No safety stop during dives

[ianr33]

IMHO splitting dives up into different categories (Safety Stop optional,Safety Stop required, Mandatory Deco ) is kind of missing the point.

When we learn tables and later when we start using a dive computer deco is always considered to be black/white . Either you are doing a recreational dive (No deco) or you have gone beyond the tables (deco).
In reality there is no sharp dividing line. More like a very,very wide gray area. Dive computers reinforce this misconception. Saying you are one minute away from deco is pretty meaningless.

Most tables give the NDL for a single dive to 100 feet to be 20 minutes.If I did that after a night of hard drinking and during the dive did a couple of rapid ascents to,say,40 feet then I would not be at all surprised if I got bent.

On the other hand I could dive to 100 feet for 30 minutes.Do a slow ascent,deep stops ,good safety stop and expect to be fine most of the time (I'm not sure if most here means 99% or 99.9999% of the time)

Bottom line is that of you have been to 20 feet for 20 minutes then you dont need a stop. If you have been anywhere near/beyond the tables then the longer the safety stop the better.

There is NO WAY I would choose to do a dive to 130 feet followed by a direct ascent to 10 feet for a 3 minute safety stop although its allowed by the tables.

[navyhmc]

Another reason to take a safety stop: Another 3 minutes of dive time!

Ianr33: I totally agree with your 130' statement. 1. slow ascent. 2. deep stops: 75' and 45' both for 2 min with a SS at 15' for 3.

In fact, in my log, I have a deep stop table for rec dives to 130', all include a 15' safety stop:

130': 75' and 45'
120': 70' and 40'
110': 65' and 40'
100': 60' and 35'
*90': 55' and 35'
*80': 45'
*70': 40'
*60': 35'

* only if w/i three letter groups of NDL's on tables. No deep stops needed less than 50'

To me, the deep stops become even more important on repetative dives and I will usually do them for any dive over 50' if it's not the first dive.

[ianr33]

navy, how did you decide on the depth for the first deep stop? To me they seem a bit too deep.
If you play with a 130 foot dive on V-planner such that its around the NDL "limit" then offgassing starts around 70 feet. Being deeper than that will only increase your nitrogen loading.

<< DIVE PLAN
Surface interval = 1 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 2

Dec to 130ft (2) Nitrox 28 60ft/min descent.
Level 130ft 12:50 (15) Nitrox 28 1.38 ppO2, 116ft ead
Asc to 30ft (18) Nitrox 28 -30ft/min ascent.
Stop at 30ft 0:40 (19) Nitrox 28 0.53 ppO2, 24ft ead
Stop at 20ft 2:00 (21) Nitrox 28 0.45 ppO2, 15ft ead
Stop at 10ft 4:00 (25) Nitrox 28 0.36 ppO2, 6ft ead
Surface (25) Nitrox 28 -30ft/min ascent.

Off gassing starts at 72.3ft >>

On a 130 foot dive around NDL I would probably pause at 70 feet (for maybe 10 seconds) then ascend at around 10 feet/minute to 30 feet where I would play around until I got bored.

To a large extent though this is splitting hairs. Just about anything is better than heading straight up to 10 feet.

This is an excellent article for anyone interested in this stuff. Decompression myths and mistakes Although it is aimed at deco dives the principles still apply.

[navyhmc]

Going off the Pyle stop formula: 1/2 the distance between the planned depth and the first stop-in this case being the 15' safety stop. For the 130', this is actually 72.5 feet so I elected to round it up to 75'. Rounding down to 70' would also work. I hadn't done a v-planner on this though.

My Caveat though is that even at 75', I've noted my Nitrogen loading on the computer drops sometimes while I'm at 75' for 2 minutes. Understandibly, even more so at 45'.

[ianr33]

That makes sense but I'm guessing that "planned stops" really refers to Deco Stops (likely from a Buhlman Algorithm) In which case on an NDL dive your planned stop is the surface and the Pyle stop would be at 65 feet.

As I said though,this is measuring with a micrometer and cutting with an axe !

[navyhmc]

Well, you're question has made me think it over a little, I may need to "round shallow" rather than deep when it comes to off gassing.

I will admit that the deep stops I take are from the thoughts of a guy who does very deep dives in the 200'-300' range, but stacking the odds in my favor never hurts.

[Splitlip]

I'm gettin' a Haddock,

[in_cavediver]

Originally Posted by navyhmc

Well, you're question has made me think it over a little, I may need to "round shallow" rather than deep when it comes to off gassing.

I will admit that the deep stops I take are from the thoughts of a guy who does very deep dives in the 200'-300' range, but stacking the odds in my favor never hurts.

Personally, I wouldn't sweat it. The realized difference on a dive between 70 and 75 is very small. First, factor in gauge accuracy and that is usually ±2ft or so. Then, factor is physiology which is quite random from person to person. 65-75 is a good stop point. The model may or may not say you are off gassing but the question is does it work for you and your body?