WARNING: This program is written for the sole purpose of experimenting with various concepts in decompression theory. It is not meant to be a real dive planner, and probably contains dangerous bugs and errors.

DO NOT USE THESE RESULTS FOR DIVE PLANNING

Notes:

DepthPlanner has numbers of decompression models and conservatism options far in excess of any other decompression software. This is for the purpose of experimentation. One can compare many different decompression models and schedules quickly and easily. Many of the decompression models are of purely historical interest, while others are mainstream and current, and some of the conservatism options are the latest thinking. There are no "bubble models" here, at least not yet. In my opinion they have too many arbitrary assumptions and fudge factors, and too much complexity to be worth the considerable trouble it would take to get one working.

The program interface is divided into several panels of user-selectable options. The interface is primarily point-and-click, allowing for quick what-if type analysis. Results are displayed in the box immediately below the user interface. I think this is the best and easiest to use of any decompression modeling software I have seen, and I've seen a lot of them. Some of even the expensive commercial programs have interfaces so bad that they are almost unusable. There are no fancy graphics here, all inputs are specified as numbers, and all results are displayed as printable text tables.

The program implements all three versions of Buehlmann's ZH-L16 algorithm, as well as the compartment 1 / 1b option. This is the most widespread and widely accepted decompression algorithm. This particular implementation utilizes the closed-form solution to the Shreiner equation, rather than messy slow numerical integration. It is therefore very fast and efficient, and avoids the cumulative calculation errors of many other programs. Whether or not I really got it right is another story, however - DepthPlanner may just be quickly calculating very precise wrong answers - no amount of testing will ever make me 100% certain.

All program inputs are rounded to the number of decimal places shown in the default values before any calculations. Specifying more decimal places than shown is simply false precision. The user may optionally add a Note which is appended to the program header. Note could contain name, date, purpose, etc. In the program output, all times are rounded up or down to the nearest minute. This is merely for formatting purposes, but it can result in some anomalies, such as apparently instantaneous ascents during decompression. This is no cause for concern - the program carries time in full precision during all calculations.

DepthPlanner is optimized for the type of diving I do, under the conditions that I expect, with the equipment I would use. That is to say, it is for Northeast wreck diving. Therefore, it defaults to sea level, salt water, unlike some other expensive decompression programs which annoyingly insist on cave diving conditions. The program will automatically handle a single bottom gas and up to three decompression gases, equating to a set of tanks on your back and one or two stage bottles - a typical Northeast rig. More complex schedules, as for extreme deep technical dives or cave dives, can be input and processed manually.

DepthPlanner calculates oxygen exposures, but does not calculate O2 credits for surface intervals.

The program itself is written in Perl, and is, to my knowledge, the first and only web-based decompression software in the world. Nonetheless, it is not for public consumption, and will not function without the current password, which is given out only to people I know and trust. If I don't know you personally, don't bother asking, and if I gave you the password, please do not give it to anyone else. I don't need any lawsuits !

Waypoints

Dive Waypoints are entered in the following formats:

Depth  Time
Depth  Time  FO2
Depth  Time  FO2  FHe

Each waypoint is 2-4 items separated by spaces. One waypoint per line. Blank lines are ignored. Users are limited to 50 waypoints per batch. Depths are in feet and max depth is approximately 420 feet. Times are in minutes. There is no time limit, although very long decompression times may cause program abort.

Gas mixtures are specified as decimal values between  0.00 and 1.00. Gas values are optional. If the helium specification only is omitted from a waypoint, it is assumed to be Nitrox, with 0.00 helium. If neither oxygen nor helium is specified, the program defaults to the values at the previous waypoint. If the oxygen specification is omitted from the first waypoint in a dive, it is assumed to be air. In other words, Trimix and Heliox must be specified with the full four items. Nitrox and air may be specified with three items. If this is confusing, just specify everything to be on the safe side.

PO2 at any stage in a dive is limited from 0.12 to 1.65 Atm. PO2s outside this range will cause an immediate program abort. Minimum FO2 is 0.05. There are no enforced limits on helium or nitrogen - so you can narc yourself to heaven.

