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tech talk

Text by Mark Powell “Plan the dive and dive the plan” has long been the mantra employed in all areas of diving. Technical divers in particular spend more time planning their dives than many recreational divers. This is due to a number of factors, including increased risks, greater depths, high gas usage at depth, increased obligations, increased toxicity load- ing and a host of other reasons. For many recreational divers, has become a lost art, but technical divers still place a large emphasis on the The Evolution of value of dive planning. Despite this, the methods of dive plan- ning have changed to take advantage of changes in tech- nology and equipment. In this Dive Planning article, we will look at how dive ANDREY BIZYUKIN planning for technical divers has In the early days of , a dive was to look up a decompression very earliest technical divers had to use The decompression schedule would be evolved and how we can best there were no PC planning tools or dive schedule using pre-generated tables. tables or work directly copied out on a dive slate with fixed make use of modern technology computers suitable for technical dive Initially, not even the pre-generated with decompression researchers if they decompression stops and run times. while still maintaining safety. planning. The only option for planning tables were publicly available, and the wanted to obtain a set of tables. Central nervous system (CNS) and oxy-

76 X-RAY MAG : 86 : 2018 EDITORIAL FEATURES TRAVEL NEWS WRECKS EQUIPMENT BOOKS SCIENCE & ECOLOGY TECH EDUCATION PROFILES PHOTO & VIDEO PORTFOLIO Using a PC plan- ning tool to gener- tech talk ate a dive plan (left)

Pre-printed decompression tables (below) However, as computers become more common, reliable and affordable, this gradually changed. Divers would still use a planning tool to generate a decom- pression schedule to write on their slate just as before. The change was that this schedule was now used as a backup to the computer, which became the prima- ry method of running the dive. Despite this, the plan would still primarily be pre- determined in terms of a fixed bottom time, in order to still be able to fall back on the written plan. However, the actual ascent time would now be determined by the deco schedule on the computer. Now computers are much more avail- PHOTO COURTEISY OF MARK POWELL Backup plans Personal computers In time, personal dive comput- would also be With the increased availability of person- ers became available that could prepared just in al computers, it became feasible to gen- handle decompression diving, tri- case erate custom tables using a PC planning mix or , but they were goes slightly tool. This allowed divers to use a number still expensive and often unreli- deeper, stays of different gasses, decompression mod- able. As a result, it was common slightly longer els and conservatism settings. The overall to use a written plan on a slate or, in the worst process of planning a dive remained the with a computer as backup, in case, goes same, just using a planning tool instead case of going off the plan or in both deeper of tables. The planning tool would gener- case of an emergency. and stays ate the decompression schedule, CNS This was not an ideal situation longer. With and OTU loadings as well as gas require- as divers would have to spend pre-prepared ments. The only difference would be that a significant amount of money decompres- the PC planning tool would do the labori- on a without sion tables, ous arithmetic required to calculate gas being able to make full use of it. “slightly deep- requirement, CNS loading, etc. rather This led to the difficult situation

PHOTO COURTEISY OF MARK POWELL MARK OF COURTEISY PHOTO er” was usu- than the diver doing it by hand. When in which divers would have to ally taken to mean the used correctly, these PC planning tools forego the flexibility offered by gen toxicity units (OTU) load- next depth increment, which on many removed the risk of the diver making a the dive computer and stick to a ing would be calculated by hand. Gas tables was 3m or 10ft deeper. “Slightly silly arithmetical error. The computer-gen- fixed depth and time in order to usage would be calculated for each longer” would be taken to mean any- erated schedule would then be trans- be able to fall back on their writ- phase of the dive and the thing from three to five minutes longer. ferred to a slate just as when the plan ten backup plans in the case of was used to add in a safety reserve. The Finally, a backup plan would also be is generated by hand. In the water, the a computer failure. This difficult dive would then be executed by follow- prepared showing the decompression dive would be executed in exactly the decision made many divers and ing the dive plan run times written on the schedule if the divers lose their decom- same way, with divers using their bottom agencies question the suitability slate, with depth and time being moni- pression gas and have to complete their timers to monitor the run times written on of dive computers for technical tored using a bottom timer. decompression using back gas. the slate. diving. START HERE

