar oud Voor overige informatie PADI Dive Center or Resort OF klik het logo hier rechts ANDI Europe biedt opleidingen op het gebied van

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  • Untitled 1
    S O 2 The O2 fraction in the injected breathing gas oxygen 100 VO 2 The volume of the diver s metabolised oxygen l min VO2 is a difficult concept The metabolic usage of a SCR diver strongly depends on the work load In general this value is approx 0 5 0 8 l min however when the diver works under water a usage up to 4 litres is possible T his variable has influence on the inhaled gas fraction Since there is a variation in the metabolic use of oxygen during the dive there will be a variation in the inhaled oxygen fraction This has a direct impact on the decompression obligation because the nitrogen fraction varies with the oxygenfraction To calculate the fraction of the oxygen content the diver is breathing we need to know a couple of things 1 The gas in the bottle 2 The metabolic oxygen consumption of the diver 3 The gas injection with this particular gas OK suppose we dive a Dolphin rebreather fitted with a 50 Nozzle intended to be used with EAN 50 the flow is fixed at 7 3 ltr min This value has to be found in the manual

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  • Untitled 1
    Supplies It is always a good idea to keep extra supplies of breathing gas aboard the surface support vessel in case of an open circuit bailout situation In most cases supplies of both oxygen and oxygen nitrogen mixtures air or EAN should be on hand and mixtures incorporating helium may be needed for more extreme dive profiles In some cases some or all of this gas will be staged underwater prior to the dive but in other cases it will remain in the surface support vessel until and if it is needed Of critical importance is that the diver can reliably reach additional gas supplies with at least a 30 margin for error should the need arrive If only one diver is conducting a decompression rebreather dive i e a solo dive the volume of total gas supply should be twice that required by the diver for a complete decompression on open circuit If two divers are conducting the dive simultaneously then the total supply should be three times the amount that any one diver would need to complete decompression in open circuit mode Teams of three or more divers might require even larger gas supplies b Surface Supplied Oxygen The emergency open circuit oxygen supply could include a surface supplied oxygen system Such a system reduces the bulk of equipment in the water which can be beneficial for extended shallow water decompression stops especially for in water recompression treatment of Decompression Sickness DCS A full discussion of these systems is beyond the scope of this article but it should be noted here that if two or more divers are conducting decompression dives simultaneously there needs to be at least one self contained oxygen supply per diver to guard against the unlikely event that two or more separated divers simultaneously need additional supplies of oxygen 3 Other Equipment Most other equipment for decompression dives using closed circuit rebreathers will depend on the particular objectives and environmental conditions of the dive Two items that most divers should carry are a sharp cutting tool and one or more sets of decompression tables The knife should be small and easily accessible by either hand and the decompression tables should include a variety of depth and bottom time contingencies as well as schedules for both closed circuit constant oxygen partial pressure and open circuit constant oxygen fraction decompression with available gas mixtures II Pre Dive In addition to general gas mixing equipment testing rig preparation team briefing and other obvious pre dive activities rebreather divers should perform several additional pre dive routines A Loop Leak Test An essential pre dive test for any rebreather is a loop leak or positive pressure test This step involves adding gas to the rebreather loop until the over pressure relief valve vents and observing for a subsequent drop in remaining loop volume or pressure that might indicate a poorly sealed connection or leak somewhere in the breathing loop B Oxygen Control System Test Another test prior to commencing the dive is a verification of the oxygen control system function Minimally this test involves flushing the loop with diluent activating the oxygen control system and verifying that the solenoid fires correctly If the unit allows the user to easily adjust the PO 2 set point the test could be conducted with a low set point such as 0 3 atm to verify that the solenoid stops firing after set point has been achieved If this latter test is conducted it is imperative that the PO 2 set point be returned to the correct value prior to the dive C Final Checklist Beyond the standard checklists frequently used by open circuit mixed gas decompression divers a separate checklist should be developed specifically for the particular rebreather unit that is to be used Minimally this checklist should include verification of absorbent type and remaining canister life accurate oxygen sensor calibration correct PO 2 set point oxygen and diluent cylinder pressures diluent gas composition s and correct position open or closed of all valves in the system Additional model specific verifications may also be required for certain rebreathers III Descent If the descent is abrupt i e a straight fast descent to depth the breathing