Nitrox course. What's the point?

[dmaziuk]

...
(oh, and yes... I do this to my students also. Not my scuba students, my college students. Most of them just humor me, some ignore.)

I spend so much time on a computer it's faster to just fire up the calculator, yet every once in a while I work out the answer by the time the app starts.

 

[dmaziuk]

Once you are really into decompression, dawdling on ascent can significantly increase your decompression time because while your faster tissues are off-gassing (as I was describing in the last paragraph), your medium and longer tissues are ongassing, and they are increasing your required decompression time.

Your fastest tissue is the one that saturates first at the bottom and therefore the one that controls your first deco stop. On a no-stop dive your first deco stop is the surface. So on an isolated no-stop dive ascent is controlled by the fastest TC and the main issue there is not going up faster than it can off-gas. Once that TC is saturated past no-stop limit, and your first deco stop is below the surface, the game changes and the other tissues (may) come into play. This creates all sorts of "ripples", incl. the too slow ascent problem, disappearing deco obligations, and more.

 

[Blackcrusader]

Once you are really into decompression, dawdling on ascent can significantly increase your decompression time because while your faster tissues are off-gassing (as I was describing in the last paragraph), your medium and longer tissues are ongassing, and they are increasing your required decompression time.

Guilty as charged but then again my computer tells me I am on gassing so get a move on lol.

I am really enjoying reading this thread. Yes I did deco training but stopped doing serious deco planned dives probably 15 years ago.
I'd rather do 3 or 4 dives a day than than do one dive with a 30 minute deco obligation and a long surface interval.

I love my Shearwater Perdix as I set it to OC tec and it does what is does wonderfully. Yes I have brain matter but I let that go into total relaxation and at anytime I can look at my Perdix and see what it tells me. I like the fact if you do light deco you often clear the deco obligation before you get to the deco stop as you ascend. As my eyes were fading from old age ( before I got them fixed ) I love the large display that I can see easily in any conditions and adjust the screen to see what I want to see and one button push to see other info. Have I let myself become lazy? Yes and I enjoy it. I do dive plans on the Perdix. Much easier than tables with small fonts that were getting hard to see lol

Let's face it, computers are accurate and can do calculations in real time much better than humans can. So I'll use my grey matter to look at the marine life and other humans on my dives. Take some photos or video and chill out. Diving for me is my relaxation time.

 

[Neilwood]

Just a little story about that. When I started tech diving, we did not use computers at all. We preplanned the dive and followed the plan using bottom timers as our guide. When two divers in our group of friends got bent, they had no idea why--they had followed the plan perfectly. Well, one of them was using a computer in gauge mode, so he was able to get a profile of the dive. It turned out they had not been nearly as perfect as they thought--not even close. Ascent rates, depths, and stop times were far from perfect. These were educated people, one with a Ph.D in afield requiring a high level of mathematical skill.

I think of that whenever I see people say they don't use a computer and just follow a written plan instead. Since they really have no way of knowing, they really don't know how well they followed it.

That for me is one of the biggest reasons for using a computer - unless you are extremely meticulous in following your dive plan (down to exact ascent rates, hitting stops exactly both at time and depth etc), you could be quite a way adrift from your "plan" and not know it (as your friends discovered). 30 secs here and there on stops (particularly deep stops) or a slower ascent can have a marked impact on tissue loading.

How many divers know exactly how fast their ascent should be to match their plan and how to gauge that in the water. Assuming 10m/min, how many divers will manage to hit the 10m at exactly 1 minute and how many will be 10-15 secs either side of it?

 

[Celt]

That for me is one of the biggest reasons for using a computer - unless you are extremely meticulous in following your dive plan (down to exact ascent rates, hitting stops exactly both at time and depth etc), you could be quite a way adrift from your "plan" and not know it (as your friends discovered). 30 secs here and there on stops (particularly deep stops) or a slower ascent can have a marked impact on tissue loading.

How many divers know exactly how fast their ascent should be to match their plan and how to gauge that in the water. Assuming 10m/min, how many divers will manage to hit the 10m at exactly 1 minute and how many will be 10-15 secs either side of it?

That’s not true, a 10 or 15 sec difference in assent to the first stop isn’t going to make a blind bit of difference to the total decompression schedule (if it did everyone doing deep air dives would be bent) and you’d have to fall asleep to miss half a minute of a stop time. I would kick myself if I missed half a minute. I can time stops to 5 seconds. 30 feet/min. assent used to be 60feet/min.

 

[boulderjohn]

That’s not true, a 10 or 15 sec difference in assent to the first stop isn’t going to make a blind bit of difference to the total decompression schedule (if it did everyone doing deep air dives would be bent) and you’d have to fall asleep to miss half a minute of a stop time. I would kick myself if I missed half a minute. I can time stops to 5 seconds. 30 feet/min. assent used to be 60feet/min.

I can say with a lot of assurance that the most common error made by people who are following tables and no computer is ascending too slowly to the first decompression stop, and I am not talking about being off by 10-15 seconds. In the case noted above, the divers should have reached their first stop in about 30-45 seconds. It took them over 3 minutes, at which time they started counting their stops according to their plan, not realizing that they had in essence added 3 minutes of bottom time to the dive. That was one of their mistakes.