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PHOTO COURTEISY OF MARK POWELL ANDREY BIZYUKIN Using slates and wetnotes for dive plans (above); Technical diver with a (top right)

able and reliable. In addition, This is where a shift in the required in litres. Finally, we can the costs have reduced so much approach is required. Let’s con- then convert this into a bar pres- DIVE PREPARED. that many people have backup sider the point of gas planning: sure by dividing by the size of your BECAUSE NO ONE KNOWS THE FUTURE. computers. The flexibility offered It is to ensure we do not run out cylinders. No matter how much you train or how well you plan, accidents can still happen. And there is by the computer is in contrast of gas, even in an emergency Let’s say that after performing no crystal ball to predict when you may find yourself facing an emergency. The smart to the rigid nature of tables. situation. Specifically, we want this calculation, we know that our is to make sure you and your family are protected against the unforeseen. Unfortunately, when your backup enough gas to get ourselves and minimum gas is 70 bar. This means DAN’s Dive Accident Insurance exists for those “just in case” moments. is based on written tables you our buddy to the surface, or to that at any point in the dive, as cannot make full use of this flex- the next breathable gas source, long as I have at least 70 bar, I ibility. However, when you have a even in a stressful situation. This is know I have enough gas to get backup computer, suddenly this known as minimum gas. to the next source of breathable flexibility comes into its own, and We can calculate our minimum gas, even if my buddy has a cat- this is where significant changes gas in advance for our maximum astrophic gas loss. Once one of us to planning styles started to be planned depth. This is based on reaches 70 bar, we must then start

adopted. combining the rates the ascent. Using minimum gas 44% of our buddy and ourselves and rather than fixed usage gives us Significant changes then doubling this figure to take the flexibility in back gas planning When you have a fixed decom- into account the stress of an out- to match the flexibility in decom- 2016 SMALL COST. BIG BENEFIT. pression schedule, working out of-air emergency. This is then pression schedules provided by Dive Related DAN’s Dive Accident Insurance benefit Illness/Injuries 9% provides coverage of up to $500,000 for the gas usage for that schedule multiplied by the time it will take the dive computer. (Cases / %) medical dive accident expense and pays Other is very straightforward. The dis- to start the ascent and ascend to 100% of eligible expenses. Considering a diving-related injury or illness can set you advantage of having flexibility in the first gas switch stop. Decompression stops 28% 2% 2% Non-Fatal back thousands of dollars, it pays to be prepared. the decompression schedule is it We can then multiply this Minimum gas calculations will Decompression 9% 2% Pulmonary Edema - IPE now becomes impossible to cal- by a figure to account for the cover the gas required to get Sickness 2% Fatality 2% Arterial Gas Embolism (AGE) culate exactly how much will be increased at depth to to the first gas switch, but what Marine DAN.org/JOIN required in advance. give us the total volume of gas about the gas required for the Envenomation

Feb_2018_HalfPg_3.9X10.2_Gold_DivePrepared.indd 1 1/31/18 1:41 PM 78 X-RAY MAG : 86 : 2018 EDITORIAL FEATURES TRAVEL NEWS WRECKS EQUIPMENT BOOKS SCIENCE & ECOLOGY TECH EDUCATION PROFILES PHOTO & VIDEO PORTFOLIO For decompression stops, the traditional approach has been to work out exact- ly what is required and see how much is available, and ensure that the amount tech talk required, plus a contingency, is less than the amount available. The alternative is to use a planning tool to find the maximum amount of decompression that Dive Planning can be done on the gas available, without exceeding the safety reserve.

you only need to calculate these can be considered as a second- is likely to be scrubber duration numbers once for any given dive ary consideration to the real limit- or CNS limits that will determine depth. With a PC planning tool, ing factor. the maximum length of the dive. it is very easy to calculate these The only time that gas usage two numbers for a range of dive Rebreathers becomes an issue is in the case depths. This can be turned into a The discussion above has mainly of a bailout where gas availability table in your wet notes that then been concerned with open becomes critical. contains all the required informa- circuit diving, but CCR diving In reality, it is the bailout scenario tion you need for dive planning. has progressed along a similar that will normally be the limiting For most dives, it will be gas path. Modern rebreathers almost factor for most CCR dives. This usage, either backgas, deco gas always have a built-in decom- means that bailout planning will or, in the case of CCR, bailout pression computer integrated determine the limits for TTS. This is gas, that will determine the limits into the handset, and most divers done by using a planning tool to of the time. Other factors such as have a backup computer. calculate the maximum CCR bot- CNS should also be considered, However, gas planning is very tom time that can be done without but when the dive plan is gener- different on a rebreather, com- then exceeding the available bail- ated using the PC planning tool, pared to open circuit. A CCR has out gas, when the diver bails out at the CNS can be reviewed and, almost unlimited gas and, if noth- the end of the planned CCR bot- provided it is well within safe limits, ing goes wrong with the CCR, it tom time. The CCR TTS at this point

