Computers that don't lock out tangent.

[dmaziuk]

please read up on the physiology that is going on with this and the reasons that computers will lock out. Blowing safety stops counts with some, having too rapid of an ascent counts, neither of which mean you actually hit NDL.

I've never seen one actually named, that locks you out for omitted optional stop. RGBM may (seems to) penalize you on the next dive for it, but not lock out.

Ascent rate violation can be an actual problem: ascent time, specifically off-gassing during ascent, is factored in when computing the NDL. If you blow ascent rate, you can "blow the NDL" -- as in go over the M-value on your way up even though your computed NDL was non-zero at the start of the ascent.

Ascent rate may affect bubble formation voodoo in RGBM and/or VPM, but I would expect them to penalize you on the next dive. Unless you actually "blow the NDL" as per the above.

A purely separate ascent rate alarm that has nothing to do with the gas loading model could lock you out if it was designed by the lawyers. I have not heard of one. Doesn't mean they don't exist, of course.

 

[tbone1004]

@dmaziuk pretty sure Suunto's will get angry of you omit a full safety stop, but haven't encountered it since I refuse to dive them.

 

[RonR]

I can say what our thinking was around this issue in developing the Atomic Cobalt, and why we do not “lock out” divers.

The fundamental problem is that violation/ no violation is a binary choice, while all decompression calculations are, to paraphrase Erik Baker, an attempt to draw a bright, clear line through a fuzzy gray area.

When developing a computer you need to clearly define specific parameters where you call a violation. There are various strategies- some just use time above a stop depth without completing the stop, but that can risk triggering too rapidly or not alerting soon enough. We implemented what amounts to another algorithm- one that looks at the stop depth, time away from the stop, the % of the distance to the surface reached above the stop, and the total deco schedule, and that algorithm determines if a violation is logged. We try to avoid spurious violations while quickly warning when someone is truly missing a required stop- not waiting two minutes, say, if they are just blowing stops.

But in real world terms it’s possible for a diver to exceed these parameters slightly- it’s a fuzzy area. Maybe if their conservatism were set slightly differently a violation would not have been logged. Maybe they missed 30 seconds of a 50' stop, and spent extra time at the next one. Our solution is to warn the diver, to plaster a big warning sign up on the screen for 24 hours, but not to prevent the computer from working normally (other than showing a warning). This lets the diver decide if their violation is something they are willing to consider trivial. They might choose to dive a little more conservatively, or might choose to sit out a day. We warn, but the decision is up to them.

Ron

 

[dmaziuk]

@dmaziuk pretty sure Suunto's will get angry of you omit a full safety stop, but haven't encountered it since I refuse to dive them.

Well that's kinda my point: everyone's account I actually read here is either "but I'm not diving one" or "because I forgot to change the O2%" or "because she accidentally set it gauge mode" etc.

Zoop's manual, OTOH, says "every dive over 10 meters the instrument has a three minute countdown for the recommended safety stop...If it is ignored, there is no penalty". But then there is a "mandatory safety stop" that "when the ascent rate exceeds 12 meters/min [40 ft] momentarily or 10 meters/min [33 ft] continuously the micro-bubble build-up is predicted to be more than allowed for in the decompression model. The Suunto RGBM calculation model responds to this by adding a Mandatory Safety Stop to the dive. The time of this Mandatory Safety Stop will depend on the severity of the ascent rate excess." If you blow that one, "the dive computer shortens the available no-decompression time for your next dive".

If you go over the NDL and have a mandatory decompression stop then "if you ascend above the ceiling during a decompression stop ... an error
warning Er reminds you that you have only three minutes to correct the situation. If you continue to violate the decompression, the dive computer goes into a permanent Error Mode. In this mode the instrument can only be used as a depth gauge and timer. You must not dive again for at least 48 hours."

 

[dmaziuk]

It seems if you omit a deco stop the computer model would become invalid for further diving right?

Depends on the model, I suppose, but the basic on/off-gassing part doesn't really care. The implementation, especially on very low-power devices, may: e.g. one common trick is replacing heavy calculations with a pre-computed lookup table, but then if you're off the table, all your numbers are indeed invalid.

 

[loosenit2]

There are other annoying situations where a computer will lock you out without good cause, for example putting computer into gauge mode.

I covered this in a different thread but on a 2 tank trip with my daughter. On the second dive of the day she messed up and put it into gauge mode rather than dive mode. We worked through that because we had checked NDL limits prior to dive and stayed within them for the dive. We finished that dive at 1200 and went out for a dive the next day at 0830 to find the computer still locked out, it had imposed a 24 hour lock out. That is a 19:30 SI between dives, her tissues were clear, even using ultra conservative DAN no fly times she could have flown, but computer was locked out for 24 hours. Thank goodness I had a backup computer for her to use.

My perspective is that this is an unrealistic lock out condition. Did not realize the computer did this before I bought it or I would have thought twice.

 

[Ghost95]

Thanks for the replies all. It is interesting. I guess I'm still looking at this from a recreational point of view. Back in the day there were divers, and yes I saw this with my own eyes, who would cut a stop short by a min or two due to insufficient gas supply, being impatient, or the need for a cigarette. The computers they were diving would get mad when they got to the boat so they would send them down on a fishing line to "clear" them and make a second or third dive. I didn't see any of them get bent that way but it seemed like a really, really bad idea. These were not students just other people I dove around with. Situations like this were what was going through my mind when I asked the question.

This makes sense when looking at the above scenario.