loop should be flushed with diluent prior to commencement of the dive If the oxygen partial pressure is allowed to increase at the surface prior to the dive for example by the action of the oxygen injection solenoid there is a risk that the oxygen partial pressure in the breathing loop will exceed safe levels during a rapid descent Correction for this would involve flushing the loop with diluent at depth which results in an unnecessary loss of potential open circuit breathing gas supply If the dive is to be conducted with only helium and oxygen in the loop during the deep portion of the dive the loop should be flushed with heliox before beginning the descent Some people myself included have experienced impaired concentration when breathing heliox at depths in excess of about 250 ft 75 m following rapid descents This impairment seems to be alleviated when the nitrogen partial pressure in the breathing loop is maintained at about 2 5 3 0 atm less than the level at which significant narcosis is usually experienced There are two basic methods of introducing trimix into the breathing loop The most obvious is to use a blend of trimix as the diluent supply The advantage of this method is that the helium to nitrogen ratio remains relatively constant the disadvantage is that nitrogen partial pressure in the breathing loop increases with increasing depth hence the trimix must be blended for the maximum depth of the dive and will be ideal only at that maximum depth A less obvious method is to blend trimix from separate air and heliox diluent supplies With this method the descent begins with a loop full of air and air as the diluent supply Upon reaching a depth of about 100 ft 30 m and allowing the oxygen partial pressure to achieve set point the diluent supply is changed to heliox and the descent continues This results in a relatively constant partial pressure of nitrogen in the breathing loop calculated as ambient pressure at time of diluent change minus oxygen partial pressure at time of diluent change The advantage of this method is that the nitrogen partial pressure does not increase with increasing depth The disadvantage is that there may be deviations from the predicted nitrogen partial pressure in the event of loop volume fluctuations and loop gas venting as from mask clearings etc Combinations of these two methods are also possible but it is vitally important that whichever method is followed the software used to generate the decompression profiles both for real time decompression and backup decompression tables take into account the predicted fluctuations of the helium to nitrogen ratios IV System Monitoring Control A PO 2 The most critical variable to monitor on a closed circuit rebreather is the oxygen partial pressure in the breathing loop The PO 2 set point of the oxygen control system should be no less than 0 5 atm and no greater than 1 4 atm The lower limit maintains a margin for error above hypoxic levels and the upper limit maintains a margin for error below dangerously hyperoxic levels Although some standards allow for inspired oxygen partial pressures as great as 1 6 atm such partial pressures would be unsafe set points on a closed circuit rebreather for two reasons First oxygen partial pressures in the breathing loop can spike above set point during short rapid descents and second rebreather divers should incorporate a more conservative upper oxygen partial pressure limit than open circuit divers due to the fact that the diver is exposed to that partial pressure throughout the entire dive as opposed to open circuit dives where the PO 2 limit is experienced only at the deepest depth of each breathing mixture Each rebreather diver should become intimately familiar with the rates at which their metabolism affects the oxygen partial pressure within the breathing loop at different levels of exertion on the specific rebreather that diver intends to use For example with the oxygen control system disabled on the rebreather model that I use the oxygen partial pressure will drop from 1 4 atm to 0 2 atm over the course of about 30 40 minutes at low to moderate exertion levels My diving partner consumes oxygen at about twice the rate I do at a given workload and thus causes the same PO 2 drop to occur in about 15 20 minutes at the same exertion level Once a diver knows the oxygen consumption rates the PO 2 levels in the loop should be checked with a frequency no more than one half the amount of time it would take for the PO 2 to drop to dangerous levels For the example above if the PO 2 setpoint was 1 4 atm I would check the PO 2 in the breathing loop at least every 15 minutes and my diving partner would check his at least every 7 or 8 minutes The PO 2 should also be monitored during and after every substantial depth change Divers should also be in the habit of frequently comparing the primary PO 2 display with the secondary PO 2 display should note whether or not all oxygen sensor readings are in synchrony and should note whether the readings are dynamic or static static readings are often indicative of some sort of oxygen sensor failure Some rebreather designs allow divers to verify that sensors are providing correct readings such tests should be performed periodically throughout the dive and whenever some reason to doubt about the accuracy of the readings presents itself B Gas Supplies Although cylinder pressures are of critical importance to open circuit divers they are somewhat less critical to closed circuit rebreather divers Diluent