By default, all waypoints in a series are assembled into a single multi-level dive. To create repetitive dives, insert a waypoint with a depth of 0 and the desired surface interval. Surface intervals default to air, regardless of the gas specified. ( To simulate a surface interval on O2 or any other mix, enter a dive with a depth of 1 foot. )

To reinitialize the algorithm between dives, as for creating dive tables, insert a waypoint of -1. Manual gas switches may be inserted with zero-time waypoints if desired. Gas switches are assumed to be at the end of an ascent or the beginning of a descent. See Decompression below.

Rebreathers have a few extra options. To simulate open-circuit bailout on a rebreather dive, insert a waypoint of -2. To override the high O2 setpoint of a CCR, add the new setpoint as a fifth waypoint item. The new value will hold for the remainder of the dive, or until it is replaced by a value in a subsequent waypoint. This has no effect on the low O2 setpoint.

Comments may be inserted by placing a single quote at the beginning of a line:

' comment

Each dive will generate an output similar to the following. This needs little explanation.

Vol = gas volume, in cubic feet

Not shown here is an additional column of miscellaneous notes for each waypoint in the dive.

In addition to the dive profiles, all other relevant input parameters are echoed back in a single header section, similar to the following:

Table Generator

The Table Generator option will automatically create a decompression table for the given input parameters. These are fairly self-explanatory: a single depth and bottom mix is chosen, and dives of varying length are simulated and assembled into a concise table, as shown below:

The top row is planned bottom times, and the first column is depths. To use the table, go down the first column to the bottom depth ( x'ed out here. ) then move across to the column representing the planned bottom time. From there, you proceed up the column to each decompression stop. Times are ending run times - the time at which you finish the current stop and move to the next. So for the 25 minute dive, you leave the bottom at 29 minutes, and proceed up to the first stop at 110 ft, leaving there at 32 minutes for the next stop at 80 ft, and so on. The 0 feet or surface level shows the total dive run time.

Gas mix at each stage is shown in the right-most column, and other useful information is tabulated below each dive column. Tables may also be generated showing actual deco stage times. This does not generate usable dive tables, but is convenient for comparative purposes.

The Net Bottom Times option will subtract descent times from bottom times. This makes it easier to compare results with published tables that may have been generated this way. This option also affects user waypoints.

Open-Circuit Bailout is a rebreather option that will switch to open-circuit on the specified diluent at the end of the bottom time. It has no effect on open-circuit dives, or user waypoints.

Equipment & Environment

Altitude needs no explanation, nor does "saltwater".

Three types of scuba equipment are supported:

Open Circuit, or regular scuba tanks and regs, is the default. When Open Circuit is selected, gas percentages specified in Waypoints or the Table Generator are for actual breathing gas. SAC is your surface air consumption rate, in cubic feet per minute. SAC is used to estimate gas consumption. The default value is a good guess if you don't know yours. Smaller persons and women may want to use 0.6, and big people could use 0.8.

SCR stands for Semi-Closed Rebreather. When SCR is selected, gas percentages specified in Waypoints or the Table Generator are for breathing gas. Flow is the mass flow rate of the rebreather orifice, in liters per minute.O2 Rate is the user's O2 consumption rate, also in liters per minute. The default value is a good guess if you don't know yours. These values are used to estimate steady-state mix percentages and gas consumption. If a decompression gas is selected, open-circuit decompression will be used when possible.

Warning: there is no way to accurately predict breathing gas fractions for a semi-closed rebreather. Therefore, there is no way to calculate accurate decompression schedules for a semi-closed rebreather, and the profiles generated here should be considered no more than rough estimates.

CCR stands for Closed-Circuit Rebreather. When CCR is selected, gas percentages specified in waypoints or the Table Generator are for diluent, and actual breathing mix is calculated based on the PO2 Setpoints. The low Setpoint is used at depths shallower than the split depth, while the high Setpoint is used at depths greater than the split depth.O2 Rate is the user's O2 consumption rate, in liters per minute. The default value is a good guess if you don't know yours. This value is used to estimate gas consumption. If a decompression gas is selected, open-circuit decompression will be used when possible.

Models

DepthPlanner has a wide array of decompression models to choose from. All models run within the same neo-Haldanian framework.

Buehlmann's 1990 ZH-L16B model is designed for pre-dive planning, and is the most widely used  decompression model in the world. The ZH-L16C version is designed for real-time use in dive computers, and is slightly more conservative. None of the ZH-L16 models are today considered adequate without additional conservatism factors.

