Computer recommendations for New Divers

[Angelo Farina]

It's questionable: you could argue that DSAT's level of "liberal" is proven to be safe enough, and any DCS hit at DSAT's level of "liberalism" would already be classified as "undeserved". It would be attributed to PFO or bad hangover or some other thing that is not accounted for by the computer. So the question is, if it's not accounted for in the first place, will any additional conservatism compensate for it enough? Or at all? And if the condition does not exist in a particular diver, does added conservatism make any practical difference to that diver's risk?

Sorry, by my engineering studies here need to kick in. Safety is the result of following the rules, and then taking some "SAFETY MARGIN". The larger this margin, the greater the safety.
If you think to be safe just staying in the edge of the rule, there will be high chances that something goes worse than expected, and you will be hit.
So for me the extra safety margin provided by a conservative computer is something highly valuable.
In this case getting extra safety does not need an additional cost, as actually these computers are the cheapest on the market... So I really do not see the point of spending more for being less safe.
I appreciate instead spending more for a larger, colourful display, very easy to read, and for practical features such as the capability of transmitting your diving profile over Bluetooth instead of needing a special cable, or to be able to change the battery yourself without any special tools.
Then there is tech diving, but that is entirely another world... Where "safety" is not anymore your priority, being replaced by a "risk management policy", which is something quite different.

 

[scubadada]

If you would like to see the probability of DCS based on depth and bottom time, you might be interested in the SAUL Recreational Dive Planner SAUL Recreational Dive Planner | Modern Decompression The bottom line, the longer the bottom time, the greater the risk for DCS. So, in some ways, @Angelo Farina is correct, but the difference may be between two very low probabilities, so, @dmaziuk can be correct also

 

[Gary_Ward]

And if the condition does not exist in a particular diver, does added conservatism make any practical difference to that diver's risk?

But if we follow that argument to its next natural conclusion, then you get to why have any conservatism modes on any computers? The reality is that the models used and how conservative they are is based on a number of factors. Choice being one of them (people can choose to adjust their settings, or not. They can also choose the brand of computer which is also conservative (Cressi, Oceanic etc), or not). The second has clearly got to be a degree of arse covering too. No one wants to be the manufacturer of a computer with the reputation for bending divers. I don't have a problem with having new divers, who might breathe through their air like a steam train, diving with a computer which is more conservative than mine, as they're probably going to inturn a lot more nitrogen on their dive than I would on mine.

 

[scubadada]

...I don't have a problem with having new divers, who might breathe through their air like a steam train, diving with a computer which is more conservative than mine, as they're probably going to inturn a lot more nitrogen on their dive than I would on mine.

It doesn't work that way

 

[Angelo Farina]

It doesn't work that way

In reality. the Bulhmann adaptive algorithm takes into account exactly these factors such as air consumption and muscular effort. Both cause slightly more Nitrogen absorption...
Uwatec claims to use that adaptive algorithm in their computers equipped with air pressure sensor.
See one of their manuals, it covers this topic extensively: https://www.divestock.com/downloads/dl/file/id/783/aladin_air_z_02_manual.pdf

 

[scubadada]

In reality. the Bulhmann adaptive algorithm takes into account exactly these factors such as air consumption and muscular effort. Both cause slightly more Nitrogen absorption...
Uwatec claims to use that adaptive algorithm in their computers equipped with air pressure sensor.
See one of their manuals, it covers this topic extensively: https://www.divestock.com/downloads/dl/file/id/783/aladin_air_z_02_manual.pdf

There have been previous discussions of the Buhlmann ZH-L8 or 16 ADT MB decompression algorithms on SB. The main problems are a detailed description of how breathing rate, heart rate, and skin temperature are used to adjust the baseline algorithm and validation of the same. Scubapro is the only company using this proprietary algorithm and is the only company, to my knowledge, using "human factors" to increase the conservatism of their decompression algorithm.

 

[rongoodman]

I don't have a problem with having new divers, who might breathe through their air like a steam train, diving with a computer which is more conservative than mine, as they're probably going to inturn a lot more nitrogen on their dive than I would on mine.

Do you have any reason to suspect that inert gas loading is related to a diver's breathing rate, as opposed to just depth and time?

