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The Model Based Dive Computers. with Its Capability for Multi-Level And

The Model Based Dive Computers. with Its Capability for Multi-Level And

ORCA INDUSTRIES' DIVE COMPUTERS

Paul A. Heinmiller ORCA Industries, Inc. 10Airport Way Toughkenamon, PENNSYLVANIA 19374 U.S.A.

TheORCA Industries EDGE Dive Computerwas the first modelbased di ve computeravailable to recreationaldivers. After six years in thefield, andthe releaseof the SkinnyDipperas the secondin the series,over ld million divesare estimatedto havebeen made using the ORCA model.Bends incidence to datehas been minimal, and less than comparable rates usingthe U.S,1Vavy tables. ORCA continues to improvehard~are andsoftw are, and plans to releasethe third computer of theseriesin 1989,

ORCAIndustries was formed in 1982to develop.a revolutionary element of diving technology,the EDGE . The EDGE was unique because it was the first of themodel based dive computers. With its capability for multi-level and repetitive diving, theEDGE extended dive times and increased pmxiuctivity for workingdivers. Its graphic tissue-trackingdisplay has helpededucate many divers about the mathematicsof decompression.Since it implementsa ceiling depth, instead of fixedstops, for dives requiringdecompression, it allows diving flexibility which was previously unavailable. TheEDGE is a largeunit, with a fullrange of decompressionfunctions, many of whichare unnecessary for theaverage recreational diver. In 1987,ORCA added the SkinnyDipperasthe second computer in the series. Using the time-tested ORCA model, SkinnyDipperwas designed with the recreational diver in mind.It presentsan instinctive displayof information,consisting of remaining no-decompression time,depth, and dive time,and doesn't have the EDGE graphics. SkinnyDipper is smaller, lighter, and less expensivethan EDGE, and has proven to bevery popular. Although it doesn'thave the EDGE'scapability for decompression information display, it does display a ceilingdepth anddoesn't lock up or shutdown in decompressionmode. ORCAremains the leader in DiveComputers, andwill presentthe third computer in theseries at DEMA 1989. The new computer, asyet unnamed, will implementstrong pointsof bothEDGE and SkinnyDipper, andshould prove to be a verycapable machine.

WARRANTY DATABASE ORCAmaintains a computerdatabase of EDGEand SkinnyDipper warranty information.Included in thedatabase are the owner's name and address, of course,but alsoinformation about the owner's diving style and frequency. Analysis of thedatabase showsthat EDGE and SkinnyDipper owners are relatively similar people, which was not expectedgiven the different marketing targets.

35 Langand Hamilton Eds.!: AAUS DC WORKSHOP. U.S.C. Sea Grant Pmgram, Los Angeles, CA, 1989

EDGE ownersreturn warrantycards for 65% of all units sold.They are,in general, olderdivers who can afford the more expensive computer, with 56%over 35 yearsof age, andonly 7% younger than 25. They report an outstanding number of divesper year, the databaseaverage is 82for thosewho responded. The different age groups report different averages,with the under 25 group at 101dives/year, the 25-35 group at 91 dives/year, and theover 35 group at 75 dives/year,This is understandable,since many EDGE owners take multiple,intensive dive trips each year, and justify the expense of theinstrument by the increaseddiving that it provides. SkinnyDipperowners only return warranty cards representing less than 30% of all unitssold. They have a similarage distribution to EDGEowners, with 7% under 25, 33% 25-35,and 60% over 35. They report a smallernumber of divesper year, with a database averageof 62.The averages for thedifferent age groups is alsoless than the corresponding EDGEgroup, with the under 25 group making 65 dives/year, the 25-35 group making 75, and the over 35 group making 54. This informationon the agedistribution and diving frequency of ORCAcomputer ownersallows us to estimatethe number of divesrepresented by thewarranty database. It is assumedthat each computer only makeshalf thenormal dives during the year that it is purchased,except for SkinnyDippersin 1987, which are only given 25% of annualdives due to late release.The individuals in the databasenot reporting ageand dive information axeassumed to have a similar distribution to thosewho did report. Finally, the average numberof divesper year for eachage group is assumedto be 50 dives/yearfor each EDGE,and 38 dives/yearfor eachSkinnyDipper in the field for the full year.All assumptionsarechosen to beconservative, soas to underestimatethenumber of dives performed. Includingonly warranty data, and not dives by theentire owner population, at the end of 1987there had been207,000 dives on EDGE, and 12,900dives on SkinnyDipper. At theend of 1988,only within the warranty database, EDGE will havelogged 430,000, andSkinnyDipper 112,600. This data is presentedin spreadsheet form in theappendix. The analysisof cumulativedives can be extendedto the entireORCA computer ownerpopulation. Those owners not represented in the warranty database are assumed to besimilarly distributed to thosewho returned warranty cards, In makingthis estimation, productionrecords are used to represent the number of newcomputers in the field each year.Computers using the ORCA model made by other manufacturers arenot included in this analysis.Other assumptions are identical to thosemade in thewarranty database calculations. Figure1 showsthe estimated cumulative dives for all ORCAcomputers from 1983 to the end of 1988.Contributions from the threedifferent age groupsand both computers areshown. The steady growth of EDGEdives can be seen, with cumulative totals of only 30,000in 1984,115,000 in 1985,274,350 in 1986,and 584,725 by theend of 1987.By the end of 1988,EDGE dives will havereached over one million. The influenceof SkinnyDipperis seenbeginning in 1987,with 50,000additional dives on theORCA model,for a cumulativetotal of over635,000. With 466,000SkinnyDipper dives by the end of 1988,there will havebeen over 1.5million divesmade on the ORCA model. AlthoughFigure 1 alsoshows the breakdown of divesby agegroup, in additionto computertype, it is difficultto seethe exact distribution of agegroup. Figure 2 displays thisdata directly, showing that, for theyear-end 1988 data, 57% of thedives are made by the over-35group, 36% by the 25-35 group,and only 6% by the under-25group.

