- Basics on Decompression Diving
- Table Handling
- Computer Handling
- Inertgasbubbles
- Ascent Pattern (© ALBI)
- a very special Table
- the United States Navy Table, Air, Revision 6 (04/2008)
- a little "examplay"

back to: DIVE TABLES homepage

As well you learned the usage of Standard-Air Tables (RDP, US Navy Table, ... ) and how a dive computer can support you. As well you learned something about the maximum ascent speed and how to conduct a safety stop.

Thus in contrast to a decompression dive. This dive is ended with stops in certain depths for a definitive time.

Technically speaking: "Every Dive is a Decompression Dive!"

Why? An ascent means just a reduction in the ambient pressure: this per-se, is: **De-**compression,
and as such valid for all these dives.

The difference is just the ascent procedure!

First of all, a couple of examples of No-Decompression-Limits (NDLs) and the maximum ascent speed:

**PADI RDP:**

18 m: 56 min,

40 m: 9 min,

max. ascent speed: 18 m/min (= ca. 60 ft/min = 1 foot / sec!)**NAUI:**

18 m: 55 min,

39 m: 8 min,

max. ascent speed: 9 m/min (= 1 foot/2 sec)**SSI:**

18 m: 50 min,

39 m: 5 min,

max. ascent speed: 10 m/min**USN, Version 1983:**

18,2 m: 60 min,

39,6 m: 10 min,

max. ascent speed: 18 m/min (former)

since 1993: 10m/min (30 ft/min)**DCIEM:**

18 m: 50 min,

39 m: 8 min,

max. ascent speed: 18 + - 3 m/min**DECO 2000:**

18 m: 45 min,

39 m: 9 min,

max. ascent speed: 10 m/min

Nice to know:

the value of 1 ft/sec developped historically as the arithmetically mean
of the ascent speed of hard hat divers with that from combat divers: it should be uniform
in all the navies manuals. So there is no unalterable physical law behind it.

As well the NDLs are subject to change in the course of time and differing
by as much 20 to 25 %. So here as well there is no absolute truth behind it; instead
a lot of statistics and ball-parks about human physiology.

The whole story becomes thrilling very quickly by operating repetitive dives!

We need the repetitive, or pressure group (PG ) and the length of the surface intervall (SI).

The paradigm is SI = 60 min, the results the adjusted NDLs for this 2nd dive to be also

a No-Deco dive.

**PADI RDP:**

18 m: 56 min,

PG: W , after SI -> I

now adjusted NDL at 18 m: 30 min**NAUI:**

18 m: 55 min,

PG: I , after SI -> G

now adjusted NDL at 18 m: 11 min**SSI:**

18 m: 50 min,

PG: H , after SI -> G

now adjusted NDL at 18 m: 6 min**USN, Version 1983:**

18,2 m: 60 min,

PG: J , after SI -> H

now adjusted NDL at 18 m: 8 min**USN, 2008:**

60 ft: 60 min,

PG: K , after SI -> J

now NDL at 60 ft: 2 min**DCIEM:**

18 m: 50 min,

PG: F , after SI -> RF = 1,6

now adjusted NDL at 18 m: 30 min**DECO 2000:**

18 m: 45 min,

PG: F , after SI -> C

now adjusted NDL at 18 m: 6 min

Now the variation in the adjusted NDLs can be up to 500 % !!!

And so does the safety?

You look up the DECO 2000 table from Dr. Max Hahn. (This table is in widespread use all over europe, it comes for: AIR, Nitrox32, Nitrox36, at sealevel and as well the whole bunch for mountain-lake diving!)

You round up and you will find the following entry under 39 m and 18 min:

6 m / 3 min, 3 m / 7 min, F

This means very simply you have to stay in 6 m depth for 3 min,

and as well in 3 m depth for an extra 7 min.

So your effective dive time (not your bottom time) has increased about 10 min.

Therefore you will need extra air.

The letter "F" simply designates your **Pressure Group (PG)**
and is a coarse measure of a calculated (assumed) inertgas load in the body,

resp. in a so-called "compartment" (a mathematical model with a designated halftime in minutes for a piece of body tissues).