The 1983 ZH-L12 model is an earlier version based entirely empirical observations. It is more conservative than the later ZH-L16 models, and excessively conservative with regard to helium. I have pretty good faith in DepthPlanner's implementation of all of Buehlmann's models, for all gas mixes.

Workman's 1965 model is the earliest of all the modern decompression models presented here. DepthPlanner's implementation appears to be sound: despite its age, Workman's model produces similar results to Buehlmann's later models, even for helium mixes.

The following models are listed under Expert Options because they are incomplete and/or possibly wrong, or simply should not be used:

The ZH-L16A version of Buehlmann's algorithm was the prototype for the other two, and is not considered safe for real use, despite the fact that the differences between all three of Buehlmann's models are negligible once they are chopped-up into a stepped decompression schedule.

Haldane's original 1908 model is the earliest of all decompression models. It is based on five tissue compartments: 5-10-20-40-75 and a constant allowable over-pressure. By default, the model here uses a dangerously high value of 2.0. Use the MaxPR factor to throttle it back to Haldane's final 1.58, or any value you would like to try. At 1.58, Haldane's model turns out surprisingly conservative results for short dives, despite the fact that the it is not considered safe for real use. For long exposures, this becomes quite clear. If Haldane had simply included longer tissue compartments, his model would have been much more realistic. The second Haldane option explores this possibility, with extended tissue compartments and a reduced pressure ratio of 1.58.

The US Navy model of 1955 is interesting for the short and risky schedules it produces - even shorter than their dive tables ( which have clearly been tweaked in the most dangerous cases. ) The first Navy option is purely mathematical. while the second is based on empirical data.

My DCAP model is incomplete. At present I am missing the helium compartment half-times and other details of the algorithm. For the moment, the missing information has been estimated, and I have assumed that DCAP uses the same basic algorithm as Buehlmann and the rest. DCAP has a much greater level of conservatism built into it than any of the other models, for example, automatically generating deep stops for all dive profiles. Therefore, all conservatism factors are disabled with DCAP. The first DCAP option treats helium as slow - the same as Nitrogen. The second DCAP option treats it as fast, as with Buehlmann. The first option appears to be more correct, but results for helium mixes should not be trusted. I really want to get this working.

Both of my DSAT models are completely experimental implementations. They sometimes agree surprisingly well with the PADI RDP, sometimes not. The DSAT algorithm is strictly no-decompression, and somewhat different from the rest, requiring some special-casing in the code. During surface intervals, the DSAT model estimates offgassing using only the 60 minute compartment. This is not implemented in DepthPlanner, and there may be other differences as well. Conservatism factors are disabled with DSAT. The first DSAT option uses 7 tissue compartments, the second uses 14.

Conservatism

This is where things get interesting. DepthPlanner offers a bewildering assortment of conservatism options for you to experiment with. Each is selected or disabled by the check box, and any or all may be used at once:

GF-high serves two purposes in DepthPlanner. If used alone, it is the standard Buehlmann conservatism factor. Mathematically, it specifies how far into the "decompression zone" you are willing to go. 0.20 follows as close to the decompression "floor" as is likely to allow ascent, resulting in unrealistically long deco times, while 1.00 goes all the way to the limit of the model, ie no conservatism at all. Decompression stops regulated solely by this parameter are noted as "GF-hi Stops" in the program output. GF-high is limited to values between 0.20 and 1.00.

GF-low is similar to GF-high. If used alone, it behaves exactly as GF-high, and has the same limits. Like GF-high, extremely low values of GF-low will result in unrealistically long decompression times. Decompression stops regulated solely by this parameter are noted as "GF-low Stops" in the program output.

When used together, GF-high and GF-low become the high and low factors in the Baker Gradient Factor method. In this method, the actual conservatism factor used at any depth lies somewhere between the two, starting out on the first ( deepest ) stop equal to GF-low, and gradually changing to GF-high by the last stop. The effect of this is to generate relatively brief deep stops, without grossly exaggerating shallow stops. Decompression stops regulated by the Gradient Factor method are noted as "GF Stops" in the program output.

