Diving with gradient factors for a new recreational diver

[boulderjohn]

This might have come about pre-common-computers when many were using tables for air or 32%; setting anything in-between required the complication of EAD tables and nobody did it.

You are probably right. It's a good example of a phenomenon that occurs in almost all activities--a practice that made sense originally carries on even though changing circumstances mean it no longer makes sense.

 

[inquis]

The DSAT algorithm targets recreational repetitive diving and has been tested with much success. Such profiles are widely regarded as safe to ascend WITHOUT a safety stop (under a pretty reasonable ascent speed assumption). A high gradient factor of 95 yields NDL times that are fairly comparable to DSAT. There are many ways to reduce risk without going against the grain:

• A safety stop (likely required by most commercial operators unless emergency)
• Dropping the GF to 85 or 75
• Starting ascent before NDL expires
• Diving nitrox may shift the limiting factor to remaining air (thus you would have more NDL time remaining when starting your ascent).
• Slow ascents during the last 5-6 meters. (DSAT now uses 10 m per minute, so perhaps target 5 m or 3 m per minute.)

Enjoy your diving!

 

[tursiops]

The DSAT algorithm targets recreational repetitive diving and has been tested with much success. Such profiles are widely regarded as safe to ascend WITHOUT a safety stop (under a pretty reasonable ascent speed assumption). A high gradient factor of 95 yields NDL times that are fairly comparable to DSAT. There are many ways to reduce risk without going against the grain:

• A safety stop (likely required by most commercial operators unless emergency)
• Dropping the GF to 85 or 75
• Starting ascent before NDL expires
• Diving nitrox may shift the limiting factor to remaining air (thus you would have more NDL time remaining when starting your ascent).
• Slow ascents during the last 5-6 meters. (DSAT now uses 10 m per minute, so perhaps target 5 m or 3 m per minute.)

Enjoy your diving!

The DSAT algorithm is what the PADI RDP is based on, which DOES require safety stops for certain dives, and that is a best practice even if your computer says otherwise.

 

[inquis]

The DSAT algorithm is what the PADI RDP is based on, which DOES require safety stops for certain dives

Thanks for that correction.

 

[rjack321]

After about 30 dives I've fallen in love with diving and want to pursue the hobby more actively. Unfortunately, I'm a worrying personality, risk averse, and despite being a decent swimmer and a triathlete, I'm not a natural when it comes to diving and buoyancy control. I want to find ways to enjoy the sport more safely, especially as it relates to DCS risk.

DAN vignettes, ScubaBoard (especially advanced scuba), and talks like Pollock's and Marroni's have been invaluable in my safety pursuit. Most recommendations are fairly straightforward and applicable on all/most dives. As I read through the forums and research articles, however, I come to the conclusion that using conservative gradient factors with multiple stops instead of the popular 3 minute safety stop at 5m (15ft) is a good idea for minimizing risk. But is it practical to do, especially for an inexperienced diver without a regular dive buddy?

So here we go:
Do the safety benefits of multiple safety or deco stops (and diving with conservative gradient factors) outweigh the awkwardness and inconvenience of having to do them on recreational dives? Is it practical?

The pros:

1. safety - deeper than 5m stops seem to reduce bubble and DCS risk in recreational dives (somewhat significantly).
   FWIW, I don't want the discussion to get mired in whether deep stops are good or bad, but my reading of the journals is that while "too deep" is not good, some deeper than 5m stops are good for reducing bubbling in recreational divers. FWIW, for most recreational dives these seem to be at the deepest in the 12 to 9 meter (40-30ft) range depending on the dive profile and gradient factors chosen.

The cons:

1. Different (i.e. more conservative) safety / decompression protocol that (almost) everyone else in a real life recreational dive group
   1. stops different that the 5m / 3 min safety stop - both deeper and shallower stops
   2. longer total stops time
   3. (with conservative factors) high likelihood of decompression time while everyone else is in NDL
   4. (with conservative factors) lack of clarity how to handle emergencies while having deco time while others are in NDL
2. Having to convince the group to follow a different more conservative protocol - not very likely or practical
3. Separating from the group by a few meters for a stop - I guess this is an outright bad idea for a new diver, a diver without a regular buddy, might be against the manual, and I don't expect it would be tolerated by many dive masters
4. A more expensive dive computer
5. Complexity

What do you kind and knowledgeable folks recommend for someone in my situation? Is it a bad idea for a newbie diver to try to dive with multiple stops and conservative gradient factors?

With all these plans and modifications....

Do you even know how to calculate how much gas this will take to actually implement? The number one cause of death and injury in new divers is not DCS, it's running out of gas.