As well with these halftimes there is no flying magic: halftimes are basically just

the reciprocal of the blood perfusion in this model-tissue.

For the **plan** beeing on the safe side concerning air consumption and cold / exertion,

you look up the next greater depth or the next greater time or **both**.

i.e.: 39 m and 21 min or:

42 m and 19 min. This gives you: 9 m / 2 min, 6 m / 4 min, 3 m / 10 min.

The actual dive profile now looks like that:

after 18 m at 39 m you go up slowly to 9 m and stay there 2 min, then slowly to 6 m,

after 4 min you are allowd to rise to 3 m for additional 10 min.

For these additional 16 min of time spent under water you need approx. 800 liters.

(16 * 2 * 25, that is with an Surface-Air-Consumption (SAC) rate of approx. 25 l / min plus a little bit reserve.

So with a 12 l bottle you could hit empty ... How to avoid?

Now we check again the PG:

- 39 m / 18 min gives: F, total time-to surface (TTS) approx. 14 min
- 39 m / 21 min: F, TTS approx. 19 min
- 42 m / 19 min: F, TTS approx. 20 min

We see: this pattern is relatively coarse. Why so?

And: what's the story with cold water and the next greater time/depth?

Well, there is the funny **Henry's Law**
and a change in the **blood perfusion** of your skin and muscles.

Surely enough, having another table or dive computer will yield other figures? Why this?

Now let us check a couple of these other tables:

In the rough data with 39 m / 18 min we will get:

- merciless: the good old
**BSAC**(British Sub-Aqua Club) Table gives at 39 m / 20 min: 6 m / 1 min - workhorse
**U.S.N.**(United States Navy) Table after all (39,6 m / 20 min): 3 m / 4 min **IANTD**Table (in [46], S. 233) at 39 m / 20 min: 9 m / 1 min; 6 m / 2 min; 3 m / 11 min- IANTD
**accelerated deco**, with minimum EAN75: 6 m / 1 min; 4,5 m / 7 min **DCIEM**Table (39 m / 20 min): 6 m / 8 min ; 3 m / 10 min

(Rem.: DCIEM = Defence and Civil Institute of Environmental Medicine, in Canada)- the
**USN, 2008**gives us at 130 ft / 20 min: 4 min stop at 20 ft (Air), **or: 2 min stop at 20 ft with O**_{2}!

As well there are various mindsets on how to deal with cold and exertion,

and, these mindsets are subjected to change in the course of time due to
different approaches to the so-called "critical super-saturation".

Here a couple of examples, (the [No. #] is the reference in my
Literature List):

- only next greater time ([43], p. 28 resp.
**NOAA**[48], p. 4-30),

(NOAA = National Oceanic and Atmospheric Administration, U.S. Department of Commerce) - to increase the safety stop with additional 3 min
- next greater depth resp. +10 feet (PADI)
- next greater time plus next greater depth (USN from [29], p. 210)
- DCIEM Table [28]:
**without any**surcharges!

How came? Well, very easy: this table is designed form the first for canadian waters (damn cold) and a well-defined exertion!

In order to get along, you should know all the displays of your computer by heart!

Normally you see the actual depth (DEPTH 39 m) and dive time (BOTTOM 17 min),

as well the calculated TTS, and where and how long the deepest deco stop is.

(Rem.: DEC = Decompression, P is the oxygen partial pressure, ASCENT displays the ascent speed)

Here we see the Ceiling at 12 m: so you ascent slowly to approx. 12 m, then starting your stop procedure!

Here we see the display during the ascent from the 6m stop to the next, the 3 m stop.

The remaining stop time being 7 min, the dive time increased already to 26 min.