MaxPR is my own idea for limiting worst-case tissue compartment over-pressures during ascent. PR stands for Pressure Ratio. This harks back to Haldane's original ideas, and a value of 1.6 approximates Haldane's theory that bubbles form when pressure ratios exceed 1.58 ( which is no longer believed to be correct. ) Values may range from 1.2 to 2.1. The difference between MaxPR and Haldane's original theory is that MaxPR will at no time violate the other decompression constraints of the model used, whereas in Haldane's model, it was the decompression model. MaxPR may be used to generate deep stops: the smaller the ratio, the deeper the stops, although this may extend shallow stop times excessively. Unchecking the MaxPR box causes MaxPR to be ignored. Decompression stops regulated by this parameter are noted as "MaxPR Stops" in the program output.

Pyle is an implementation of Pyle's simple in-head calculation for deep stops. Pyle stops tend to be very deep, below what any of the other conservatism factors will reasonably generate, with the exception of ZH-L17TS. You may specify a time between 1 and 10 minutes for Pyle stops. Decompression stops regulated by this parameter are noted as "Pyle Stops" in the program output.

ZH-L17TS adds a "17th" ( actually, "n+1th" ) compartment to any decompression model. This compartment is unnatural, having some very fast characteristics, and some very slow ones. The result is that it generates deep stops, but does not otherwise affect the decompression schedule. The actual ZH-L17TS algorithm is proprietary, so I guessed a nitrogen half-time of 1 minute, and used the a/b factors from the slowest compartment, with pretty good results. Although ZH-L17TS is designed for use with the ZH-L16 models only, you may apply it to any decompression model in the program, although it is not effective on some of them, while others go haywire. Decompression stops regulated by this parameter are noted as "Z17TS Stops" in the program output.

The five conservatism options are fairly independent of each other, and may be mixed and matched together, sometimes with strange results. At any stage in a decompression schedule, whichever of the selected conservatism methods is strictest becomes the active one. In fact, you can create schedules with so many stops that you may never get out of the water - the results of most combinations are often too conservative to be useful. This compatibility chart might help you get started:

Decompression stops determined with no conservatism factor applied are noted as "Norm Stops" in the program output.

My 2 Cents:

Proponents of the ZH-L16TS method criticize Baker's method as a mathematical hack to the algorithm, something with which I agree, and it is an ugly hack at that, and not entirely easy to program. However, the ZHL-17TS method strikes me as pure voodoo, a mathematical quirk with no basis in the real world. It is therefore just as much a hack. Pyle's method is yet another hack, and an oversimplified one at that. So none of these conservatism methods is very appealing from a modeling point of view, but all work quite well in the real world.

The MaxPR method of conservatism is a very simple modification that works within the algorithm, requiring only one or two extra lines of code. At a setting of about 1.6, it generates moderately deep stops while extending shallow stops for extra safety. It is also quite compatible with the other methods of generating very deep stops.

Much of the difference between the various models gets lost when all the smoothness of Haldane's  exponential ongassing/offgassing model is chopped up into discrete one-minute time steps and 10 foot stop depths. Much of the apparent precision in the results is overwhelmed by real-world uncertainties. Decompression modeling is much more of an art than a science.

Expert Options

A number of decompression models are listed here, because they are not suitable for real-world use, but are of historic interest.

In general, you should leave the following parameters at their default values:

The Z1 / Z1b option selects between a 4 minute or 5 minute fastest tissue compartment for the ZH-L16 models only. Most decompression modeling is done with the 1b ( 5 minute ) compartment. This has little effect, except in extremely short bounce dives.

RQ is Respiratory Quotient, and may be varied between 0.8 ( Shreiner's medical value, conservative ) and 0.9 ( US Navy value for divers, liberal. ) It has very little effect. Unchecking RQ has the same effect as setting it to 1.00.

Disabling H2O Effects is useful when comparing results to older decompression programs that do not model alveolar water vapor effects, like Zplan. Unchecking H2O Effects  has a slightly conservative effect, but for accuracy you should leave it enabled.

Disabling He Effects causes the program to base its decompression schedules on Nitrogen M-values alone. Effectively, this causes Helium to on-gas at its own (faster) rate, but off-gas at the same rate as Nitrogen, which will have very a conservative effect on helium mixes, but no effect on non-helium mixes. Some decompression models do this by design, and some older softwares may do this also.

Decompression

Decompression stop options default to the most commonly-used values. However, if you wish to experiment, you may try a range of options. Unreasonable decompression stop options may interact with conservatism settings to prevent the program from reaching a solution, so some common sense is required here.