36 Heimniller.Orca Industries'Dive Computers

While it is not possible to place an exact number on the size of the ORCA decompressionmodel diving exposure, these extremely conservative estimates can give us a generalidea of the scale involved.

Figure i. Cumulativedives on ORCA computers 1984 I 988 1.60 1.50 1.40 1.30

V! 1.20 Z 0 1,10 1.00 0.90 o.eo 0. 70 o. 60 0.50 0. 40 0.30 O.20 0.10 0.00 1984 1986 1987 I 988

DIVliNGYEAR

BENDS INCIDENCE At the1988 Annual Scientific Meeting of theUndersea and Hyperbaric Medical Society,Joel Dovenbarger presented a paper prepared by Vann, Dovenbarger, Wachholz, andBennett, discussing dive computer bends cases. There were 38 cases, effective year- end 1987,experienced by usersof divecomputers. Cases of obvioususer error were discarded,aswere inappropriate reports such as that of theperson diving with a buddy whowore an EDGE. All 38cases were not attributable to persons wearing EDGE or SkinnyDipper,as other computers are available. For thepurposes of discussion,let us assumethat all caseswere marks against the ORCA decompression model, or theuse of modelbased dive computersin general. In hisFebruary 1988 Column in SkinDiver Magazine, Dr. Fred Bovecites bends incidence figures for the useof the U.S.Navy Standard Air DecompressionTables. The source of his figuresand the assumptions involved is not mentioned.It is notunreasonable to assume that the figures represent the gross bends incidenceattributable to theNavy tables within the Navy diving population. Furthermore, weshould note that these figures are based on people diving the tables in thereal world, withwhatever errors and fudge factors this involves. His figures are 9 casesper 100,000 divesfor diveswithin the no-decompression limits, and 38 casesper 100,000dives for decompressiondives. The U.S. Navy makes predominantly single no-decompression dives,with singledecompression dives less common, The Navy tends not to make Langand Hamilton Kds.!: AAUS DC W'ORKSHOP.U.S.C. Sea Grant Program, Los AngeLes, CA, 1989 repetitive,multi-level, no-decompression dives over a numberof consecutivediving days, which is extremelycomttion to recreationaldiving vacations.

Figure 2. Distribution of cumulative ORCA dives

BY AGE GROUP,YEAR END 1988 UNDER25 .4'!

25-W 6.l X!

OVER35 7.2K!

Using the cumulativedives on the ORCA modeland the numberof reportedbends casesat year-end 1987, the gross bendsincidence of the ORCA model is 6 casesper 100,000 dives. Since this is for all dives, not just no-decompression,it does not corresponddirectly with either of the U.S. Navy statistics.It comparesfavorably with the 9 cases/100,000Navy no-decompressionfigure, and is one-sixth of the decompression dive figure. This is in spiteof the typical computervacation dive history of 3-5 multi-level dives per day, for five to fourteen day trips. These numbers can only provide a conservativerough estimate, given the errors of reporting and the uncertainty of the denominator,but they leadus to acceptthe ORCA decompressionmodel for the depthsand exposurestypical for recreationaldivers.

ORCA PHILOSOPHY

ORCA is constantlyalert for ways to fine-tunethe hardwareor the decompression modelto the benefitof recreationaldivers. The EDGE/SkinnyDipperalgorithm is not valid at altitudesabove 2000 feet, as it becomesless and lessconservative at increasingaltitude. An altitudealgorithm hasbeen developed for usein future computerswhich will eliminate the problemsof using ORCA computersabove sea level. This algorithm will producethe time-testedORCA modelat sealevel, andadjust conservatively for altitudeexposures.

38 HeinmiHer.Orea Imkstrt'es'Dive Computers

We listen to our computerowners, and othersinterested in future dive computers, and try to implementtheir suggestionsfor the improvementof the next generationof dive computers.Such featuresas better graphics,display lighting, logging, and more are beingconsidered for new products.

ORCA is also seriously interested in education and training of the diving population,as we feel that the bestand safestcomputer owner is a well educateddiver and consumer.We supportinstructor training programsand the developmentof dive computer specialtycourses in thescientific community, all recreationalagencies, and the military. We plan on continuingas the major in dive computersinto the next decade,as well asthe next miilenium.

LITERATURE CITED Barshinger,C. and K.E. Huggins. 1983.The EDGE, OwnersInstructional Manual. Orca Industries,Toughkenamon PA 19374U.S.A.

Bove, F. 1988.Medical Column - Skin Diver Magazine,February 1988 issue. Budinger, W.D. and J. Fulton. 1986. SKINNYDIPPER. Owner's instruction manual. Orca Industries,Toughkenarnon PA 19374U.S.A.

Vann, R.D., J. Dovenbarger, C. Wachholz and P.B. Bennett. 1988. DCS and decompressionmeters. Undersea Biomedical Research, Supplement to Vol. 15. Abstract page 64. Annual Scientific Meeting of the UnderseaHyperbaric and Medical Society,Bethesda, MD 20814

APPENDICES

A. ORCA EDGE Warranty DatabaseSummary Statistics

WARRANTY CARDS ON FILE

~A~r~u Age

1984 NA NA NA 166 166 1985 NA NA NA 225 225 1986 28 233 438 511 1210 1987 149 877 1238 97 2361 1988 76 370 533 27 1006 YearMissing 0 1 1 1584 1586

Total 253 1481 2210 2610 6554

39 Lang and Hamilton Eds.!: AAUS DC WORKSHOP.U.S.C. SeaGrant Program,Los Angeles,CA, 1989

PERCENTAGE OF WARRANTY CARDS ON FILE

1984 NA NA NA 2.53 2.53% 1985 NA NA NA 3.43 3.43% 1986 0.43 3 56 6 68 780 18.46% 1987 2.27 13.38 18.89 1.48 36.02% 1988 1.16 5.65 8.13 0.41 15.35% YearMissing 0.00 0.02 0.02 24.17 24.20%