Other computers may give additionally **deep stop** information:

so, for this dive with another computer we will have:

22 m/2 min, 14 m/1 min, 6m/1 min, 4.5m/10 min

More interesting question:

- What will happen if (provided your are diving with a table) you inter- or extrapolate (i.e you botch your rectangular profile!), according to the motto: uuhpps, I wasn't that deep, but so and so long ...
- How can NITROX help?
- Enter Helium: what does it change?
- What happens with the fast and the slow compartments during a safety stop?
- What the hack is a "DEEP STOP" ?
- How do I make an " accelerated deco "?
- What the hell is Sur-D (surface decompression)?
- Why should you very strictly check the hydration of your body?
- And what are the changes through the new USN Table from 2008 ???
- New Doppler-Ultrasonic measurements see a lot of bubbles, even with No-Deco dives!

Will the notion "NDL" vanish from the traditional diving education? - A widespread opinion (ill-believe): I am 100% protected if I am useing tables/computers
correctly! Well, the facts are really different!

Why so? And what can we do to correct this situation?

To a certain degree the body can handle this and a lot of bubbles get stuck in the lung-filter and are down-breathed with no signs or symptoms. But if there are too much bubbles or they get too big then we are on the verge of decompression sickness (DCS).

The amount of bubbles and the bubble volume is mainly dependant on: dive depth, dive duration and ascent speed.

Dive Tables resp. Dive Computers should assist us to dive such profiles that DCS can be avoided.

Normally this is the rationale for No-Deco Dives.

As was indicated above, there are measurements, showing a lot of inert gas bubbles even for dives within the NDLs! Here we see the plot for a No-Deco-Dive (30 m, 20 min) in comparison with the same dives, but with safety stops:

Doing a safety stop reduces the bubbles, but the bubble reduction is even more
pronounced with an **additional deep stop at 6m**

As well quite nice to know: the ideas of the "**deep** stops" has been published already in 1908 by Haldane.
However, it went to historical oblivion, but a strict scientific reason has been proved already in the 60's by Hills, B.A.

in an investigation of 163,400 No-Stop-Dives according to the USN, Version 1983 table between 21 and 55 feet there have been 48 DCS incidents ...

This is exactly why a lot of diving pro's prefer the following **ascent pattern**, especially with long "No-Deco-Dives":

**12 m / 1 min, 9 m / 1 - 2 min, 6 m / 4 min, 3 m / 2 min.**

So any time your dive computer tells you to go straight to the surface:

slow down, young feller ... If your DC shows up some deco time already, you just add this deco time to the ascent pattern.

Interestingly enough, this resembles more or less the paradigm, developped 2001 by the DSL.

The DSL is the **Diving Safety Laboratoy from DAN/Uwatec**.

These tables have been provided by my late friend, **Dr. Max Hahn in 1992** for a UHMS meeting:

here just 2 short parts for 39 and 42 m:

As well this table meets the requirements of the DSL - PMRC concept from 2001:
**PMRC**: Proportional M-Value Reduction Concept.

The unacceptable number of DCS incidents for longer and / or deeper dives had to be reduced. Starting point was the extensive research of Dr. Edward D. Thalmann, Captain, Medical Corps, U.S.Navy (now retired) and as well from Edward Flynn and Wayne Gerth.

This culminated in various sets of modified M-values, which have been tested in thousands of controlled dives in the NEDU chambers.

The system with the less DCS hits was the one which was called after the name of the FORTRAN source code variable: VVAL18.

What are, in brief, the highlites of the new
**Air Table from 04/2008, Revision 6**?

- no metric values
- from 10 to 60 fsw depth increment in 5 ft
- the NDLs begin at 25 fsw (7,6 m)
- here and there reduced NDLs
- normally just one PG up
- here and there increased stop times
- the SI end after 12 h only up to PG K
- i.e.: with PG L after 12:12, PG O after 14:58, and for PG Z only after 15:50!
- the 10 feet stop was completely moved to 20 feet:
- there are no longer any 10 feet stops!
- 2 decompression modi in water: Air, Air/O
_{2}, - 1 Surface Decompression Modus (Sur-DO
_{2}): O_{2} - 5 min air breaks for every 30 min of O
_{2}breathing - there are hints for the deco modus to be applied and the # of airbreaks
- for under water ship husbandry:
- an optional shallow water air table from 30 to 50 fsw in 1 ft increments

And here is my "test"-dive: 42 m

We are planning 3 dives:

18 m / 45 min, 1 h SI, 18 m / 25 min, 1 h SI, 18 m / 25 min:

here "effective" means really in effect for the table.