That said, it is also much more dangerous to have the lockout as there are many reports of divers getting locked out and then ignoring it and diving anyway. Much better to have a computer that is tracking everything and trying to keep you safe versus one that says "tough luck, if you want to dive again I'm not going to do anything for you other than count depth and time, hope you don't die"

Now, I'm sure there are holes in my understanding of decompression theory but I thought that once bubbles form, even micro bubbles, they don't dissolve and off gas the way normally dissolved gas in tissue does, hence the long chamber rides for bendy people. Also, can't the micro bubbles act as sort of a nucleus for larger bubbles to form up on?

If that's is correct, it seems that omitting a deco stop or rapid ascents could lead to these micro bubbles, that may be asymptomatic, forming. Now if you start another dive with the micro bubbles in your tissues, wouldn't that, invalidate (for lack of a better word) the model because the computer model assumes no bubbles from the start and tries to keep it that way?

Basically, if you ascend to fast, or bypass a required deco stop you're increasing the chance that you have developed these bubbles that don't react the same way as the gas that's dissolved in the tissues. Does a computer model/algorithm continue to treat the gas/tissue the same or does it assume you've got bubbles and adjust the model for the reabsorption and off gassing of those even though they don't react the way normally dissolved gas does? If not, I see the reason for lock out as the model wouldn't be compatible with formed bubbles already in circulation or in tissues.

Clearly the tech stuff is another world and it's voodoo gets spooky down there.

Thanks for all the replies guys.

 

[Ghost95]

Ok, this clearly makes sense. Thanks.

There are other annoying situations where a computer will lock you out without good cause, for example putting computer into gauge mode.

I covered this in a different thread but on a 2 tank trip with my daughter. On the second dive of the day she messed up and put it into gauge mode rather than dive mode. We worked through that because we had checked NDL limits prior to dive and stayed within them for the dive. We finished that dive at 1200 and went out for a dive the next day at 0830 to find the computer still locked out, it had imposed a 24 hour lock out. That is a 19:30 SI between dives, her tissues were clear, even using ultra conservative DAN no fly times she could have flown, but computer was locked out for 24 hours. Thank goodness I had a backup computer for her to use.

My perspective is that this is an unrealistic lock out condition. Did not realize the computer did this before I bought it or I would have thought twice.

 

[loosenit2]

Thanks for the replies all. It is interesting. I guess I'm still looking at this from a recreational point of view. Back in the day there were divers, and yes I saw this with my own eyes, who would cut a stop short by a min or two due to insufficient gas supply, being impatient, or the need for a cigarette. The computers they were diving would get mad when they got to the boat so they would send them down on a fishing line to "clear" them and make a second or third dive. I didn't see any of them get bent that way but it seemed like a really, really bad idea. These were not students just other people I dove around with. Situations like this were what was going through my mind when I asked the question.

This makes sense when looking at the above scenario.


Now, I'm sure there are holes in my understanding of decompression theory but I thought that once bubbles form, even micro bubbles, they don't dissolve and off gas the way normally dissolved gas in tissue does, hence the long chamber rides for bendy people. Also, can't the micro bubbles act as sort of a nucleus for larger bubbles to form up on?

If that's is correct, it seems that omitting a deco stop or rapid ascents could lead to these micro bubbles, that may be asymptomatic, forming. Now if you start another dive with the micro bubbles in your tissues, wouldn't that, invalidate (for lack of a better word) the model because the computer model assumes no bubbles from the start and tries to keep it that way?

Basically, if you ascend to fast, or bypass a required deco stop you're increasing the chance that you have developed these bubbles that don't react the same way as the gas that's dissolved in the tissues. Does a computer model/algorithm continue to treat the gas/tissue the same or does it assume you've got bubbles and adjust the model for the reabsorption and off gassing of those even though they don't react the way normally dissolved gas does? If not, I see the reason for lock out as the model wouldn't be compatible with formed bubbles already in circulation or in tissues.

Clearly the tech stuff is another world and it's voodoo gets spooky down there.

Thanks for all the replies guys.

You are not alone in not having an understanding; bubble models and decompression as a whole are far from settled science. We still do not truly understand bubbles and DCS enough to have a model that predicts when DCS will occur. What we have are probabilistic models based on empirical observations. In XX number of dives this dive profile has an XX probability of resulting in DCS.

 

[Diving Dubai]

certain computers can/will lock you out for rapid ascent, skipped safety stop etc,

I would like to know precisely which computers lock you out for safety violations as well as deco violations. I can't think of any

The most I've seen, is for a missed Safetly stop, or a fast ascent at very shallow depths 6m /19' and there you just get an annoying bleeping to descend or ignore.

A Suunto and Cressi will give you annoying alarms but not lock out (these I know from actual experience, I'm fairly certain the rest of the entry computers are similar

I think it's important for others to distinguish fact from guess work.

Personal as you know my Eon will lock me out, for Deco violations, but in almost 1000 dives it never has. But I rarely make dives greater than an hour and currently 60m is my max depth. The reason it hasn't locked me out is quite simple because I abide by the deco requirements

Now I do fully appreciate that some divers making seriously big dives with huge deco need options and no possibility of lock out. Some OSTC computers run Buhlmann & VBM concurrently and you can switch between them mid div.

In an "emergency" you can choose which algorithm will get you to the surface the quickest. BUT it's important (for others) to understand, that you do need to have a good understanding of what's happening to be able to make an educated choice knowing the implications of your decision in such a situation.

My personal view, and one I'm yet to be persuaded from is this:

If a diver is worried about, or has actually locked out their computer for a violation, then they are more than likely not experienced , knowledgeable nor competent enough to be diving a non lock out computer at their current level of diving.