Total 3.86 22.6 33.72 39.82 Percent Response 6.41 37.55 56.03

AVERAGE NUMBER OF DIVES PER YEAR FOR THOSE REPORTING

A~~gg Age

1984 NA NA NA NA NA 1985 NA NA NA NA NA 1986 133 105 82 102 91 1987 112 92 74 72 83 1988 69 80 70 69 74

Total 101 91 75 82

DIVES REPRESENTED BY THE WARRANTY DATABASE

9W 1985 986 98 1988

1984 50 166 4150 83GO 8300 8300 8300 1985 50 225 5625 11250 11250 11250 1986 5G 1210 30250 60500 60500 1987 50 2361 59025 118050 1988 50 1006 28150

4150 18075 67875 206950 430200 4150 13925 49800 139075 223250

B. ORCA SkinnyDipper Warranty Database Summary Statistics

WARRANTY CARDS ON FILE

A~~rqy~ Age

1987 77 442 817 21 1357 1988 168 839 1477 51 2535 YearMissing 0 3 4 282 289

Total 245 1284 2298 354 4181

40 Heimniller: Orca industries'Dive Computers

PERCENTAGE OF WARRANTY CARDS ON FILE

he Gmm Age T 1987 1.84 10.57 19.54 0.50 32.46% 1988 4.02 20.07 35.33 1.22 60.63% Year Missing 0 0.07 0.10 6.74 6.91%

Total 5.86 30.71 54.96 8.47 100.00% PercentResponse 6.40 33.55 60.05%

AVERAGE NUMBER OF DIVES PER YEAR FOR THOSE REPORTING

Age Mi in 1987 84 78 57 82 65 1988 56 74 52 181

Total 65 75 54 62

DIVES REPRESENTED BY THE WARRANTY DATABASE

AverageNumber of 1987 1988

1987 38 1357 12892 51566 1988 38 2535 48165

CUMUIA.TIVE 12892 112623 ANNUAL 12892 99731

41

THE DATAMASTER II A FUNDAMENTALLY DIFFERENT DIVE COMPUTER

John E. Lewis 4524 Palos Verdes Drive E. Rancho Palos Verdes, CALIFORNIA 90274 U.S.A.

INTRODUCTION

At the presenttime, there are ten or more dive computersbeing sold within the United States.They comein a widevariety of sizesand shapes,and eachdisplays data that is relevant to a diver. They all incorporate state-of-the-art electronics that produce exceptionallyaccurate and reliable measurementsof depthand time. Only one usesa table calculation, and all of the rest rely on a matheinaticalmodel or algorithm to predict the decompressionstatus of a diver.In my judgment,the most importantcontribution that the dive computerhas made to recreationaldiving is the introductionof accuratelymonitored multi-level diving, a conceptdescribed by Graver979!, and morerecently verified by the experimentsof Huggins 983! and Powell 987!. Since the table calculation design representsno advantagebeyond a table,I will not discussit further. Instead,I shall focus on the algorithms, wherein lies the fundamentaland profound difference between the DatamasterII and all of the remaining dive computers.

DECOMPRESSION THEORY

The decompressiontheory originally conceivedby Haldane and his co-workers Boycott et al, 1908! and used by Workman 965! to produce the U.S. Navy Diving Tables predicts the nitrogen loading of six hypothetical tissuesor compartments.Each compartmentis assigneda "half-time"and a maximumallowable surfacing value known as an "M-value". The U.S, Navy no-decompressionlimits and all ten foot decompression stopsare derived by calculationsbased on thesetwelve numbers.

At a constantdepth, the to the governingequations can be expressedas an exponentialfunction of time, and the model previouslydescribed is commonly referredto as an "E-E Model". This model predictsthat the uptakeand elimination of nitrogen takes place at the samerate. The algorithm usedby the EDGE is an E-E Model, and the term EDGE-like refers to this model and all dive computers that use it.

The U.S. Navy Repetitive Dive Tables representa major departure from this theoreticalmodel. Residual nitrogen times are based on the slowest20 min! compartment desGranges, 1956!. The algorithmdesigned for the DatamasterII accuratelyreplicates the residualnitrogen time of the U.S. Navy RepetitiveDive Tables.It achievesthis not by a tablelook up, but by allowing the 120min compartmentto controlrepetitive diving.

Qn a singledive, multi-level or not, the performanceof the DatamasterII and the EDGE will be difficult to distinguish. The reason for this is that multi-level diving is governedby depthdependent compartment control and not by nitrogenelimination. Since the EDGE and the Datamaster II have similar no-decompressionlimits, they produce very similar multi-level profiles.

43 Lang and Hamilton Eds.!: AAUS DC WORKSHOP.U.S.C. SeaGrant Program,Los Angeles,CA, 1989

Repetitivediving is an altogetherdifferent issue. The EDGE will allow significantly more bottom time than the DatamasterII for repetitive dives, with the difference most pronouncedfor deepdives and shortsurface intervals. Ordinarily, what works is what counts.However, when it comesto what does not work is the more important issue, and in the next section I shall review the data base.

DATA BASK

"Rememberwhen discoursing about water to induce first experience, then reason"...Leonardo da Vinci

Any applied mathematicianconfronted with Haldane'stheory, Workman's M- values, and des Granges' need to construct a single table for all repetitive diving contingenciesis logically leadto theconclusion that a micro-processorprogranmed with an E-E Model is the proper design solution for a dive computer.Thalmann 984, 1986!, while lead to this obvious conclusion, was nevertheless prudent enough to test it. The following arequotes from Thalmann'sreports: 'The mostsignificant finding of this studywas thefailure of the E-E Model to adequately compute safe repetitive dive profiles without seriously reducingno-decompression limits"...Thalmann 984!

