Nitrox question

[naplestreasures]

OK folks, I'm looking for an analogy here.
Trying to explain the philosophy of how nitrox increases bottom time..... BUT.......only if you have the gas to use.

Example: If you burn an 80 of regular air in 45 minutes, you will burn an 80 of nitrox I or II at the same rate.
The only difference is that you have less residual nitrogen after the dive.

I'm trying to explain this to my daughter but she's stuck at the BUZZ words...INCREASED BOTTOM TIME...thinking that she'll get longer dive times from the same amount of gas.

I tried to explain that as she dives more and gets a better breathing pattern, she'll use less air and eventually she'll have air remaining after dives where she's reached her max bottom time.
That's when you'll be able to stay down longer hence the longer bottom times.

Any good analogies out there to explain this?

 

[mislav]

Take a dive to 30 meters of depth for instance. On air you have 20 minutes of maximum bottom time before you hit no deco limit. On EAN36 you have 35 minutes.

That's 15 minutes more! Ergo - increased bottom time!

 

[timegan]

Can't see why your daughter doesn't understand. Does she also understand that the deeper you go the denser her air/nitrox, and the more she will use with every breath. Anyway you asked for an analogy......so what about gas (for cars). Let's say you get 25 miles to a gallon, you can fill up with CHEAP??? regular LOL.....but you can splurge and fill up with SUPER gas......but you will still only get 25 miles per gallon no matter. Show her what SAC and RMV mean and how to use them in dive planning. She may understand much more, and it won't hurt yourself to study as well. Hope this helps

 

[Meng_Tze]

Simple analogy:

Given same depth, SAC, etc.

You have a bucket (your body tissues) that can hold 100 balls (Nitrogen max loading before decompression obligations).

You fill the bucket with a rate of 5 balls per minute (Air), it takes 20 minutes to fill the bucket.

You fill the bucket with a rate of 3 balls per minute (Nitrox), it takes 33 minutes to fill the bucket.

With Nitrox, you load less nitrogen in the body. Less nitrogen loading means more time before the tissues are loaded.


There is a bit more to it than that, but for the purposes of understanding N2 loading, this should suffice.

 

[Ann Marie]

OK folks, I'm looking for an analogy here.
Trying to explain the philosophy of how nitrox increases bottom time..... BUT.......only if you have the gas to use.

Example: If you burn an 80 of regular air in 45 minutes, you will burn an 80 of nitrox I or II at the same rate.
The only difference is that you have less residual nitrogen after the dive.

I'm trying to explain this to my daughter but she's stuck at the BUZZ words...INCREASED BOTTOM TIME...thinking that she'll get longer dive times from the same amount of gas.

I tried to explain that as she dives more and gets a better breathing pattern, she'll use less air and eventually she'll have air remaining after dives where she's reached her max bottom time.
That's when you'll be able to stay down longer hence the longer bottom times.

Any good analogies out there to explain this?

Hi and welcome to ScubaBoard!

Well, your daughter is right; she will get a longer dive time or increased bottom time BUT it doesn't mean that she'll get to use that increased bottom time.

You have two credit cards:

Regular credit card (air limits): $5000 limit

Gold credit card (enriched air limits): $10,000 limit

Yes, you get more spending money with the Gold Card, but if you don't have the money to pay it off that extra $5000, that gold card isn't going to do much for you!

 

[mksmith713]

I like the credit card analogy.

 

[SteveAD]

Not an analogy, but this may well help her to understand the concept better:

No Deco Limit on the PADI air RDP for 35 feet is 205 minutes.

I don't know anyone who can make an 80 last 3 hours and 25 minutes at 35 feet. So actual limiting factor is gas supply.

Available bottom time is limited by NDL and gas supply, when either runs out, you're done.

Nitrox just makes it more likely that gas supply will be the limiting factor.

 

[Rick Murchison]

OK folks, I'm looking for an analogy here.
Trying to explain the philosophy of how nitrox increases bottom time..... BUT.......only if you have the gas to use.

Not an analogy, but an example.
I'm assuming she knows how to use the tables... (I'll be using the Navy Tables)
For this example, we can start diving at 8 AM and we have to be done by 6 PM. Our dive site of interest is at 60 feet, and we can get a 30 minute dive out of an 80 at that depth. How much bottom time can we get for the day using air? Using Nitrox? (For simplicity we'll assume an ascent and safety stop time of 5 minutes on each dive - 2 minutes to ascend from 60 feet at 30FPM and a 3 minute safety stop).
So... first, let's look at the air dives.
First dive you're out of the water at 8:35. Your repetitive group is F.
In order to do another 30 minute dive to 60 feet, you have to make it back to group C, so the minimum surface interval is 2:29... so we can get back in the water at 11:04, and get out at 11:39, and our new group designator is H.
We still need to get back to C for another 30 minute dive, so now we need to stay out of the water for 3:21, and we can start a third dive at 3:00 PM. We'll get out of the water from the third dive at 3:35PM... so we have 2:25 left before six; the best we can do is to take a two hour surface interval and make our last dive as an E diver with a bottom time of 20 minutes, out of the water at 6 PM.
Total bottom time on air - 1:50 in four dives.
Now, a look at using Nitrox... (EAN32)
First dive out at 8:35, group E
The tables say I can be an E diver and still make a 30 minute dive to 60 feet on EAN32, but I'll still take the recommended minimum hour surface interval and re-enter the water as a D diver at 9:35, out at 10:10, as an H diver, and I'll need a SI of 1:42 to get back to E for another dive - so, back in the water at 11:52 for the third dive and out at 12:27, as an I diver. Now I need 2:03 SI, so I'm back in at 2:30 PM and out at 3:05, I again, 2:03 SI again, so back in at 5:08 and out and done for the day at 5:43.
Total bottom time on Nitrox - 2:30 in 5 dives.
Rick

 

[The Kraken]

It'd be good to know how old your daughter is.

But anyway.

1: Explain to her the fact the the lungs are going to require the same amount of gas for each breath taken at a given depth. Use a gallon milk jug as an example.
OK, I have a gallon milk jug. How much milk does it take to fill it? answer - 1 gallon
OK, I have a gallon milk jug. How much water does it take to fill it? answer - 1 gallon, DUH!!!

Use this example to show her that just because the mixes of the liquid are different, milk versus water, it takes the same volume of fluid to fill the jug (lungs).

2: Using the RDP (dive tables) ask her to tell you how much time you can do a dive at 100 feet and then how long you can do a dive at 80 feet; answer - 20 minutes and 30 minutes.

3: Now, using an EAD chart or doing the conversion for a breathing gas of EAN32, show her how, by using EAN32, at 100 feet her equivalent air depth is 80 feet (81', but for instructional purposes only, 80 will suffice).

Then explain that by reducing the amount of nitrogen in the breathing gas you are effectively changing the depth of the dive, not really but ya are; because you have less nitrogen in the gas the body won't absorb as much so the body thinks it's at a shallower depth.

But the first step, in my opinion, is the most important because, for some reason, people new to nitrox seem to think that nitrox causes them to have to breathe less.

the K

 

[mksmith713]

IMHO, unless she's going to do many dives in a day, stick with regular air.
As a beginner, she's going to burn through tanks much faster than someone who's been diving awhile so her Max bottom time probably won't even be an issue.
She never get near it.
I'm a pretty husky guy and I still haven't perfected my breathing so I burn an 80 in 50 minutes or so at 40-50 feet.
It's a life long learning thing.