supply pressure s should be monitored to ensure a safe open circuit bailout can be performed at any point during the dive Oxygen supply pressure s should be monitored to ensure there is a sufficient quantity of oxygen remaining in each oxygen cylinder to complete the remainder of the dive in closed circuit mode with a comfortable margin for error C Remaining Absorbent Canister Time The amount of time that a given canister of carbon dioxide absorbent will sustain a diver should be clearly and confidently known prior to the commencement of any dive For dives requiring substantial decompression there should be at least a 50 margin for error and preferably a 100 margin for error i e an absorbent canister should be able to last one and a half to two times the predicted total dive time In the absence of reliable carbon dioxide sensors the ability to reliably predict the remaining life of an absorbent canister can be difficult The most frequently used method is a simple clock of how much dive time is spent using a particular canister of absorbent Unfortunately the rate of this clock can vary among different divers and different workloads by as much as a factor of ten In the same amount of time that one diver may have completely exhausted the canister another diver may have used up only 10 of the active life of the absorbent considering the maximum possible extreme cases An alternative method of monitoring canister life is to monitor the amount of oxygen consumed This includes the total volume of oxygen entering the loop both from oxygen and from diluent supplies Calibration of this value should be done empirically under controlled conditions i e minimal venting of gas from the breathing loop with each particular canister design of each particular rebreather values cannot necessarily be extrapolated based only on volume of absorbent material A sample size of empirically derived values should be large enough such that scale of variation can be inferred Venting of loop gas during dives e g ascents mask clearings etc will result in a more conservative estimation of remaining canister life If done correctly this method of canister life prediction is probably among the most accurate assuming consistent and proper canister packing techniques and absorbent quality Divers should be on the alert for potential symptoms of hypercapnia e g shortness of breath headache dizziness nausea a feeling of warmth etc during all phases of the dive If such symptoms are suspected the dive should be immediately terminated and the ascent should commence Short term relief of symptoms following an ascent should not be interpreted as evidence that the canister is functioning properly because ascents will inherently lead to a short term drop in the carbon dioxide partial pressure in the breathing loop and often involve a concurrent reduction of workload i e CO 2 production rate Hypercapnia symptoms might also be a result of improper breathing techniques i e the skip breathing pattern that many scuba divers do which of course confers absolutely no advantage to a rebreather diver Canister failure can be tested with short duration periods of high exertion in shallow water If a diver feels unusually starved for breath after such short bursts of exertion the canister is probably near the end of its effective life note these periods of high exertion should be kept brief so as not to unnecessarily waste remaining absorbent life As discussed earlier it is probably beneficial for rebreather students to undergo first hand experience with hypercapnia symptoms as part of their basic training course D Loop Volume The volume of gas contained in a rebreather loop the hoses canister and counterlung s of the rebreather plus the diverâ s lungs is seldom fixed I define minimum loop volume as that volume of gas occupying the rebreather loop when the counterlung s are completely bottomed out and the diver has completely exhaled the gas from his or her lungs Conversely maximum loop volume is the volume of gas in the breathing loop when the counterlung s are maximally inflated and the diver has maximally inhaled gas into his or her lungs Although the magnitude of the difference between these two volumes Vmax Vmin will vary from one rebreather design to another it will always be non zero Rebreather divers must learn to maintain the loop volume close to its optimal level for their particular model of rebreather If the volume is maintained too close to Vmin the counterlungs will tend to bottom out on a diverâ s full inhalation If the loop volume is maintained too close to Vmax the overpressure relief valve will tend to vent excess gas at the peak of a diverâ s full exhalation Furthermore total loop volume will influence work of breathing due to hydrostatic effects On rebreather models with a relatively large value of Vmax Vmin the optimal volume should ideally be closer to Vmin for models with a relatively small value of Vmax Vmin the optimal loop volume should be ideally close to the mid point In either case the diver should maintain the loop volume at whatever level results in the minimum total work of breathing and gas loss E Buoyancy Scuba divers have two main components of compressible buoyancy namely the buoyancy compensator and the thermal protection suit Rebreather divers add to this a third component of compressible buoyancy the breathing loop Many rebreather divers utilize fluctuations in breathing loop volume as fine tune control of buoyancy To maintain a constant PO 2 in the breathing loop and