"While it appears that some increases in repetitive no-decompressiontimes are likely, the E-L Modelpredicts sometimes that are too long"...Thalmann 986! The E-L Model that Thalmannrefers to in the secondquote has a linearelimination that is more conservative than an E-E Model, but is less conservative than the U.S. Navy RepetitiveDive Tables.

One can only concludethat repetitive diving at the U.S. Navy no-decompression limits cannotbe reliably predictedusing an E-E Model. However, it is important to note that both the EDGE and the DatamasterII have reducedno-decompression limits. The ultrasonicDoppler experimentsof Spencer976! demonstratea substantialreduction of bubbleformation for reducedno-decompression limits, and it is certainlyplausible that this can be expectedto lead to a reducedrisk of decompressionsickness. The question is whether this alone is sufficient or whether a slower elimination algorithm is also necessary for repetitivedive control.

Figure 1. is an attemptto qualitativelyillustrate the designenvelope, those regions that have been validated, and those that have been demonstrated to fail. The vertical axis representsM-values that are directly related to the no-decompressionlimits for a single dive. The horizontalaxis representselimination half-times, which controlrepetitive diving. The E-E Model allows the 5 min. compartmentto relax with a 5 min. time scale,whereas the U.S. Navy effectively usesa 120 min. time scalefor all compartmentswhen dealing with repetitivedives. The U.S. Navy Dive Tables fall in the upper right hand corner of Figure 1., and they represent the most extensive data base that we have, namely thirty years of demonstrated reliability. If one adds to this experience the data of Spencer, one arrives at Lewis: The Datamaster l1

thedesign ofthe Datarnaster II that lies in thelower right hand corner. Inthe upper left handcorner is a regiondemonstrated byThalmann toproduce unacceptable DCS. In the lowerleft hand corner are the EDGE-like dive computers, and this is largelyuncharted territory.Largely, but not entirely. Edmonds 988! tested the EDGE against several deep 20 to 147ft! repetitivedives that the Royal Navy had shown produced DCS after the thirdexposure. The EDGE not only allowed the third dive, but several thereafter. Figure 1. Dive computerdesign envelope

M-VALUES

5 MIN E-E MODEL! 60 MIN 120 MIN

ELIMINATION RATE All EDGE-likedive computers will allowrepetitive dives to depthsin excessof 120 ft, withsurface intervals ofless than 60 min., and with bottom times of the repetitive dives virtuallyidentical tothat of thefirst dive. These profiles are undeniably unsafe and should beavoided. Edmonds' admonition torestrict repetitive dives to 30ft isprobably overly conservative,butin theabsence of further testing, it is notpossible to quantifywhat is a safedepth for repetitivedives using these dive computers. Whilethe EDGE-like dive computers areunsafe for some set of repetitivedives, the DatamasterII is inoreconservative than is necessaryfor perhapsan even larger set of dives.When the Datamaster II was first designed, theU.S. Navy Dive Tables represented theonly significant data base for repetitive diving. That is nolonger true. In 1987,Powell presentedthe results of a seriesof experiments that were designed toproduce a newset of divetables for recreationaldivers Powell, 1987!. The prenuse was that recreational divers neverreach the limits of compartmentsslower than 60 min, and therefore repetitive dive timescould be substantially increased. Whether this hypothesis stands the test of 6 dives per day for 6 daysin a rowremains to be seen.Regardless, this importantdata set

45 Langand Hamilton Eds.!:AAUS DC PORKSHOP.U.S.C. Sea Grant Program, Los Angeles,CA, 1989 demonstratesthat there is a substantialregion of intermediatedepths and times for which theU.S. Navy Repetitive Dive Tables, and thus the Datamaster II, areoverly conservative. Unfortunately,these data do not include repetitivedeep dives nor repetitive shallow dives with long exposures.The former is a directtest of fastcompartment elimination, and the latteris a testof slowercompartment buildup. A dive computershould allow what hasbeen shown to be safe,but must not allow what hasbeen shown to be unsafe,Further, it shouldnot allow dive profiles that areradical departuresfrom thosethat havebeen tested. An algorithmis not magic.It is simply a meansby which one can extrapohtelimited experienceto new circumstances,and it is only asreliable as the database upon which it hasbeen tested.

SUMMARY

The DatamasterII Dive Computer utilizes a decompressionalgorithm that is profoundly different thanother presentlyavailable dive computers.The performanceof the DatamasterII andany EDGE-likedive computerwill be remarkablysimilar for a singleno- decompression multi-level dive. For repetitive diving, the Datamaster II will be considerablymore conservative.Arguably, the DatamasterII is too conservativefor some intermediatedepth repetitive dives. Demonstrably, the Edge-likedive computersare unsafe for deeprepetitive dives, and at presentit is not possibleto define a safedepth for their use whenrepetitively diving deeperthan 30 ft.

LITKRATURK CITED

Boycott, A.E., G.C.C. Damant and J.S. Haldane. 1908. "The prevention of compressed- air sickness", J. Hyg., London.

des Granges, M. 1956. "Standard air decompressiontable", U.S. Navy Experimental Diving Unit Report 5-57, Wash., D.C.

Edmonds,C. 1989, Dive Computers The Australian Experience.In: Lang, M.A. and R.W. Hamilton Eds.! Proceedingsof the AAUS Dive Computer Workshop, U.S.C. CatalinaMarine ScienceCenter, Sept.26 - 28, 1988.American Academy of Underwater Sciences,947 Newhall Street, Costa Mesa, CA 92627.

Graver,D. 1979."Using the U.S. Navy Dive Tablesfor ", Decompressionin Depth,PADI publication,Santa Ana, CA.

Huggins, K.E. 1983. "Ultrasonic Doppler study of multi-level diving profiles", ORCA Ind. publication,Toughkenarnon, PA Powell, M.R. 1987."Recreational ...thenext generation",PADI publication, Santa Ana, CA.

Spencer, M.P. 1976. "Decompression limits for compressed air determined by ultrasonicallydetected blood bubbles".J. Appl. Physio.40.

