How much narcosis is acceptable/'normal'?

[Jheard89]

I'm fairly new to technical diving, with roughly 40 dives on CCR up to 60m, with a similar number on OC to a max of 50m.

I've been trained to dive with a max pn2 of 3.16, however I've exceeded this on a few occasions, most recently to 4.125 on a dive to 45m. I've noticed that this is not uncommon, having come across an old thread on these boards in which the majority of posters said they regularly dive to 50m using air.

During my dive to 45m (and CCR dives to 60±) I felt pretty drunk/spaced out, which I wasn't surprised by considering the pn2 I was at. As a relative beginner to tech diving, I don't have much experience with which to gauge what would be deemed as a 'normal' feeling of early symptoms of narcosis vs. when one should start to think about ascending, or diving with mixes containing more helium.

Is this something that just comes with more experience? I guess I'm just seeing all these people dive at a similar pn2 and acting like it's nothing, and wondering if what I felt is normal, or whether I might just be particularly sensitive and should dive more conservatively based on my individual tolerance?

Any feedback would be greatly appreciated.

 

[kensuf]

CO2 heavily influences the effects of narcosis, if you're working hard you're really going to feel it deep. Additionally, while is subjected to the effects of narcosis, some may notice it sooner/quicker than others -- think about going to a bar, some people seem to hold their liquor better than others. That doesn't mean they'll pass a breathalyzer test though.

At the end of the day though, you're on a rebreather, there's no reason not to have helium in your DIL.

 

[Storker]

While most are worried about narcosis, you might want to read up on gas density and CO2 ventilation issues. Interestingly, the depth where gas density issues start to become significant without helium in the mix is in the same depth range where most of us start feeling the narc (i.e. between 4 and 5 ATA depth).

Gas density guidelines

 

[Jheard89]

CO2 heavily influences the effects of narcosis, if you're working hard you're really going to feel it deep. Additionally, while is subjected to the effects of narcosis, some may notice it sooner/quicker than others -- think about going to a bar, some people seem to hold their liquor better than others. That doesn't mean they'll pass a breathalyzer test though.

At the end of the day though, you're on a rebreather, there's no reason not to have helium in your DIL.

Yea that's what I thought. I've always been more sensitive than most to any sort of stimulant/intoxicant, as well as temperature among other things. I guess knowing that I'm more susceptible makes me a bit nervous when it comes to deep diving. I guess it's just a matter of learning your own limits and knowing where to draw the line?

At the moment for the project I'm working on we're on OC and are currently limiting ourselves to 45m due to a shortage of helium in Taiwan.

 

[Jheard89]

While most are worried about narcosis, you might want to read up on gas density and CO2 ventilation issues. Interestingly, the depth where gas density issues start to become significant without helium in the mix is in the same depth range where most of us start feeling the narc (i.e. between 4 and 5 ATA depth).

Gas density guidelines

I hadn't thought about that. Thanks for the suggestion. So I guess I could have just as easily been feeling the effects of mild hypercapnia and not necessarily narcosis? Makes sense as there was a strong current on the surface as we descended down the line which got my heart rate up. The symptoms definitely subsided somewhat (although not completely) after I was able to relax at the bottom.

 

[wedivebc]

keep in mind that with a setpoint of 1.2 you will be exposed to higher nitrogen pressure at 45m (155ft) than if you were diving air to the same depth.

 

[Celt]

what is acceptable to some may not be acceptable to you. when you reach your max depth on a deep air dive there is a sudden nitrogen hit. this fades after a minute or two and the narcosis then builds gradually depending on the work effort and time spent at depth. Bad vis and cold will add to it. Once you start to ascend the narcosis immediately subsides. Thats how it is for me and only you know how it will affect you everyone is different.

 

[Storker]

when you reach your max depth on a deep air dive there is a sudden nitrogen hit. this fades after a minute or two

Allow me to disagree. It's highly personal.

Just this spring, I had this dive. We descended fairly quickly to some 25-30m, then levelled out and found the wreck. After puttering around the wreck a little, I realized that I was more narked than I appreciated. That was a little more than "one minute or two" after reaching our max depth. Fortunately, I had a good buddy and was able to realize that I was impaired and should ask my buddy to take the lead.

 

[Celt]

Allow me to disagree. It's highly personal.

Just this spring, I had this dive. We descended fairly quickly to some 25-30m, then levelled out and found the wreck. After puttering around the wreck a little, I realized that I was more narked than I appreciated. That was a little more than "one minute or two" after reaching our max depth. Fortunately, I had a good buddy and was able to realize that I was impaired and should ask my buddy to take the lead.

I thought he said 50m and thats why i finished my post by saying thats how it effects me and everyone is different

 

[rjack321]

For me, the deeper I go the LESS narcosis is acceptable. I am probably not going to get my undies in a twist diving air or nitrox at 40m = END 40m

If I'm at 80m there's no way I want an END of 40m, that's crazy. (and the density guidelines support this). The consequences of not having a clear head are way more severe. By 60m I want ENDs <25m, at 80+m I want ENDs around 20m max.