The program may optionally use up to three decompression gases, which will be automatically switched-to at the proper depth during a decompression schedule. If selected, the Max Gas Switch Depth option prevents deco gas switches from being made deeper than the specified depth, regardless of PO2, equipment, or mix. This can be used to conserve deco gas on deep stops, or to avoid using deco gas inadvertently on shallower dives or with a rebreather.

If you would require a more complex decompression schedule, you may disable all automatic decompression settings and enter decompression stops and gas switches manually as waypoints. ( It is not possible to disable automatic decompression stops with the table generator. ) When entering manual decompression stops, if a waypoint time of -1 is used, the program will calculate the necessary decompression time for you, based on whatever conservatism factors you choose. Otherwise, you may specify your own decompression times, and the program will run your hand-made decompression schedule and inform you if you survived or not.

"-1 time" waypoints are converted to zero-time waypoints if automatic deco scheduling is re-enabled. Needless zero-time waypoints are suppressed from the program output.

Disabling decompression stops disables Pyle and ZH-L17TS deep stops as well, but GF-factors and MaxPR may still be used, as described below:

If a decompression violation occurs during a manual decompression schedule, the program output will note it with the comment "BENT" at the stage at which it occurs. This indicates that the decompression model itself was violated. While according to the program output it is possible to recover from such a situation at subsequent points in a multilevel dive, the reality is not so rosy, and "BENT" at any stage of a dive should be considered BENT for good. A good example of this is that a suitable surface interval will mathematically clear a BENT indication in the program, but obviously not in real life !

If conservatism factors are being employed with a manual decompression schedule and they are violated, the program output will note this as "VIOL". This is not the same as BENT, you are still within the bounds of the decompression model. Unlike a BENT, it is possible to realistically recover from a VIOL.

To go on 100% O2 at 20 feet, push the Max PO2 up to 1.61. Owing to the stepped nature of decompression schedules, this is unlikely to affect any other deco stop/mix combination. You will, however, notice a resultant jump in the CNS figures from the extraordinary exposure. ( The CNS exposure tables are extrapolated a small ways in both directions to account for extraordinary exposures. )

Ascent / Descent Rates

You may specify Ascent and Descent Rates for both deep and shallow segments of a dive, along with a "split" depth in feet. Rates may be set between 10 and 100 feet per minute; no negative numbers. Un-checking the boxes disables Ascent / Descent modeling. This is not a good idea, but is sometimes useful for comparing with old square-profile schedules and softwares.

Miscellaneous Controls / Error / Reset Buttons & Password

When you have set up all your input parameters, click the ERROR button to generate results. The Reset button resets the interface to default values, including replacing the waypoint information with the example, so save your waypoints elsewhere before using Reset. The unlabeled field next to the buttons is for the program Password.

Debug pollutes the screen with on-the-fly intermediate calculations before displaying the regular program output.

M-values will print out a listing of the M-Values for the selected model, with no deco analysis.

Print Headers Last is self-evident - it inverts the order of program output, so that the most interesting parts come first.

Pressure Graphics causes lovely ASCII-art tissue compartment loading graphs to be drawn before the regular program output. Actually, the graphs are quite interesting and instructive. Below are some examples:

During decompression, the ambient pressure line follows the decompression ceiling back to the surface line. The decompression ceiling is drawn towards the surface line by the inert gas line. When the decompression ceiling is entirely to the left of the surface line, decompression is complete. Conversely, for no-decompression models, the decompression ceiling is fixed, and becomes the no-decompression limit. The PO2 line has no effect, and is just shown for interest. Studying complete sequences of these graphs for various decompression schedules can greatly enhance your intuitive understanding of the decompression process.

References

• An Explanation of Professor AA Buehlmann's ZH-L16 Algorithm - Paul Chapman
• DIY Decompression - Stuart Morrison
• Introductory Lessons About Dissolved Gas Decompression Modeling - Erik Baker
• Clearing Up the Confusion About "Deep Stops" - Erik Baker
• Understanding M-Values - Erik Baker
• Oxygen Toxicity Calculations - Erik Baker
• Calculating No-Stop Time - Erik Baker
• Gas Exchange, Partial-Pressure Gradients, and the Oxygen Window - Johnny Brian
• Tolerating Exposure to High Oxygen Levels - Bill Hamilton
• Pressure Conversions
• DeepOcean.net