a constant loop volume while changing depths a diver must be skilled in minor gas addition and venting techniques On descents most rebreathers will automatically compensate for a dropping loop volume by the addition of diluent Depending on the fraction of oxygen in the diluent this may also lead to a concurrent drop in loop PO 2 it should never lead to a rise in loop PO 2 because the PO 2 of the active diluent at ambient pressure should not exceed the PO 2 set point of the breathing loop This then leads to subsequent injection of oxygen into the loop by the solenoid which increases the loop volume Practiced rebreather divers should be able to indirectly detect changes in loop volume based on changes in buoyancy and work of breathing Increases to loop volume can be made by the addition of diluent or oxygen depending on whether the current PO 2 is greater than or less than respectively the PO 2 set point Decreases to loop volume can be accomplished by manually venting gas from the loop either by exhaling through the nose except for certain kinds of full face masks allowing gas to escape from the seal of the lips to the mouthpiece or dumping gas from a valve somewhere on the rebreather loop Ideally a fully dressed rebreather diver should be neutrally buoyant or very slightly negative at the surface with optimal loop volume and empty buoyancy compensator Under such conditions gas needs to be added to the buoyancy compensator only to compensate for compression of the thermal protection suit if any In any case a diver should be weighted such that he or she is close to neutral when the breathing loop volume is at or near optimal V Ascent During an ascent from a rebreather dive especially a deep dive the oxygen partial pressure in the loop will begin to drop due to the dropping ambient pressure The oxygen control system will likely begin to compensate for this by injecting oxygen however except for the slowest of ascents the solenoid valve will not likely be able to keep up the with drop in loop PO 2 due to drop in ambient pressure Although it may be tempting for a diver to help the solenoid achieve PO 2 set point by manually adding oxygen to the loop this is probably not a good idea in most cases During the ascent loop gas will be vented from the breathing loop due to expansion The diluent component of this lost gas is unrecoverable it cannot be put back in the cylinders and it is not used by the body and assuming a continuous ascent no more diluent will need to be added to the loop for the remainder of the dive The oxygen component of the vented gas however is wasted especially if the system continuously injects more into the loop to bring the PO 2 back up to set point This waste of oxygen can be minimized by allowing the PO 2 to drop relatively low during the ascent Obviously the PO 2 level in the loop should be continuously monitored to ensure that it does not drop dangerously low i e below about 0 5 atm There is seldom any real advantage to adding additional oxygen into the loop manual in a futile attempt to maintain PO 2 set point My procedure is to allow the PO 2 in the loop to drop during the ascent I manually add oxygen to the loop only if the PO 2 drops below 0 5 atm or when I reach the first decompression stop At the first decompression stop I will usually manually add oxygen to the loop to bring the PO 2 back up to set point Proper manual oxygen addition requires a great deal of practice and training itâ s easy to accidentally over compensate by adding too much oxygen escalating the loop PO 2 to dangerously high levels If oxygen is manually injected in large bursts rather than several short bursts a pocket of high PO 2 gas will move around the breathing loop for several breaths On most decompression dives involving helium during the deep phase of the dive the diver will want to flush the helium out of the loop and replace it with nitrogen I usually do this during an ascent at a depth of about 130 150 ft 40 45 m and start the flush by venting gas from the loop until the loop volume is at Vmin I then inflate the loop to Vmax with air and repeat this cycle at least three times The partial pressure of any remaining helium in the loop is negligible and will continue to drop as more gas is vented from the loop during the remainder of the ascent When I reach the 20 ft 6 m decompression stop I shut the diluent input supply and flush the loop with oxygen until the loop PO 2 reaches set point I will generally remain at this depth until the decompression ceiling has been cleared If I ascend shallower I reduce the PO 2 set point to 1 0 atm VI System Recovery and Bailout The most valuable skills a rebreather diver must learn are the skills which enable recovery and or bailout from various failure modes These skills should be practiced routinely because a diver should only rarely have to use them in a real emergency situation A Oxygen Control System Failure 1 Solenoid Failure One potential failure mode of most closed circuit rebreathers is that the solenoid valve can potentially get stuck in the open position In such a case oxygen would be continuously injected into the breathing loop and the PO 2 of the breathing loop would reach dangerously high levels relatively quickly The first response to this situation which is usually immediately evident to the diver via audible cues and an increase in loop volume is to temporarily switch to open circuit mode After the oxygen supply to the solenoid has been manually shut the diver can flush the loop with diluent