 

[Angelo Farina]

There have been previous discussions of the Buhlmann ZH-L8 or 16 ADT MB decompression algorithms on SB. The main problems are a detailed description of how breathing rate, heart rate, and skin temperature are used to adjust the baseline algorithm and validation of the same. Scubapro is the only company using this proprietary algorithm and is the only company, to my knowledge, using "human factors" to increase the conservatism of their decompression algorithm.

The fact that other companies are not yet capable of accounting for these "human factors" does not mean that they are not relevant...
Personally I think that the workload is a significant factor determining the amount of Nitrogen being captured by various human tissues, particularly when you are still far away from saturation (after 12h, all tissues are saturated at 100%, whatever the workload - you cannot go beyond 100%).
But for short, deep dives, typical of rec diving, most tissues will only be saturated at a few percent. The difference between, say, 5% and 7% is substantial.
I also think that, without other sensors available, using the air consumption as a proxy for workload is a sensible approach. Certainly with an heavy workload the air consumption will increase, hence it is correct to estimate more Nitrogen in the tissue. If the anomalous air consumption was not caused by heavy workload, but for example by a free-flowing reg or from a diver breathing anomalously because he is excited, then there is no risk over-estimating the real Nitrogen load, and reducing the NDL accordingly (or extending the deco stops).
The risk is ignoring the workload effect, and continuing to apply a model which was tuned for light workload even when the workload is heavy: this is not safe enough for me...
On a cheap computer, not capable of employing the advanced methods (and sensors) used by Scubapro-Uwatec for estimating the real workload, the only "safe" solution is to add a proper safety margin to the standard decompression model, allowing for heavier workload.
I prefer to have such an additional safety margin always there, even when not needed, than risking using a computer with less conservatorism, which can cause DCS if, for any reason, my workload is not as light as the standard deco module is assuming...

 

[loosenit2]

Sorry, by my engineering studies here need to kick in. Safety is the result of following the rules, and then taking some "SAFETY MARGIN". The larger this margin, the greater the safety.
If you think to be safe just staying in the edge of the rule, there will be high chances that something goes worse than expected, and you will be hit.

You have made a blanket statement that I don't believe holds up to scrutiny. If I were to follow your advice driving a car on a road, in traffic, with an 80km per hour speed limit then going 79km and hour would be safe but going 40km per hour would be more safe. I believe however that going 40 would make you less safe because your car would be an impediment and would likely get hit by someone going twice as fast as you, going with the flow of traffic in my example is more safe.

Following the same analogy with diving if staying under M values is the rule then applying conservative gradient factor must be more safe right? But the more conservative you make the safety factor the more the profiles begin to look like Deep stop profiles, which, debatably, have been shown not to be safer because you continue to on-gas some compartments doing the deep stop. Again there is a window in conservatism, like going with the flow of traffic, that produces a more safe profile.

 

[Diving Dubai]

As usual SB likes to bicker about the minuta and often misses the point in the desperate attempt to justify that each new diver should rush out and buy a Teric /sarcasm

I will die on the hill that says the priorities for a new diver are a computer that is simple to operate and simple to understand. in the real world only the most diligent will RTFM. I've witnessed people who were confused by their NDL readings - because it was actually deco and they didn't realise. I regularly see owners who have no clue how to change gasses (that's the dive Pro's job, surely?)

Most people are more than happy to leave their computers on default, the vast majority are gas rather than NDL limited. If you're on a vacation with multiple repetitive dives, then diving more conservatively is probably a good thing.

Most problems I've seen with vacation divers stem from over indulgence because they're on vacation burning the candle at both ends, dehydration, not being acclimatized to the high temps etc

Lots of divers fail to realise that their computer doesn't' actually know their N2 loading - it's just a guess, and now some focus is being placed on the slow compartments being the cause of undeserved hits, rather than teh fast compartments which the computers primarily track

@Gary_Ward has a different perspective on reliability based on someone who owns brands that get heavily used. this might not be applicable to someone making less than 100 dives a year

My wife prefers to keep her conservatism high, she cares less about a few extra minutes, despite being qualified she's not interested in deco, but has enough knowledge that she's happier to come shallow early to "off gas" rather than stay down. If its a wreck, her personal interest meter wanes well before her NDL drops

So for new divers my advice is always the same. buy something affordable now that meets your actual and foreseeable needs, because even a little way down the road, your views and tech may change.

But heck, if you can afford a Teric and want one, then I'll happily sell you one of those too