Thalinann,E.D. 1984. "PhaseII testing of decompressionalgorithms for use in the U.S. Navy underwaterdecompression computer", U.S. Navy ExperimentalDiving Unit Report 1-84

46 Lewis: The DatamasterIl Thalmann,E.D.1986. "Air N>02 decompression computeralgorithm development", U.S. NavyExperimental Diving Unit Report 8-85 Workman,R.D.1984. "Calculation ofdecompression schedulesfor nitrogen- and helium-oxygendives",U.S. Navy Experimental DivingUnit Report 1-84.

47

THE SUUNTOSME-ML PRESENTS THECONCEPT OF MULTI-LEVELDIVING RonColey, Bill Oliverand Ari Nikkola SeaQuest/ 2151Las PalmasDrive Carlsbad,CALIFORNIA 92009 U.S.A.

distanceItbreak isa upwarm the clearhorizon. day, Thethe watersky isis cobalt glassy bluecalm. andIt onlyis a scatteredperfect daycloudsfor diving offin the WesternCaribbean. Thekind of day that you would travel halfway around theworld for. Infact, most ofthe divers onboard thesmall had done just that. Thiswas their one week. The week they saved andplanned anddreamed aboutfor thelast year. Dreams aboutthis one week were often theonly thing that made lifein the hustleCaribbeanandscene, bustle theofdivemaster the "day tohad day a problem.grind" bearable. Despite theperfectness ofthe knowledge,Thereandweretemperament. a dozen diversAlmoston halfboard. had Varying some typedegreesof dive ofcomputer.skill, physical condition, "OK,here is theplan" the started. "The top of thereef is at approximately40feet here, themaximum depthfor this dive will be 100 feet. I don't want anyonetodescend below me! Those ofyou diving with tables, beback on the boat in20 minutes.Theones diving with computers mustbeback inan hour, nomatter howmuch air youhave left!" He raised his voice to make his point. Thefaces ofthe "table divers" grew long. Why were they being penalized? the ofdivemaster timeseach hadday. seen this reaction before.It is a scenethatplays itself outliterally hundreds divesandThehow diving we industryteach decompressioniscurrently examiningtheory. Now,thewaymore wethan dive, everhow before, we trackall divingthose professionalsneedtohave a greater understanding ofbasic .Likeit ornot, we are in the midst ofa greattechnological revolutionin . Thereisa desperateneedtoprovide more information tothose interested in applyingthisnew technology totheir diving activities. ItwiH be up to the diving instructors todetermine howthe industry makes thetransition tomulti-level diving. Itis now, and alwayshasbeen, theinstructor's jobto educate divers about theproper useof new technology,advancesin equipment, andchanges indiving practices. Divecomputers are willnodifferent. come along Andandwe affectcan allour rest sport. assured thatthis is not the last technological advancethat leveldiving,You willnot computernotice thatcontrolled. we started Thethisdiverarticle willby alwayscalling beitin "computer-assisted" charge andany claimsmulti- to thecontrary aremisleading andwrong. BothSea Quest, Inc.and Suunto ofFinland firmly believethatthere isa "NEEDTOTEACH" theprinciples thatgointo the design andproper

49 Langand Hamilton Eds.!: AAUS DC WORKSHOP.U.S.C. Sea Grant Program, Los Angeles, CA, l989

useof divecomputers. Not just ours,but all suchdevices. No onehas come up with a way to rep1acecommon sense, diving skills and the basic concepts of decompressiontheory. Instructionon theproper use of multi-leveldiving techniques goes far beyondthe typical owner's manual of our computer,or any device, including tables of all configurations.This beliefled us to developa supportprogram designed to assistdiving instructors.The "NEEDTO TEACH"program includes: Instructor guides, student work books,dive planningslates, multi-level log books,and two different instructionalvideos. We soughtout noteddiving authoritiessuch as Dr. GeorgeLewbel, Dr. Bruce Bassett,Dr. SylviaParle, Dr. TomKeuman, Dr. TomRhodes, and many other specialists, to help us presentthis informationin a waythat could be usedby any qualified instructor, regardlessof certifying agency.

Our instructional program is designedto allow instructorsto structureand teach accordingto their chosendiving philosophiesand their student'sneeds. The instructorscan adaptthe program'saides to their diving communities'regional differences and to the practicesof their certifying agency.

WHY THE SME-ML IS THE WAY IT IS TheSuunto SME-ML is a truemulti-level dive computer. It takesinto accountall thevarious depth segments of a diveand the precise amount of time spentat eachdepth, mathematicallymodeling theoretical nitrogen in-gassing and out-gassing according to appropriatepressure differentials. We modified the Haldaneanmodel, which has beenthe basisfor almostail decompressionschedules since the early 1920's,by incorporatingthe Dopplermeter silent bubble research done by Dr. Memll Spencer. In designingtheir standard decompression schedules, the U.S. Navy constructed a mathematicalmodel basedon 6 different "tissue" compartments.When it came time to figurerepetitive dives, there were so many possible combinations of dive time,maximum depthsand surface intervals that the immense number of calculationsrequired made it impracticalfor theinto continueusing all 6 compartments.As a result,repetitive diving with theNavy tables is basedon a mathematicalmodel for a singlecompartment. You must rememberthat these tables were designedbefore the computerage. Use of a single compartmentwas the easiestand most practical way to devisea repetitiveschedu1e that was a fairly low priority, and for an organizationthat had a massiveroster of divers to call upon.

The SuuntoSME-ML calculationsare always based upon a mathematicalmodel that contains9 compartments,the 6 compartmentsfound in theNavy tables plus 3 additional compartments.In addition,the SME-ML produces half timesranging from 2.5minutes to 480minutes, in comparisonwith theNavy tables' 5 to 120minute half times.This expands the rangeand makes more conservative the mathematicalapproximation of 's body,and still appliesboth to repetitivedives and to first,or single,dives. The SME-ML's "low bubble"no-decompression limits, by design,allow less nitrogento buildup in thecompartments than the U.S. Navy tables. Each compartment has a reducedMaximum Allowable M.A.P, or "M" value}which reflects a more conservativeestimate of thebody's ability to holdexcess nitrogen upon surfacing. An excellentexample of this is the no-decompressionlimit for the first dive to 60 feet: the U.S. Navy tables allow 60 minutes at 60 feet and the SME-ML allows 53 minutes at 60 feet.

