Nitrox: No Decompression Limit - Ascent

[Lateralus]

I'm getting a little confused on how to ascent with Nitrox in relation to decompression limits. I recently got Nitrox certified and I'm still trying to grasp the concept of decompression limits.

Is the ascent with air the same as Nitrox? I asked this because I keep getting all these readings on my dive computer when diving Nitrox. When I'm on Air, I gradually ascend and do the safety stop. It's not that much thinking involved. Just monitor your depth, air consumption, etc... With Nitrox I get confused with the Deco limits.

I went on a dive today with Nitrox. Depth was 100 feet. My Nitrox mixture was 33%. I know I'm not supposed to pass 100 feet or the mixture can get toxic. I inputted that data into my dive computer. I believe I failed with the input of the Partial Pressures so this could be a reason why my new computer was giving me all these reading. I got all these deco readings on my dive comp. I don't get what I was doing wrong. I've dove over 50 times already, the majority on air, and this dive was no different than the others. Does that deco mean I'm ascending to rapidly? Am I supposed to stay deeper at that depth, go up, was I in danger? I'm getting confused because sometimes I saw 99 minutes. No way in hell I'm supposed to stay down that deep. So I got confused. For a second there I thought I had to end the dive.

I'll be the first to tell you and I need to read up on using my dive computer, but just want to make sure I'm not missing anything else.

Just want to avoid getting Decompression sickness.

Thanks for the help.

 

[Nick Steele]

What was your dive time? Square profile or graduate ascent?

 

[DogDiver]

Also, 33% is a pretty hot mix for 100 feet. Sounds to me you put yourself past the no decompression limits and your dive computer went into decompression mode as it should have.

 

[hroark2112]

33% is just fine for 100 feet.

My thought here is that you need to learn how to properly use your computer. The PO2 setting in your computer is just an alarm, it doesn't actually change anything with regards to your no-decompression limits. Your no-deco limits are based on the nitrox mix, your depth and time, and previous tissue loading. Take some time and educate yourself on how to properly use and read your computer.

As far as ascent rate, stick with 30 feet per minute and you'll be fine.

 

[Lateralus]

What was your dive time? Square profile or graduate ascent?

46 minutes.

It was a wall dive. The drop point was 40' below the boat, then we made our way to the dropoff. 100' was the deepest we went. I was only there for a few. Then we gradually made our way back. This is when I started to get confused with my dive watch.

 

[mi000ke]

At pp02 of 1.4 and EAN33 you should be good to about 105 feet. If you entered the wrong pp02, then you know what you did incorrectly. In general, as long as you respect the MOD, your dive should be essentially no different than on air, except you might notice greater NDL time depending on your dive profile.

 

[The Chairman]

Is the ascent with air the same as Nitrox?

Yes.

You probably went into deco accidentally. As you get more comfortable in the water, your SAC improves allowing you to stay down longer. With air, you would have had a longer deco obligation. What PDC are you using?

 

[Kayakingphotos]

What model is your dive computer? If you bought it at your LDS, go there and tell them you are confused with it and have them explain it to you hands on. On my computer, if I have an ascent rate violation, it will give me a ceiling and indicate I have to stop for a bit. Somewhat confusing the first time it happened.

 

[boat sju]

I'm getting confused because sometimes I saw 99 minutes. No way in hell I'm supposed to stay down that deep. So I got confused. For a second there I thought I had to end the dive.

As you ascend your NDL time will increase. I suspect when you got to the top of the wall or closer to your safety stop depth your NDL went to 99 minutes. That means you could stay at that depth 99 minutes before entering deco. Is the computer new to you?

boat

 

[Lateralus]

Yes.

You probably went into deco accidentally. As you get more comfortable in the water, your SAC improves allowing you to stay down longer. With air, you would have had a longer deco obligation. What PDC are you using?

I never went into deco. My computer was just telling me all sorts of reading. I think I need to understand this computer better.