until the gas is safe to breathe return to closed circuit mode and abort the dive while manually maintaining the PO 2 in the breathing loop The obvious response to a solenoid valve that is stuck shut is to abort the dive and maintain PO 2 set point manually 2 Partial Electronics Failure If either the primary or the secondary PO 2 display systems fail at any time during the dive the dive should be aborted If the automatic oxygen control system has concurrently failed the diver should manually maintain the PO 2 in the breathing loop following the functional PO 2 display 3 Total Electronics Failure A total electronics failure generally means both the primary and secondary PO 2 display systems have failed simultaneously Although an open circuit bailout will often be the most appropriate response to this situation especially if there is no required decompression stop and the dive is relatively shallow there are at least two alternative solutions a Semi Closed Operation Any closed circuit rebreather can be manually operated as a semi closed rebreather by the diver To accomplish this the diver simply vents every third fourth or fifth exhaled breath out of the loop replenishing it with more diluent The optimal rate at which exhaled breaths should be vented from the loop depends on the depth the fraction of the oxygen in the diluent and the metabolic rate workload of the diver This system is not perfect but a well trained rebreather diver should be able to maintain a life sustaining breathing mixture in the loop until reaching staged bailout cylinders or a depth where it is safe to use the Oxygen Rebreather method see below while consuming substantially less gas than a bailout in full open circuit mode would This method requires a great deal of practice while the PO 2 displays are fully functional to master Obviously appropriately conservative decompression schedules should be followed following this bailout method b Manual Gas Mixing A more difficult but more gas frugal method of maintaining a life sustaining gas mixture in the breathing loop is to manually mix oxygen and diluent within the breathing loop During the initial bailout ascent the diver occasionally adds just enough oxygen to the loop manually to prevent hypoxia from occurring the proper rate of gas injection can only be learned after much practice and experience Upon reaching the first decompression stop the diver blends the first pre calculated gas mixture Available to the diver are at least two known gas mixtures oxygen and at least one diluent with some known fraction of oxygen in it and two known breathing loop volumes Vmin and Vmax Presumably the difference between the two Vmax Vmin will not be identical to the absolute value of Vmin With these known variables the diver can create within reasonable limits of accuracy at least four different gas mixtures The first gas mixture is achieved by flushing the loop completely with diluent Once doing this the diver can manually add oxygen to compensate for the drop in volume of the breathing loop as oxygen is metabolized and carbon dioxide is absorbed by the absorbent the loop volume will drop If a diver is sufficiently sensitive to changes in loop volume the PO 2 in the loop can be maintained relatively constant The diver continues using this method until reaching a depth shallow enough where the next mixture can be blended To create the second mixture the diver flushes the loop with diluent and then achieve Vmin then manually adds oxygen until Vmax is reached After allowing the gases to mix for a few breaths the loop is vented back to optimal volume if the gas mixture is sufficiently mixed the FO 2 should remain constant The diver then maintains optimal loop volume with the addition of oxygen The third mixture involves flushing the loop first with pure oxygen followed by venting until Vmin is reached The loop is then topped off with diluent until Vmax is achieved and the loop is vented back to optimal volume after mixing has occurred This is the most difficult mixture to create because the diver must breathe in open circuit mode to avoid hyperoxia during the gas mixing process The fourth gas mixture is pure oxygen which can be maintained by using the Oxygen Rebreather method outlined below With two diluent supplies with different oxygen fractions the number of gas mixtures that can be created increases to 9 With three diluent supplies there are 16 possible gas mixtures that can be blended This method is most difficult in deep water because with a given PO 2 the FO 2 is relatively small This means that relatively small changes in loop volumes equate to relatively large changes in PO 2 This makes the task of trying to replenish metabolized oxygen considerably more difficult It cannot be over emphasized that these methods require a great deal of practice to master Practice sessions should be conducted while the rebreather electronics are fully functional so the diver can monitor the various gas flushes and how they affect actual PO 2 c Oxygen Rebreather The simplest and most reliable method of manual oxygen control is to maintain only oxygen in the breathing loop Unfortunately this method can only be used at depths of about 15 20 ft 3 5 6 m or less depending on the maximum PO 2 the diver wants to be exposed to The diver simply flushes the loop with pure oxygen and replaces and drop in loop volume with more oxygen Regardless of how precise the diver is at maintaining a constant loop volume the PO 2 in the loop stays constant at any constant