It happens to people with computers as well, but in that case the computer adjusts for it. I was on a dive on which my buddy and I had the same algorithm and dive plan as another pair of divers sitting next to us on the boat, as was communicated to the DM ahead of the dive. As expected, we arrived at the ascent line at about the same time. My buddy and I ascended first, and when we got to our first stop, I looked down and did not see the other pair of divers. I was worried. The first stops were not long, and we did not see them below us until our third stop. We got back on the boat, the next to last group to do so. As we were putting our gear away, the DM came to us to ask about the last group. We assured him they were on the line, but we had no idea what was holding them up. When they finally got on the boat, they told the DM they did not know what had happened. They had arrived at the ascent line at the planned time, but as they ascended, their computers just kept adding deco time. I then remarked that they had done their early ascent very slowly, and one of them looked at me like I was crazy. "You're supposed to ascend slowly!" he said.

 

[Blackcrusader]

I can say with a lot of assurance that the most common error made by people who are following tables and no computer is ascending too slowly to the first decompression stop, and I am not talking about being off by 10-15 seconds. In the case noted above, the divers should have reached their first stop in about 30-45 seconds. It took them over 3 minutes, at which time they started counting their stops according to their plan, not realizing that they had in essence added 3 minutes of bottom time to the dive. That was one of their mistakes.

It happens to people with computers as well, but in that case the computer adjusts for it. I was on a dive on which my buddy and I had the same algorithm and dive plan as another pair of divers sitting next to us on the boar, as was communicated to the DM ahead of the dive. As expected, we arrived at the ascent line at about the same time. My buddy and I ascended first, and when we got to our first stop, I looked down and did not see the other pair of divers. I was worried. The first stops were not long, and we did not see them below us until our third stop. We got back on the boat, the next to last group to do so. As we were putting our gear away, the DM came to us to ask about the last group. We assured him they were on the line, but we had no idea what was holding them up. When they finally got on the boat, they told the DM they did not know what had happened. They had arrived at the ascent line at the planned time, but as they ascended, their computers just kept adding deco time. I then remarked that they had done their early ascent very slowly, and one of them looked at me like I was crazy. "You're supposed to ascend slowly!" he said.

You make good points I never really considered when I did not have a dive computer. I could not possible have known the real time situation on deco dives it was all the pre planned dives on time. My shearwater updates data every 10 seconds. My grey matter cannot keep up with that.

It makes me realize that all my early deco dives without a computer you really do not know if you were on gassing adding more time even though we had watches and followed the dive plan. Dive computers were just coming out but crazy expensive at the time or maybe I just had less money than now lol

Computers are great go to slow it adds what time is necessary and you do not have to try and recalculate. Does that make me a lazy diver or a diver who uses technology to be a safer diver. I always hated bring tables and writing boards and trying to calculate for any changes.

 

[Celt]

I can say with a lot of assurance that the most common error made by people who are following tables and no computer is ascending too slowly to the first decompression stop, and I am not talking about being off by 10-15 seconds. In the case noted above, the divers should have reached their first stop in about 30-45 seconds. It took them over 3 minutes, at which time they started counting their stops according to their plan, not realizing that they had in essence added 3 minutes of bottom time to the dive. That was one of their mistakes.

It happens to people with computers as well, but in that case the computer adjusts for it. I was on a dive on which my buddy and I had the same algorithm and dive plan as another pair of divers sitting next to us on the boar, as was communicated to the DM ahead of the dive. As expected, we arrived at the ascent line at about the same time. My buddy and I ascended first, and when we got to our first stop, I looked down and did not see the other pair of divers. I was worried. The first stops were not long, and we did not see them below us until our third stop. We got back on the boat, the next to last group to do so. As we were putting our gear away, the DM came to us to ask about the last group. We assured him they were on the line, but we had no idea what was holding them up. When they finally got on the boat, they told the DM they did not know what had happened. They had arrived at the ascent line at the planned time, but as they ascended, their computers just kept adding deco time. I then remarked that they had done their early ascent very slowly, and one of them looked at me like I was crazy. "You're supposed to ascend slowly!" he said.

That’s what happens when there’s an over emphasis on not making a rapid assent, how many times do you hear the hype you’re going to die if you come up to quickly, people are going to err on the slow side, but I always done 60feet/min. on navy tables. So I had to slow it down when I started using modern tables and assent rates

 

[Celt]

It makes me realize that all my early deco dives without a computer you really do not know if you were on gassing adding more time even though we had watches and followed the dive plan. Dive computers were just coming out but crazy expensive at the time or maybe I just had less money than now lol

I’m not knocking the versatility of a computer, and they are a marvellous asset to a diver, but that doesn’t mean you can’t make a safe assent without one. Millions of safe dives have been made without one. It’s amazing how quickly previous diving practices can suddenly be declared unsafe in order to sell new gear.

 

[60plus]

In reply to posts 217 & 218. What you say is reasonably accurate, but what I posted is true in regard to the context in which it was posted. Posters were implying that a small variation in % around the 32 % mark was critical which it is not. Ox Tox does not only cause the convulsions that usually result in drowning, there may be no convulsions but longer term damage can occur to other organs.