First Dive Trip Without Instructor - Need to Rent Gear & Help Planning

[jadairiii]

You really should consider a Nitrox course. And if you are Nitrox certified, go get your money back from the dive shop.

 

[Storker]

Why does it seem people are saying "you don't need nitrox, it's not that deep" when nitrox isn't for "going deep" but for spending more time underwater?

There are two things limiting your bottom time: your NDL and your min gas time. Sometimes, its your NDL that limits your bottom time, sometimes it's your min gas time that limits your bottom time. If you're on EAN, it's (IME) usually your min gas time that's limiting. If you're EAN and cavern certified, I'm a bit amazed that you aren't aware of this.

 

[Storker]

Why would anyone not want to dive nitrox so long as they will not exceed its max depth?

We who dive nitrox usually do it because we don't enjoy the concept of riding the NDL, but prefer to stay a little away from it. However, if nitrox is ridiculously expensive, or if the profile keeps us well away from the NDL even on air, there is no good reason to opt for nitrox.

EDIT: And this comes from someone who uses EAN32 as his standard gas, even on shallow bimbles

 

[Storker]

Oxygen toxicity has no time requirement.

Get a refund on your nitrox class, because you obviously haven't gotten the required learning outcome. There's CNS toxicity (not particularly time related) and there's pulmonary toxicity (time related). In NDL diving, pulmonary oxtox usually isn't an issue, but if you aren't aware of the issue, you really aren't competent to dive nitrox.

 

[boulderjohn]

Why does it seem people are saying "you don't need nitrox, it's not that deep" when nitrox isn't for "going deep" but for spending more time underwater? Why would anyone not want to dive nitrox so long as they will not exceed its max depth?

Yes, it is for spending more time underwater, but that only matters within a certain depth range. It really does not make any difference in shallow diving. If you were to dive on air to 40 feet using the PADI tables, you would have a maximum bottom time of 140 minutes. If you were to dive EANx 32 to 40 feet using the PADI nitrox tables, you would see they don't even bother putting 40 feet on the table. It starts at 45 feet, and you get 220 minutes. That is certainly more time allowed, but are you going to do a dive for 220 minutes? Are you going to do a dive for 140 minutes? In contraast, if you are talking about 70-100 feet, you will see numbers that make sense for using nitrox--at 90 feet on air, you get 25 minutes, but with EANx 32, you get 35 minutes.

I don't think I am confusing those. Boulderjohn posted that you can dive "all day" (measure of time) at rec depths using EANx32. I was checking the dive tables and saying that there are still time limits with EANx 32.

Yes, you were confusing them. I will take the blame for that, because I assumed you would see the difference without the full explanation and so waws not clear enough.

Your dives are always limited by no decompression limits. You do get longer dives with nitrox, as stated above, but you still are limited by those longer NDLs. I, my post, however, I was responding to your question on whether it was safer to use air or nitrox. If you take a standard nitrox course, the answer will be that it depends upon what you were talking about. With nitrox, one safety concern is oxygen toxicity. I was pointing out that at the depths you will find at that site, you will have no concerns about oxygen toxicity no matter how long you dive, so that safety issue is off the table. That does not mean, however, that you get to ignore NDLs.

 

[Storker]

Your dives are always limited by no decompression limits.

No, they aren't. Sometimes - and under some conditions - they are limited by min gas time.

 

[boulderjohn]

No, they aren't. Sometimes - and under some conditions - they are limited by min gas time.

I did not say your dives are ONLY limited by NDLs.

 

[Storker]

I did not say your dives are ONLY limited by NDLs.

No, you didn't, but in the quest for clarity I wanted to clarify that point.

 

[CavernFrog]

Well, obviously I need to learn more about the varieties of issues associated with Nitrox. I did however only miss one question on the PADI Nitrox exam and a lot of the issues you guys are mentioning are barely covered in the PADI materials.

As far as I know, the main issues I need to be aware of are:

1. NDL - time remaining at a particular depth due to nitrogen absorption
2. Gas time - time remaining till required turn-around at current consumption including the desired reserve
3. MOD - maximum safe depth for the O2% in my gas

I have learned from this conversation, not from the PADI Nitrox course materials, that there are time-based forms of oxygen toxicity that become important to consider when diving multiple dives per day over several days. I am always open to learning and so I appreciate the new information.

 

[CavernFrog]

I also understand that for some shallower depths, Nitrox may not give you much benefit in terms of extended NDLs, however, I feel like it still is at least a little bit safer than air.