Dedicated Nitrox equipment

[DA Aquamaster]

The threshold for oxygen toxicity symptomst starts at a PO2 level of 1.10 ATA

A PO2 level of 1.40 ATA is the level at which oxygen presents a moderate risk to divers. This is the maximum recommended limit for normal recreational divers. MODERATE risk does not equal perfectly safe in my books. This is from the SSI EAN Nitrox specialty manual.

That is correct, but the same manual also lists 1.4 as the "recommended limiting PO2 for recreational divers" and there are some pretty solid reasons for this.

Determining your max PO2 with nitrox can be regarded as a balancing act where you are playing the reduced risk of DCS on a given profile with the increased risk of Oxtox.
From a practical standpoint however, you have a 150 minute single dive limit at a PO2 of 1.4 and a 180 minute cumulative limit over a 24 hour period. That's a lot of time at 95ft on 36% or at 110 ft on 32%. Even at a PO2 of 1.6, you still have a 45 minute single dive limit and a 150 minute 24 hour limit which is still an awful lot of time at 110-130 ft.

And those exposure limits are based on NOAA working diver limits that are both conservative and do not given any real credit for surface intervals. Plus, unless you are diving square profiles at the MOD, you are not going to be exposed to this PO2 for most of the dive anyway, which again adds a large safety factor to the CNS clock.

So in practice a PO2 of 1.4 is a very reasonable limit for the working portion of the dive or for recreational divers. You can try to make it "safer" by limiting the PO2 to 1.3, 1.2 or 1.1, but it's debatable whether you are adding any real safety or just increasing the amount of nitrogen you are going to have to offgas on a given dive and in effect increasing your DCS risk.

But that is the nice thing about nitrox, you can choose to do it any way you like.

 

[Canadian_Diver]

Yes, true on all accounts.

One thing that NOAA doesn't take into account for, and nor do the dive tables, or dive computers, is that each person is physiologically different.

It's a balancing act, and it all comes down to good dive planning, following your profile, and knowing your physical limitations.

I always tend to lean to the conservative side, it doesn't guarantee that I won't get DCS, Narced, or OxTox ... but it allows for a bit of forgiveness.

As you said, EAN is a wonderful thing, and can be used to benefit you in a number of ways. It's all personal preference in how you use it to get the desired benefits.

 

[Diver Dennis]

Yes, true on all accounts.

One thing that NOAA doesn't take into account for, and nor do the dive tables, or dive computers, is that each person is physiologically different.

It's a balancing act, and it all comes down to good dive planning, following your profile, and knowing your physical limitations.

I always tend to lean to the conservative side, it doesn't guarantee that I won't get DCS, Narced, or OxTox ... but it allows for a bit of forgiveness.

As you said, EAN is a wonderful thing, and can be used to benefit you in a number of ways. It's all personal preference in how you use it to get the desired benefits.

Most dive computers allow you to set them up to be substantially more conservative than the base settings.

 

[Canadian_Diver]

Most dive computers allow you to set them up to be substantially more conservative than the base settings.

Yup. My Genesis ReactPro is on the somewhat conservative side to begin with.