PS I think you are way overthinking this. GF-low doesn't even apply to recreational no stop diving. Turn up the conservatism on your computer, do 5 to 8 minutes shallow instead of a 3 min safety stop. Skip the unproven "deep" recreational stops. And try to enjoy the fish

 

[inquis]

Regarding the slowing of your ascent, I don't think a lot of divers appreciate the magnitude of this adjustment. For instance, if we take the commonly recommended limit of 10 m per minute, that is a relative pressure change of 33% per minute at the maximum recommended depth for newly certified divers (20 m). It's also VERY illustrative to examine the time required per meter of ascent (denoted as "period" below). To maintain that same relative pressure change, the ascent speed must slow and period must increase, giving the following (period rounded to nearest second/m):

Depth (meters)	Ascent Rate (meters per minute)	Ascent Period (seconds per meter)
40	17	4
30	13	4
20 (reference)	10 (reference)	6 (reference)
15	8	7
10	7	9
6	5	11
3	4.3	14
1	3.7	16

The OP seemed to prefer metric, but here are the numbers for imperial (ft/min and seconds per foot, rounded to nearest 1/2 second/ft) for a reference of 30 ft/min at 60 ft depth (a relative pressure change of 32%/min, so slightly less than the metric table):

Depth (feet)	Ascent Rate (feet per minute)	Ascent Period (seconds per foot)
130	53	1
100	43	1.5
60 (reference)	30 (reference)	2 (reference)
40	24	2.5
30	20	3
15	15	4
5	12	5
1	11	5.5

 

[inquis]

As an aside, if you shoot a DSMB with a spool, the imperial period is quite useful, since you can easily reach a foot further along the line and wind it up, but also ensure that you wait long enough before reaching for the next foot of line. This makes for a VERY controlled ascent, especially if you use a flat value of, say, 6 seconds per foot after your safety stop.

 

[Wibble]

There's so much to learn in the early days of scuba. Then there's a lot more to learn in the later stages of scuba. It gets harder from there!

It really is best to concentrate on certain aspects of diving and really, really get them sorted. There's a bunch of core skills -- buoyancy, trim and finning -- which, when mastered, make life so much better underwater.

There's a progression as you move through the 'grades'. There are good reasons for this which often doesn't seem to be apparent when starting out.

Take deeper diving for example. You hardly feel any difference between 30ft/10m and 300ft/90m, but the main difference is that at 300ft/90m there's so many things that can go wrong and it can very easily kill you if you haven't mastered the planning, huge amounts of specialist equipment including many different gasses, specialist techniques not to mention all the fall-back practice for when things go wrong as they surely will at that depth.

But back up at recreational levels, a dive to recreational limits 40m/130ft has so many gotchas too. You've got to be competent with your skills to control that dive and safely execute it. You've very little time at depth, 9 minutes at the bottom (PADI RDP); you'll be massively going through the gas in your single cylinder; know how you handle narcosis; you need to have sufficient for your ascent; sufficient in reserve; you must be able to do your decompression safety stop without holding on to ropes; look after other people "in your team"; not be phased by putting up SMBs; the list goes on and on.



What I've learned... I was so eager in the beginning to do deeper, longer dives. Looking back now feel I genuinely embarrassed at my early-days skills. I now know that one doesn't know what one doesn't know. I now know that I now understand what people meant when they said to me that I should slow down and learn to walk before running.

Diving's not a sprint. It really is a lot more fun when you've mastered certain skills and can move on to the next ones.


For what it's worth, I'm dedicating this year to having a year of skills consolidation. I've no intention to do any other courses, although I may well pay for some mentoring days to fix some of my weaknesses (teamwork from too much solo diving!). I want to know that I can properly do all the diving I'm qualified to do... and to execute them as effectively as possible. Everything's so much easier thereafter!

 

[Angelo Farina]

Deco stops are by definition technical diving and should not be done without proper understanding and training.

This concept that deco is "technical" is typical of American for-profit training agencies. Here in Europe we mostly have non-profit training bodies, such as CMAS, BSAC, FIPSAS or the like. All these allow for deco stops for recreational divers, and consider that below 30 meters the safe and correct way of performing a recreational dive is with planned deco. Of course divers are properly instructed and trained (and equipped) for deco stops on this side of the pond. Usually some amount of deco training is given already in the first course.

 

[inquis]

Conceptually, though, a deco dive is more technical (both to plan and execute) than just swimming around until 700 psi and come up. My feeling is the latter is the vast majority of recreational divers in the US. Not criticizing them, they simply don't have to make more detailed (aka "technical") calculations or decisions to remain safe.

If a line is to be drawn, deco (or other overhead restriction) seems like a reasonable boundary. That just means your instruction extends into the technical realm a bit. I personally think that's a good thing, but I am also more technically inclined!