Middle ground charters and Nitrox

[Spearfish20]

Sorry, not sure if this is the right place to put this and is a little longwinded, but hear go. I am a PADI AOW diver, have been diving for about 17 years, have recently obtained my PADI nitrox card (21%-40%), and have a hand full of deep dive under my belt (all on air). I have always wanted to dive the middle grounds out of Florida, where I group but never got the chance to. I am planning a trip back to Florida and am going to try to make this happen. All the boats I have seen that advertise trip to the middle grounds require or strongly suggest being nitrox certified. According to the nitrox table a 32% mix @ 1.4Po with a depth of 110ft and everything I have seen on the middle grounds states that most dive sites are in the range of 85ft – 140ft in depth. So I don’t see how that nitrox is safer then air in this depth range of 110ft to 140ft and why the charters boats are pushing this. In other destinations such a Cozumel I have dove the first deep dive on air and the next three dives on nitrox, but that does not seem to be the case on the middle grounds charters they dive all nitrox. I have heard tri mix is the safest but do not have the train (yet) to dive tri mix gasses and would like to avoid bring that in to this discussion if we could. So my question is why are these boat chatters require or strongly suggest that divers be nitrox certified. Can someone help me understand this? Thank you in advance for helping me get to the bottom of this.

 

[vjanelle]

Well, you don't have to use 32%.. You could use 30, 28, etc. Plan your dives, then get an appropriate mix for that dive.

It's not that it's "safer" than air (although incidents of DCS are sometimes lower on liveaboards that encourage it), it's that it gives you a longer bottom time. Why go out on a boat and travel all that way if you're going to have a 10 minute bottom time?

 

[rjack321]

Well, you don't have to use 32%.. You could use 30, 28, etc. Plan your dives, then get an appropriate mix for that dive.

Agree 32% is probably not the best choice. Something like 26 or 28% would be better. These give you roughly 5 to 8mins more NDL time on the bottom. Without this buffer and with repetitive dives you're going to go into deco. And with all the fish & fish blood in the water in the middle of nowhere you probably don't want to go into deco.

It's not that it's "safer" than air (although incidents of DCS are sometimes lower on liveaboards that encourage it), it's that it gives you a longer bottom time.

Its safer assuming you stay at an appropriate ppO2 and use air tables.

Why go out on a boat and travel all that way if you're going to have a 10 minute bottom time?

Because the middle grounds is mostly for spearfishing. Shoot your fish and ascend so you don't go into deco and can have more bottom time on the next dives to shoot more fish.

 

[1_T_Submariner]

I agree with they probably don't use 32% probably something less. Might want to check before you go?