depth and life sustaining at any depth shallower than about 20 ft 6 m B Partial Absorbent Canister Failure A partial failure of the absorbent canister usually means that the absorbent in the canister can no longer remove carbon dioxide from the loop as fast as the diver is producing it leading to a rise in loop PCO 2 If this occurs during a high workload portion of the dive the diver may be able to reduce workload during a dive abort and continue in closed circuit mode for a potentially substantial period of time If the partial canister failure occurs at a low workload the diver will likely need to either periodically flush the breathing loop with diluent and or oxygen in a manual semi closed mode as outlined above or resort to an open circuit bailout Once again only first hand experience will help guide the diver towards the appropriate course of action However if ample breathing gas supplies are available a they should be in all cases it is certainly more prudent to complete the dive in open circuit mode C Catastrophic Unrecoverable Loop Failure The worst case scenario for any rebreather dive is a catastrophic unrecoverable loop failure This can be caused by a severed breathing hose badly torn counterlung or completely failed e g flooded absorbent canister In such cases if a diver does not have access to a secondary rebreather system a bailout in open circuit mode is inevitable 1 Dives Without Required Decompression Stops If there is no required decompression time an open circuit bailout is the simplest solution If the diluent gas supply was monitored properly there should be plenty of breathable gas to conduct a slow controlled ascent to the surface If the rebreather system allows open circuit access to the oxygen supply a safety stop can be conducted at a depth of 10 20 ft 3 6 m to reduce the probability of DCS 2 Dives With Required Decompression Stops As stated earlier the most logistically difficult aspect of any rebreather dive requiring substantial decompression is accommodating the possible need for completing the full required decompression in open circuit mode Two general scenarios that I have developed are outlined below In both cases divers carry a total of 80 cf of diluent and as much as 27 cf of oxygen as described above in the System Configuration and Equipment section a Drift Dives Our most frequent diving method involves a live boat following free drifting divers There are many advantages to this method a discussion of which is beyond the scope of this article Herein I will describe our standard protocol for open circuit bailout from this type of dive Figure 3a illustrates the normal dive plan divers pull a tow line made from thin but strong brightly colored line that is attached to small but highly visible surface float The boat captain follows this float throughout the course of the dive keeping a watchful eye for any emergency floats that come to the surface A normal ascent from such a dive assuming no rebreather failures involves divers commencing their ascent along the tow line At a pre determined time the surface support crew clips a decompression line as described above in the System Configuration and Equipment section to the tow line via the carabineer or other similar clip at the weighted end of the decompression line Fig 3b The weight of the decompression line slides down the tow line until the divers rendezvous with it The divers then detach the decompression line from the tow line the tow line is either pulled in by the surface support crew or left to drift until all divers have surfaced and complete the decompression on the decompression line Depending on wind and swell conditions the boat may or may not be physically attached to the decompression line via a tether Fig 3c If one or both divers are forced to conduct a bailout in open circuit mode while the pair is still together both divers commence the ascent together The diver conducting the bailout inflates the emergency float that he or she has carried throughout the dive clips it to the tow line and allows it to slide along the tow line back to the surface Depending on the particular parameters of the bailout situation the diver may attach a note of explanation written on a slate that is attached to the emergency float Fig 3d As soon as the float reaches the surface the surface support crew responds by deploying the decompression line as described above In this situation however the surface support crew also attaches a pre determined configuration of open circuit breathing gas supply usually air or EAN to the weight of the decompression line Fig 3e If both divers are simultaneously conducting an open circuit bailout both emergency floats are sent to the surface and the surface support crew attaches an appropriate volume of open circuit gas supply In either case the float or floats are usually deflated and returned to the divers along with the open circuit gas supply by attaching them to the weight of the decompression line and allowing them to slide down the tow line to the divers Fig 3f When the divers rendezvous with the bottom of the decompression line they detach the tow line as described above and continue decompression A additional supply of oxygen is then sent down the decompression line by the surface support crew to a depth of 20 ft 6 m If weather conditions allow the boat to be tethered to the decompression line a surface supplied oxygen rig as described above in the System Configuration and Equipment section may be deployed instead of a self