Reviewing concepts

• Gas absorption and eliminations by a giving tissue happens exponentially. Some models like the VVAL 18 work with lineal outgas.
• DCS is caused by the formations of bubbles, quantities, and sizes.
• Gas tension in a tissue must not exceed about twice the ambient pressure, although today it is known that different limits exist for different tissues.
• Activation of the complement system is a large contributor factor.
• “SAFE” implies no risk and, when we discuss tables, algorithms, or deco- procedures there is always a probability of DCS no matter how small, even when diving within the limits established.

Individual susceptibility to DCS, environment and other factors influences the risk of DCS.

• Dehydration
• Age
• Carbon dioxide
• Cold
• Exercise
• Injuries
• Patent foramen ovale
• Fitness
• Rapid Ascent, Etc.

Other factors that have a major influence on decompression is the ability to determine proper deco, to maintain the deco stops and the ability to response any emergency.

Before continuing to the example, look at the other posts for review

Evolving thinking

Ratio 1:1

• Depth Range 24m (80′)- 51m(170′)
• Bottom time: 10 min to 120 min
• Gases: Air; 32; 25/25; 21/35 or 18/45
• Deco gases need it: 1 with Nitrox 50%
• Set Point: 45m(150′)

Example:

Dive to 45 meters with 21/35 deco gas Nitrox 50 for 30 minutes bottom time.

Table

Depth- meters	Ratio- Minutes
24	-35 min.
27	-30 min.
30	-25 min.
33	-20 min.
36	-15 min.
39	-10 min.
42	-5 min.
45	1:1 set point
48	+5

Set point refers to every minute of bottom time you spend you will need to do a minute of deco.

In our example you need to do 30 minutes of deco. The first question to ask is- where to do the first stop? Normally you should do the first stop above the off gassing zone and, following the current procedure it will start around 75% of the depth which is 33 meters.

Remember that the first stop depth is related directly to the pressure change from the maximum dive depth and, we know that first stop location is primarily to limit and prevent bubbling quantities and sizes from growing large early in the ascent.

Other way to calculate the deco-zone is depth- 2 ata, which is 45m- 10 m (2 ata) = 35 m. It’s possible to Calculate this accurately using bubble mechanics, the exact deco-zone start at 30 meters; thus, our first stop must be above that depth.

As the diver is going to change gases at 21 m; to maximize the oxygen window, is better to do the first stop at this point. The deco- zone concept is important, because if we do our first stop at more depth than that the diver will be on-gassing.

As described above, if the diver is between 0 min and 59 min of deco, the first stop is always at 21m. If the diver is out of this range of deco, for example UTD apply the following set of rules:

Depth	0-59 minutes	60- 89 minutes
50 % deep stops	1 minute	2 minutes
60% deep stops		1 minute

The ascent time up to 21 meters is determined by the velocity ascent of 9 m/min plus 1 minute, rounded.

Now divide the deco in 2 parts. So, 15 minutes will be spent between 21 meters up to 9 meters. Then you will shape the curve between 5 stops: 21, 18, 15, 12 and 9 meters.

Approach A:

The procedure is to divide 15 minutes into 5 stops. To calculate the deep stop portion of time, dividing 15 minutes by 5 stops is equal to 3 minutes. Thus 3 minutes should be enough for the gas switch. Then you want to spend the least amount of time up until you reach 9 meters, hence at 18 m, 15 m and 12 m you will stay 2 minutes each and, the rest, 6 minutes at 9 meters for a total of 15 minutes.

Approach- S curve:

• 15 min ÷ 5 stops = 3 minutes per stop
• Keep the bottom two stop times the same, halve the two shallower stops
rounding up, and the rest at 9m stop.

Depth	Initial time	S curve	Approach A
21	3 minutes	3 minutes	3 minutes
18	3 minutes	3 minutes	2 minutes
15	3 minutes	2 minutes	2 minutes
12	3 minutes	2 minutes	2 minutes
9	3 minutes	5 minutes	6 minutes
5 stops	15 minutes	15 minutes	15 minutes

Shaping the Shallow stops

The remaining 15 minutes will be weight toward 6 m and 3 m stops.

Depth	S curve	Approach A
6 meters	15 minutes	5 minutes (33%)
3 meters	1 min/meter ascent to the surface	10 minutes (66%) + 1 min/meter ascent to the surface

Running the tables on VPM

Depth	Stop	Run	Mix
45	–	2	21/35
45	27	30	21/35
24	–	32	21/35
24	0:40	33	21/35
21	3:00	36	50
12	–	40	50
12	3:20	40	50
9	4:00	44	50
6	6:00	50	50
3	12:00	62	50

Running the table on Cochran EMC-20H

Depth	Stop	Run	Mix
45		2	21/35
45	28	30	21/35
24	0:21	31:31	21/35
21	1:36	33:17	50
18	1:30	34:57	50
15	1:21	36:38	50
12	2:14	39:12	50
9	3:57	43:29	50
6	5:42	49:31	50
3	7:16	57:07	50

I hope you found this information useful but by no means use these examples for diving. Look for proper training in a recognized diving agency. This post is only for educational purposes.

Planning the dive in the field with DiveSoft DC