Decompression Stop Guidelines - What we have to do if got deco alert?

[Belzelbub]

How difficult it is to follow the instruction given by your own computer?

Based on numerous threads here, it's apparently quite difficult. I find it truly shocking to dive with a DC, but not understand what it's trying to tell you.

Navigating the menus and changing settings can be a challenge on some computers, but understanding the dive screen should be the first thing when getting a new computer. Rental computers can be a challenge as the diver is constantly having to learn different interfaces. However, the rental shop should go through the basic operation, and it's on the diver to make sure they understand it.

 

[boulderjohn]

One reason that people do not understand their computers is that their manuals are too hard to read. My first computer was a Suunto, and because my OW training had been table-based, I had no way of knowing what features to expect when I started reading the manual. The information I needed to use the computer constituted about 5% of the total content of the manual, and it was scattered about, buried in the information I didn't need to know.

Once on a day where a group of us were dong multiple dives in no particular order, a member of our group said upon surfacing that during the dive his Suunto computer had started acting strange. When he described it, I realized he had gone into deco during the dive and had blown off the deco stop. I immediately took him down to 15 feet. His computer was already in error mode, so it was worthless. We stayed about 15 minutes before surfacing. He didn't have any problems.

 

[BlueTrin]

I had issues understanding what would happen if I break the NDL with my first suunto by reading the manual too.

 

[Belzelbub]

One reason that people do not understand their computers is that their manuals are too hard to read.

True. I was thinking this as one contributor as I was typing this. It's a contributor, no doubt. But still inexcusable.

The manuals for my Oceanic computers were OK. They weren't the best, but were usable. They also included a quick start to get to the basic operations. The Perdix manuals are great. Very easy to read, and easy to understand. The Garmin manual was also pretty good. Contained a lot of information, which is understandable as there are a lot of activities besides diving to be explained. Diving sections were easy enough to understand. I've never owned or used a Suunto, so that may be a whole different beast.

All that said, if the diver doesn't understand the tool they are using, they shouldn't use it. Taking a computer along on a dive doesn't actually help to keep you safe. Understanding what it's trying to tell you, and making necessary adjustments can help to keep you safe.

 

[BlueTrin]

@Belzelbub i think if you talk to a few random newly certified divers, it will be a shock to realise that many (if not the vast majority) will have no clue about what happens if you break the NDL on their computer and what they should do and how the stops will be displayed with ceilings and time left on their computer.

That will include people like me who are fairly technical in their job and tried to read the manual.

The reason is that I wasn’t taught OW on a computer or given clear instructions about what to do/expect if you break accidentally the NDL.

 

[Belzelbub]

@Belzelbub i think if you talk to a few random newly certified divers, it will be a shock to realise that the vast majority will have no clue about what happens if you break the NDL on their computer.

I don't doubt that at all. I don't do a lot of dives with newish divers, but have seen this when doing training dives (mine or my daughters') at popular dive locations.

The reason is that I wasn’t taught OW on a computer or given clear instructions about what to do/expect if you break accidentally the NDL.

My OW course didn't involve any computer training either. We used tables. This was covered in some respect in my daughters' courses, but I can understand why this won't be covered in a lot of detail during an OW course. So many different computers available, I wouldn't expect the instructor to be knowledgeable on them all. At best, they may have some familiarity with the brands the shop they may work out of sells.

 

[boulderjohn]

My OW course didn't involve any computer training either. We used tables. This was covered in some respect in my daughters' courses, but I can understand why this won't be covered in a lot of detail during an OW course. So many different computers available, I wouldn't expect the instructor to be knowledgeable on them all. At best, they may have some familiarity with the brands the shop they may work out of sells.

The standard PADI OW table-based course taught students what to do if they violated NDLs with a table. It did not teach what to do if you violated with a computer, since computers were not part of the course. Consequently, you have something mentioned in the origin of this thread--people being told that if they violate NDLs with a computer, they should follow the rules for violating NDLs with a table. Students taught that way can be logically excused for not searching through the manual to find out how the computer deals with decompression stops.

The computer version of the course does not teach a specific computer. It talks about how a generic computer functions. It has an online interactive simulator in which you can move a generic computer through a variety of diving scenarios to see how it works during a dive. For NDL violations, it tells the student to follow the computer's instructions. When done with the course, a student purchasing a computer should be able to go through the manual in search of the specific functions that were covered in the course.

 

[scubadada]

The effect of a decompression algorithm on a no stop vs. a decompression dive deserves to be emphasized.

The following table lists the NDLs for a first, clean dive to 70 ft on 32% nitrox. DSAT and Buhlmann with a GF high of 95 are generally considered liberal. PZ+ and Buhlmann with a GF high of 85 are generally considered moderate or middle of the road. Buhlmann with a GF high of 75 is generally considered conservative. I only have Oceanic and Shearwater computers to obtain NDLs from the planning function. If you have another brand of computer, with a different decompression algorithm, you can obtain and compare your NDLs from your dive planner. RGBM computers, Suunto, Cressi, Mares, tend to be in the moderate to conservative range, more conservative on repetitive dives.

I dive two computers, one running DSAT and one running Buhlmann with a GF high of 95. Assuming we both have enough gas, if you are diving PZ+ or Buhlmann at a GF high of 85 or 75, you are going to exceed your NDL and go into decompression well before I would. So, we dive for an hour, is this a deco dive? For me, no, for you, yes. You should follow the recommendation by the computer you chose to dive with and satisfy the decompression obligation you are given.

If you complete your decompression, you will be able to continue diving, uninterrupted. If you skip your decompression obligation and are diving an Oceanic, Aqua Lung, Suunto, Cressi, Mares, or many other computers, you will be locked out from using your dive computer for 24-48 hours. If you are diving a Shearwater computer, you will be informed of your violation and will decide yourself whether to continue diving or not.

So, we did our hour dive with mine being no stop and yours being a deco dive. We surface together with you violating your deco obligation. Are you at high risk for DCS? That's a good question that comes up on SB.

A dive computer's decompression algorithm is one important variable in choosing one for use. It behooves us all to have a reasonalbe understanding of this topic.

 

[johndiver999]

One obvious solution seems to be to teach people how to use their computer to do a decompression dive and then tell them not to do it. Which is how the tables were taught, right?

 

[tursiops]

One obvious solution seems to be to teach people how to use their computer to do a decompression dive and then tell them not to do it. Which is how the tables were taught, right?

No, decompression diving was never taught on the RDP, only on Navy or similar tables. For the RDP, there was only the "emergency decompression" protocol for exceeding one's NDL by less or more than 5 minutes.