50 Coley,Olivef and Nikkola: The Snnnto S ME-ML:Computer assisted multi-level diving

Moreimportantly, the SME-ML incorporates a slower ascent rate, 33 feetper minute,to permit a moregradual release of excessnitrogen as the diver ascends. If a diver using the SME-ML ascendsfaster than 33 feet per minute, the "SLOW" warningwill blink on the diving display. Thediver can slow down or stopcoming up until the "SLOW" warning disappears, aslong as he does not ascendabove 10 feet. If "SLOW"is still flashingat 10feet, the diver muststop there until it goesoff. Shouldthe diver surface with the "SLOW" on deflinitely not a recommendedpractice!, the "SLOW"warning will remainon until thenext dive, or until the unit shutsdown - a reininderfor the diver to adjustascent rates an instructorcan easilysee who is havingproblems in thisarea and work with thoseindividuals!. Our numberone goal in designingthe SME-ML was to presentthe diver with all of thisvaluable information in a straightforward,easy to readdisplay. One that would only show the information that was significant at a given moment. The Suunto SME-ML featuresan unclutteredscreen that only displaysdiving informationwhile the unit is underwater,and surface/diveplanning information while it is on the surface.

Next we thought that it was very important to eliminate the need for external switches.No externalswitches means no holesin thehousing that might cause the DC to flood. Regardlessof this benefit,it was the fact that we did not want the DC to be switched off eitheraccidentally or in uneducatedattempts to prolongbattery life! while it wasstill calculatingresidual nitrogen levels between dives, that leadto the developmentof the rubbercontacts that activate and recall the dive profiles. Simply stated, the SuuntoSME- ML can not be turnedoff during a repetitivedive series. The surfaceinterval display of the SME-ML automaticallybegins to showdive planninginformation to helpplan the next dive at the end of thedive just completed.As the surfaceinterval increases,so doesthe availabledive time for the next dive, basedon the residualnitrogen level in eachof the 9 compartmentsthe SME-ML usesas a modelfor its calculations.

The SME-ML continuesto trackresidual nitrogen in all 9 compartmentson the surfaceunti1 they no longeraffect no-decompression limits. It automaticallyshuts down whenall 9 compartmentsare "clean" of residualnitrogen. It is notat all uncommonfor an SME-MLto remainon muchlonger than the standard12 hours the Navy tablescall for, particularlyif you havebeen diving heavily. SeaQuest and Suunto saw the need for whatis in essencean underwaterflight recorder.A memorycapable of recordingprecise data, an exact dive profile.We realized how quickly maximumdepth and total dive time would becomeinsufficient information whentrue multi-level diving techniqueswere applied. How canyou explain a maximum depthof 110feet with a totaldive time of an houror morewhen only this simplistic information is available?! TheSuunto SME-ML features the ability to recallup to tenhours of divetime, and displayit in 3 minuteincrements. This information can be easily organized into accurate diveprofiles that graphically display a diver'strue exposure at various depths. Diveprofiles are extremely helpful in postdive debriefings. Did thestudent execute thedive plan for thisdive? Did a studentexceed the maximum depth limit setfor thisdive? Did the studentmake a safetystop at theend of this dive?The many applications of the "underwaterflight recorder"function of the SME-ML arejust startingto be understood.It

51 Langand Hamilton Eds.!:AAUS DC lVORÃSHOI'.U.S.C. Sea Grant Program, Los Angeles,CA, 1989 is a newtool for a newera in diving.Part of thechallenge and part of the excitementof introducingthese new concepts into diving instructionwill be the properapplication of these new tools. At thistime we all mustrealize the changes our sportis goingthrough and that it is up to us, as diving professionals,to masterthese new tools and techniquesso that we can sharethis information with therest of therecreational diving community. Decompression theory has always beena complexand fascinatingsubject. With sucha multitudeof new toolsand techniques, computer assisted multi-level diving is a subjectthat you could write a bookabout, and, in the processof creatingour supportprogram, we have. TheSuunto SME-ML is thestate of theart in divecomputers. We truly believethat. We want you to learn as much as you possibly can about decompression.We are convincedthat the more you know, the betterwe will do in the marketplace. The more you teach,the saferour sportwill become.

52 Session 2: Discussion

MANUFACTURER'S SESSION DISCUSSION

Discussion after John Lewis Johnwas asked to commenton thefact that the unit did notoutgas Lewis calls this "relaxation,"in referenceto themathematical exponential "decay" at a rateproportional to the differencein gaspartial ! at the surface.John pointed out that this function doesnot affect the behavior of theunit in multi-leveldiving, where it continuesto outgasin a mannerabout 10 fsw moreconservatively than the modelof the USN tables.

Discussion in manufacturer's session

[EDITOR'S NOTE: No paperswere receivedfrom Al Carpenter !,Mark Walsh !,or ChuckLocke U.S.Divers!, but sincethe presentations wexe made, we feelsoine discussion should be included. Chuck Locke provided the DC comparativetables in the appendix.]