ANDREY BIZYUKIN decompression stops? The tradi- surface can be done within the is around the target depth, the tional approach has been to work gas available. This means that as divers just need to monitor their out exactly what is required and long as the total time to surface available gas and their time to see how much is available, and is less than this maximum amount, surface. The actual bottom time ensure that the amount required, you know you have enough gas becomes less important. The dive plus a contingency, is less than available. is terminated when either of these the amount available. Putting these two concepts limits is reached: either the avail- The alternative is to use a plan- together, the procedure is to first able gas reaches the minimum ning tool to find the maximum calculate the longest dive that gas limits, or the total TTS reaches amount of decompression that can be done at the target depth the maximum amount. can be done on the gas availa- within the decompression gas If one dives with a regular ble, without exceeding the safety limits. This can be used to find buddy and always use the same reserve. You now know that you the maximum time to surface size cylinders and the same gas can do this amount of decom- (TTS). We then calculate the mini- mixtures, then this means that the pression, and this can be con- mum gas required to get divers minimum gas and time to surface verted to a total time to surface. and their buddies up to their first will always be the same for each Again, you know that this time to gas switch. Provided the dive dive at that depth. As a result,

Depth (m) Minimum Gas Time to Surface (TTS) 45 70 62 minutes 50 75 64 minutes 55 80 67 minutes 60 85 72 minutes

Sample dive planning table showing minimum gas and TTS for a range of depths. Note these are not real numbers ANDREY BIZYUKIN and should not be used for dive planning. Technical diver with a rebreather

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Author and technical diving instruc- tor Mark Powell ready for a dive.

becomes the end point of this dive, as we know that as long as we stay within this CCR TTS, the correspond- ing bailout ascent is achievable with the bailout available.

Overhead environments DEMA SHOW 2018 Overhead environment diving also NOVEMBER 14–17, 2018 | Las Vegas Convention Center | Las Vegas, NV introduces a number of other fac- tors. For cave and wreck penetra- tion, the minimum gas and time to surface calculations will have to include the time required to exit the overhead environment as well as the time to ascend, and so the planning becomes more compli- cated. For more advanced dives, when the depths are greater than 80m, more planning factors come into play. Team logistics become PHOTO COURTEISY OF MARK POWELL the more important factor and, although time to surface and mini- TTS and minimum gas approach. of the flexibility offered by modern IN OPPORTUNITY mum gas calculations can still be Using TTS or minimum gas does dive computers.  JOIN US AT THE WORLD’S PREMIER INTERNATIONAL TRADE-ONLY EVENT used, there are a whole range of not remove the need for planning. FOR DIVING, ACTION WATERSPORTS AND TRAVEL PROFESSIONALS. additional factors, such as the use You still need to do the planning Mark Powell is one of the leading Connect with thousands of industry professionals who direct, infl uence and recommend purchases of support divers, surface support in order to know your minimum technical diving instructors in the for their organizations. Discover fresh technologies and products, explore new possibilities, emergency planning. gas or TTS, but the details of the field. He has been diving since build a worldwide professional network and surround yourself with opportunity. Technical training tends to fol- decompression profile can be cal- 1987 and instructing since 1994, low the evolution above with new culated “on the fly” by the dive and is a full-time technical diving divers starting with written plans, computer. By understanding the instructor trainer and a member generated from pre-printed tables minimum gas and time to surface of TDI’s Global Training Advisor REGISTER AT DEMASHOW.COM or PC planning tools. This ensures concepts, the combination of Panel. He teaches all levels up to that the diver understands the dive planning using a PC planning and including Advanced Trimix ENTER VIP CODE: XRPA18 principles behind decompression computer and the use of a dive Instructor. In addition, he has led schedules and gas planning. It also computer to intelligently manage a number of expeditions to vari- ensures that the diver can man- the execution of the dive provides ous parts of the world, including age ascent rates and display the the best of both worlds. The dive is the Middle East, Costa Rica, Malta discipline required to follow the still planned to ensure more than and the Red Sea, but is usually dive plan on the computer accu- adequate safety. Divers still have found diving the wrecks around In partnership with rately. The diver then moves on to to understand the details of their the coast of the United Kingdom. using dive computers with tables dive plans and should not “blindly” For more information on any on a slate as a backup before follow their dive computers. But at aspect of technical diving, visit: eventually planning by using the the same time, they can make use Dive-tech.co.uk.

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