**PADI RDP:**

18 m: 45 min,

PG: R , after SI -> F

now adjusted NDL at 18 m: 36 min**1. st Repetitive Dive:**

18 m: 25 min,

residual nitrogen time: 20, effective bottomtime: 20 + 25 = 45 min

18 m: 46 min ->**PG: R, an easy No-Deco Dive**

after SI -> F**2. nd Repetitive Dive:**

18 m: 25 min,

residual nitrogen time: 20, effective bottomtime: 20 + 25 = 45 min

18 m: 46 min ->**PG: R, as well a No-Deco Dive****DECO 2000:**

18 m: 45 min,

PG: F , after SI -> C

now adjusted NDL at 18 m: 6 min**1. st Repetitive Dive:**

18 m: 25 min,

residual nitrogen time: 39, effective bottomtime: 39 + 25 = 64 min

18 m: 65 min ->**Deco Stop 3m / 8 min!**

after SI: residual nitrogen time: 43, adjusted NDL at 18 m: 2 min**2. nd Repetitive Dive:**

18 m: 25 min,

residual nitrogen time: 43, effective bottom time: 43 + 25 = 68 min

18 m: 75 min ->**Deco Stop 3m / 14 min!****DCIEM:**

Rem.: RF = repetitive Factor

18 m: 45 min,

18 m, 50 min, PG: F , after SI -> RF = 1,6

now adjusted NDL at 18 m: 30 min**1. st Repetitive Dive:**

18 m: 25 min,

effective bottomtime: 1,6 * 25 = 40 min

18 m: 40 min ->**PG E, due to the 3rd dive: adjustment of PG to G, RF = 1,7**

after SI: adjusted NDL at 18 m: 30 min**2. nd Repetitive Dive:**

18 m: 25 min,

effective bottom time: 1,7 * 25 = 42,5 min

18 m: 50 min ->**No Deco Stop!****USN, Version 1983:**

18 m: 45 min,

18.2 m, 50 min PG: H , after SI -> G

now adjusted NDL at 18 m: 16 min**1. st Repetitive Dive:**

18 m: 25 min,

residual nitrogen time: 44, effective bottomtime: 44 + 25 = 69 min

18 m: 70 min ->**Deco Stop 3m / 2 min!**

after SI: residual nitrogen time: 61, no adjusted NDL at 18 m possible**2. nd Repetitive Dive:**

18 m: 25 min,

residual nitrogen time: 61, effective bottom time: 61 + 25 = 86 min

18 m: 100 min ->**Deco Stop 3m / 14 min!****USN, 2008:**

60 ft: 45 min, PG: H , after SI -> G

now NDL on 60 ft: 20 min

RNT: 40 min**1. st Repetitive Dive:**

60 ft: 25 min,

RNT: 40, EBT: 40 + 25 = 65 min

yields 60 ft: 65 min ->**Deco Stop 20 ft / 2 min! (or:**

Deco Stop 20 ft / 1 min with O_{2}

RNT after SI: 65, no NDL**2. nd Repetitive Dive:**

60 ft: 25 min,

RNT: 65, EBT: 65 + 25 = 90 min

yields 60 ft: 90 min ->**Deco Stop 20 ft / 23 min! (or:**

Deco Stop 20 ft / 10 min with O_{2}

Well, now you can see very quickly:

An all-is-easy happy bubbles No-Deco-Dive without any even recommended-only safety stops within one educational framework

could be simply forbidden / not possible within another framework or,

can imply within the next framework a dive with real serious decompression obligations!

Or, there can be a deco stop of considerable length with even O_{2} breathing!

The easy and very clear take-home-message here is:

the sharp separation between No-Deco and Deco dives, which certain educational frameworks are juggling with,

is not that sharp ....

back to: DIVE TABLES homepage