Presentation by Al Carpenter

Al Carpenter is West Coast sales representativefor Beuchat USA. The dive computer sold by Beuchat in the U.S. is the same as the Aladin and Black Fox. Beuchat has no design or manufacturing function, and only distributes it in the U.S. as the G.U.I.D.E.The DC wasdeveloped in Switzerlandby theUwatech Co. This unit is based on theresearch of Dr. Biihlmann.It usessix compartmentsand has four setsof parameters for four different altitudes.First is sealevel to 2470 feet altitude, 2400 to 5100, 5100 to 8555, and 8555 to 13200. The unit senses the altitude. A big problemis that peoplehave trouble turning the unit on. You startit by dippingit in wateror by wettingyour fingersand touching the two contacts.It is now readyto go into the dive mode.You haveten minutesto get it into the wateror the unit will shutdown. If it doesshut off andthen you go into thewater, it will flashan error and you haveto go backand start over. It displaystwo rowsof numbersand letters and six group areas.A 3.6 lithium battery gives 5 yearsor 800 diving hours.It has 13 functions in the readout.The first is contactactivation. It will activateat 4 feetof depthand its depthis goodfrom 4 feetto 315fsw. It hasa maximumdepth indicator. You haveto comeup 4 fsw shallowerthan the maximum depth in orderto getit to lock on to themaximum depth. It showsyour remaining no-d time, flashing "deco warning" on a digitaldisplay. You have to stopat 10fsw stagesto 80fsw. As soonas you clear a depth,it clicksto thenext depth. If you passa stopcoming up, it tells you to go backto that stopand it locksinto that mode.It won't outgasat the surfaceif a stopis missed,it will just addon to the previousdive if you do anotherdive. It goesinto a tenminute surface interval modeafter a divein whichyou cannot access anything or changeanything. It is waitingto seeif youate goingto makeanother dive within 10min, in whichcase it will calculateit aspart of the previous dive. In other words, the minimum surface interval is ten minutes. Thereate two probes you can contact to accessthe log of thelast five dives.It gives you maximumdepth, total dive time and surfaceinterval time, This surfaceinterval would not last if you madea diveyesterday. There is a low batteryindicator, and the usercan changethe battery. You do howeverlose the memory when you changethe battery.It is

53 Langand Hamilton Eds.!:AAUS DC WORKSHOP.U.S.C. Sea Grant Program, Los Angeles,CA, 1989 sold as a console or as a wrist unit, at $699 and $450. There are two console models, a two-port and a three-port,which alsohas a compass,and there is an instructor'smodel.

Presentation by Mark Walsh MarkWalsh is theproject engineer for Dacha;responsible for theMicroBrain. This dive computerwas developedwith Divetronics,Switzerland. It usesthe P3 model,a modified version of the Buhlmann-HahnP2-3, with 6 compartments,from 4 to 397 minutes.It comesin severalconfigurations, wrist and console,and an instructor'smodel with a potentiometeron it for simulatingdives. There is alsoa simulatorprogram that runs on an Atari available to dealers and instructors. An IBM PC version is coming out in January.They have a user'sguide for dealersand instructors, but he mentionedthat they axenot an instructororganization and would like the input of the training agencies.

The MicroBrain runs from 0 to 330 fsw, and assumessea level to be 0.95 bar. It is altitude adjusting, from 0 to 4920 feet and from 4920 to 6560 feet. It has a range for equilibration,and it takesless time to equilibrateif you arealmdy partly at altitude.Above 6560feet it doesnot computeno-stop times because this is not well enoughknown, It then becomesa precisiondepth gage and bottom timer. It recordsthe mostrecent six divesin the last 48 hour periodand is consideredto be a ncxiecompressionand multi-level computer.It scrolls no-d information before the dive from 51 to 130 fsw in 10 fsw increments. It uses depthsof 51, 61, 71, 80, 90 and so on, due to rounding off of conversionsfrom metric. It doesno-d down to 250 fsw, where you get two minutes.While it is a no-decompression profiler, it does give you decompressioninformation. Ascent rate is 33 to 40 fsw per minute. It switchesfrom no-d time to decompressiontime required,with stopsto as deep as 100 fsw. It is a conservative model. If you missa stop,it givesyou a descentwarning, and takes you downto where you need to go to do your decompression.If you do not go down, or if you omit a decompressionstop, it goes"out of range".Another out of rangecondition is totalelapsed time of more than 199 minutes, in which case it shuts down for 24 hours. The "bottom time" is the total dive time.

It is encasedin sibconewith two three-voltbatteries soldered in place inside. It is supposedto be goodfor 10years at 100dives per year. If you needto sendit backfor a new battery,they will sendyou anotherunit andthen extract the electronicsfrom the gel of the former. It showsyour diving time as bars on a triangle, which gets smaller as your availabledive time is reduced.You activatethe unit to get the scrolling by touching the contactsand then you activateit whenyou beginthe dive by doing the samething. You can zerothe unit with a specialmagnet, allowing morethan one person to usethe sameunit. Of coursewhen you do this, you can'tdive againuntil the next day becausethe residualgas is lost.

Presentation by Chuck Locke CharlesE. Locke is managerof RAD for U.S. Divers, who market the Data Scan H. The Data Scan II is functionally the sameunit as OceanicDatamaster II, but has a slightly different display that showsthe sameinformation. In the consoleversion there is an algorithmfor managingair usage. Chuck mentioneddevelopment of a new unit. 'Iheir affiliate La Spirotechniqueis talking to Uwatech about a Biihlmann-basedunit, the "Monitor". Session 2: Discussion

A great deal more information aboutthis unit, and the othersas well, is given in a comparisonpn:pared by ChuckLocke andincluded in the appendix. The next question was for more information on the air consumptionalgorithm whichJohn Lewis, designer, responded to. It keepstrack of the breathingrate parameter which is consumptionnormalized at depth. If you double the atmosphericpressure, you doublethe consumption.It makesthat approximationso that alterationsin depth,are taken into consideration.It is a runningaverage of your particularconsumption.

Flying after diving

Most of the units have a "safe to fly" mode. Someone asked what criteria are used to be able to say this. The Suuntohas to outgasto a point less than 2 psi over . This was challenged by Mike Emmerman, who has data on a number of divers who have developedDCS in aircraft in a wide variety of gas loading statuses,even as much as 41 hours after a dive. The messageis, we probably do not have enoughdata to make this decision. Ralph Osterhout maintained, however, that we need some sort of criterion for this function, and this was agreed.