contained oxygen supply Fig 3g The ultimate worst case scenario involves a separated pair of divers who both independently and simultaneously require open circuit bailout If the first emergency float to the surface is attached to the tow line then the procedures as outlined above are followed just as if the divers were ascending together the only difference is that in this case the diver might not detach the tow line from the decompression line If a diver becomes separated from the tow line he or she will commence an ascent to the surface and will deploy an emergency float to the surface attached to the line of the reel that the diver has carried as described above in the System Configuration and Equipment section If the diver does not require open circuit bailout gas supply he or she writes a note to that effect on a slate and attaches the slate to the emergency float When the second emergency float is spotted by the surface support crew they deploy a self contained open circuit oxygen supply down the first decompression line and deploy a second decompression line to the isolated diver If there is no note on a slate to the contrary the surface support assumes the second diver is also engaged in an open circuit bailout and supplies gas accordingly Fig 3h In general the surface supplied oxygen system is not deployed whenever a diver pair is decompressing separately â it is better to allow the boat freedom to move back and forth between the decompressing divers If possible the surface support crew communicates to each diver the direction of the other diver so that the divers may swim towards each other and complete decompression together If the separated diver sends his or her emergency float to the surface first or if the two divers are both separated independently from the tow line the response procedure is similar but in the reverse order i e first come first served b Fixed Station Dives In cases where the reef extends nearly vertically from the surface to the depth of operation i e a drop off or wall the primary surface support vessel may anchor on site In this case divers run a continuous guide line from the anchor to the point at which the dive is to be conducted and set staged emergency gas supplies at various appropriate intervals along the guide line In these conditions general cave diving protocols are followed in terms of returning to the surface along the same path that the descent was made Ideally both divers will carry emergency floats and extra reels with line and a secondary chase boat will be onsite to accommodate a bailout situation as described above in case a diver becomes separated from the guide line VII System Maintenance Specific rebreather maintenance procedures will be defined by individual manufacturers for

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    works with set points Set points are values chosen by the diver A setpoint is the chosen value for the partial pressure of oxygen We would like to have a high setpoint as possible but we are limited due to oxygen toxicity We now know that in the region of 1 4 1 6 bar oxygen pressure convulsions can occur For that reason we choose a lower setpoint of 1 3 or 1 2 bar Most common a setpoint of 1 3 bar pO2 is used The rebreather will constant inject oxygen until the breathing loop contains 1 3 bar oxygen This is independent of the diving depth On the surface however the 1 3 bar will never be reached because the ambient pressure is 1 0 bar If the setpoint should be set to 1 3 bar on the surface the rebreather would continuously add oxygen For that reason there is a low and a high setpoint The low setpoint usually is set to 0 7 bar On the surface the low setpoint will cause the loop is injected with oxygen until 0 7 bar is reached When the diver enter the water he will switch to the higher setpoint below a depth of 3 meter Before the dive the rebreather needs to be calibrated There are different techniques to calibrate a CCR It is however good practice to calibrate the unit with pure oxygen If the rebreather is capable of calibrating automatically usually the mouthpiece is put in the open position and the computer injects oxygen until there is a stable reading at all 3 cells This is the reference because the measured voltage form the oxygen cells is relevant for contact with 100 99 95 oxygen High quality systems are also calculating with the ambient pressure because this is another factor to make the calibration more precise This diagram shows the fraction oxygen in the breathing air of a closed circuit rebreather versus a open circuit diver The yellow line shows a decrease in the fraction until 50 meters is reached Also visible is the switch from low setpoint to high setpoint at 5 meter Gas usage Because this rebreather has a closed cycle the only gas consumed by the diver is oxygen This consumption is only related to the metabolic use of the diver The metabolic use is related to the energy the diver uses for swimming or working Commonly a typical oxygen consumption is 1 1 5 ltr per minute That is the only gas needed by the diver when he swims at the same depth When he wants to ascent he needs to inject some gas in his dry suit or wing When he descent he have to add some gas to his counterlung to remain a breathable volume When compared to a open circuit diver closed circuit diving has a 20 times higher gas efficienty Most interesting is the fact that the CC rebreather diver uses the same amount of gas at each

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