It was further pointed out that 12 hours is considereda safepost-dive time to go flying, but that it may take 19 to 20 hoursto clear the 480 minute compartmentdown to 2 psi over ambient.Flying as long as 5 daysafter extensivediving hasresulted in symptoms. Oneopinion is that calculationsof gasloadings may havelittle bearingon whenit is safeto fly. It is probablythe bubblesand how long they persist.

Dick Vann points out that we really cannotsay it is "safeto fly", that all we can do is choosean acceptabledegree of risk. How do we make this decision?There is no line between"safe to fly" and "not safe to fly". All we have is a gradualreduction of risk. Divers frequently, due to contingencieslike bad weather,will chooseto fly after a dive. They normally get awaywith it. Even thoughthere is no hardline, we feel it is necessaryto set some kind of limit.

Mike Emmermanhas gathered 47 caseswhere the diver hadbeen a "D diver" USN repetitive status,which is the point consideredsafe to fly! or better,for 7 to as many as 40 hoursbefore flying, did not showsymptoms before flying, but had symptomsin the aircraft or shortly after landing. There was not enoughdata to reconstructeither the dive profile or evena "body"profile of the person.

Ralph askedif DEMA might sponsordata collection, perhaps through DAN, to help get a database together. He feels sure that researcherslike thosein this Workshopcould make something of it.

Bill Hamilton reported a workshop held by the U.K. Diving Medical Advisory Committeeconvened because the helicopterpilots in the North Seawere concernedabout haulingdivers to shoreafter they had beendiving. When the groupwas askedfor data,the silencewas deafening.There were very few documentedcases to report. The workshop was swungby a reportof 15,000diver-trips following a rule of flying no soonerthan 12 hours after diving, with no reportedproblems. This doesnot mean 15,000divers flew 12 hours after diving, but that the rule had that data basebehind it. That rule was adopted. That group would not be specific aboutnitrox saturationdiving, but felt it shouldbe over 48 hours.

55 Langand Hamilton Eds.!: AAUS DC WORKSHOP.U.S.C. Sea Grant Program, Los Angeles, CA, 1989

TheWorkshop carried on to list thevalues for flying afterdiving of thevarious DC's represented here.

Computek: 2 fsw over ambient Digits 12 hrs after last dive Micto Brain: 0.58 barsas the ceiling SHnnyDipper. 2 fsw psi! over ambient Suunto: 2 psi over ambient Thevalue given by MaxHahn applies to theMicroBrain. Max explained that the lowestpressure one should encounter in a commercialaircraft is 0.65bars, and that having a ceilingof 0.58bars should be well within this limit this is about8,000 feet of altitude!. Thisis a ceiling,not the inert gas pressure in thetissue. This might take as much as 24 hours. Those DCs not mentioned do not have indicators. JohnLewis, whose DC does not have this function, suggests that to getgood data thiswill haveto bedone experimentally. Glen Egstvom notes that this will takesome years at best,but that it is acceptableto go on with the currentcriteria. Bill Hamiltonwarned that this talk illustratesthe in makingdecisions of this sort,that it is easyto getnarcotized by thenumbers and begin to believethem.

"Lockup" mode Thediscussion turned to themaximum depth allowed, with concern expressed by manythat the depths allowed are too deep.The values are in theAppendix. Some of the unitsgo "outof range"or otherwisestop working when the depth is exceeded.This 1ed to furtherdiscussion of thematter of theDC's shutting down when they might be needed most.One reason for thisis thatwhen the diver has "violated" in certainways, there is no goodalgorithm for gettinghim/her out of thatsituation with confidence. Example: When thediver omits a stopon ascent,the computer will seea fasteroutgassing, but what is more likely,is thatthe diver has provoked bubble formation and needs more time, not less, to get to the surface. In thecases where the DCs stop computing, they usually continue to providetime anddepth information and it is up to thediver to usethat to getto thesurface. A numberof suggestionswere made about how to handlethe violating diver. There seemedto be agreementthat the diver in this situationcannot go unpunished.It waseven suggestedthat the DC shouldshock the diver when he violates, or thatit should"break" or gointo a lockupmode that requires a $100repair bill to getit goingagain. While there was agreementthat the viohtion shouldbe punished,when to do it and how to do it was not agreedupon. Another ttung that was agreed by mostis thatwe prefer the DC's to continue to compute for the diver who has violated. Thereis a dilemmahere, because the focus of thethinking ranged from thenovice studentdiver to theexperienced scientific diver, and the viewpoints seemed to bereflected in thepart of theelephant touched by eachblind man. Some wanted the units not to go deeperthat 130fsw, becausethat is the"limit" for recreationaldivers, but therealities are thatthe reasons they buy the units is formore aggressive diving. A majortheme throughout this and other discussionsis the strong belief that the recreationaldivers needmore and bettertraining. Whether the DC's should limit theirdiving was not agreed on at all. Session 2: Discussion It waspointed outthat we were here with concern forthe scientific diver, who may diveto as deep as 190 fsw, if qualified,and his DC should dothe job. But scientific divers alsooperate under a muchhigher order of discipline and are far more diligent about obeyingtherules, since there isa lotat stake. Even so, the entire diving community will notethe conclusions of this Workshop. Therewas of course a plea tostandardize thecriteria for the "lockup" mode. The Workshopdidnot do that, instead charged themanufacturers withproviding some means ofgetting outof these violation situations, andto not have the DC stop computing.

Units Whenthe matter of unitscame up, Bill Hamiltonpointed out that one cannot correctlyuse the linear conversion factors between feetand metres asunits of length when pressureis the parameter involved, because the definitions are different:

One msw = 1/10 bar= 10kPa Onefsw = 1/33standard atmosphere = 0.030705 kPa Thereforethe conversion between the pressure units is One msw = 3.2568 fsw

One fsw = 0.30705 msw

57

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