Does Nitrox kill brain cells?

[Cave Bum]

The PADI tables don't really show MOD. What they show is the PPO₂ for various %O₂ at given depths. So the depth that meets but doesn't exceed 1.4 is the MOD.

Well, that in itself is an argument for using the formula, if the table doesn't list MOD, but instead lists some max depth that is 'less then or equal to' the MOD. The last couple of PADI Nitrox courses I've taught I've had the students use the PADI book (a requirement), but I've use the IANDT Powerpoint for the classroom portion. I think it's more accurate and easier to understand. The PADI video, at least the version of it I have, has information in it that's just flat wrong. (Yes, I know, I'm a PADI instructor but that doesn't mean I have to condone bad information. That's part if why I'm switching to IANTD for the more technical subjects...)

If you consistently want to do 1.35 you generate another table I don't know about the other agencies but the formula in PADI's book is a one variable equation (%O₂). So not sure how many people will know how to calculate it as a two variable equation.

I've thought of coming up with a spreadsheet, to give out on the internet, to do just that. I have others that I give away, one for mixing gases, that includes the FO2 and MOD at both 1.4 & 1.6 PO2. After reading the responses in this thread, I've been thinking that maybe a spreadsheet of handy scuba formulas might be of use to some folks...

 

[mikemill]

What will the formula give you? Well, the knowledge to figure your MOD without needing the tables.
Hey, dive how you like. Personally I don't need the EAN tables. I can do the math on the fly... and if need be, in the water.

If you don't trust your analyzer, I don't know what to tell you.

I said I don't trust the analyzer to give me two digits of precision.

Well the formula tells me that the MOD is the depth at which the partial pressure of O₂ is equal to some value (with 1.4 being the magical value). It also tells me that the partial pressure is found by multiplying the total pressure by the percent of O₂. Now the deeper question might be why 1.4 is the magical number.

Well, that in itself is an argument for using the formula, if the table doesn't list MOD, but instead lists some max depth that is 'less then or equal to' the MOD. The last couple of PADI Nitrox courses I've taught I've had the students use the PADI book (a requirement), but I've use the IANDT Powerpoint for the classroom portion. I think it's more accurate and easier to understand. The PADI video, at least the version of it I have, has information in it that's just flat wrong. (Yes, I know, I'm a PADI instructor but that doesn't mean I have to condone bad information. That's part if why I'm switching to IANTD for the more technical subjects...)

Well the table I use is not the PADI table. It is a table that has two sets of columns. The first is the %O₂ and the second is the MOD as calculated using the formula. So I get the best of both worlds

I've thought of coming up with a spreadsheet, to give out on the internet, to do just that. I have others that I give away, one for mixing gases, that includes the FO2 and MOD at both 1.4 & 1.6 PO2. After reading the responses in this thread, I've been thinking that maybe a spreadsheet of handy scuba formulas might be of use to some folks...

Not a big fan of spreadsheets as they aren't very portable between systems (i.e. if you gave me an excel spreadsheet I'd have to hurt you). I did write a PHP page that calculated the MOD for 15% to 100% in 0.1% increments (removing duplicate sequential MODs to reduce table size) and also to give the max %O₂ for depths from 1 to 150ft. (Just take the two variable equation and solve for %O₂ instead of depth).

 

[Captain12Pk]

Not a big fan of spreadsheets as they aren't very portable between systems (i.e. if you gave me an excel spreadsheet I'd have to hurt you). I did write a PHP page that calculated the MOD for 15% to 100% in 0.1% increments (removing duplicate sequential MODs to reduce table size) and also to give the max %O2 for depths from 1 to 150ft. (Just take the two variable equation and solve for %O2 instead of depth).

Isn't a set of tables essentially a spreadsheet? So you'll go through all of this but you won't do some simple math to figure out your MOD after a fill?

 

[Cave Bum]

Not a big fan of spreadsheets as they aren't very portable between systems (i.e. if you gave me an excel spreadsheet I'd have to hurt you). I did write a PHP page that calculated the MOD for 15% to 100% in 0.1% increments (removing duplicate sequential MODs to reduce table size) and also to give the max %O₂ for depths from 1 to 150ft. (Just take the two variable equation and solve for %O₂ instead of depth).

I'll have to look into PHP. I started to do that a few years ago but lost interest and/or got in over my head, I don't remember which... I programmed my web site with Front Page (yes, I'm behind the times, but it's the program I know and it produces usable html code!). I do have some java applets in it...

I originally wrote the Excel Spreadsheet I give on my web site, Bankmixer, for use at the fill station I was working at. Since it's been out there for free download it's had an amazing amount of DL's and a lot of positive comments from folks who use it. They can get the free office suite, OpenOffice, from Sun on the internet rather then having to buy MS Office.

If you have any suggestions on where I can pick up some tips on PHP so I could do a companion page to the spreadsheets I have out there, I'd appreciate the info...

 

[mikemill]

Not a big fan of spreadsheets as they aren't very portable between systems (i.e. if you gave me an excel spreadsheet I'd have to hurt you). I did write a PHP page that calculated the MOD for 15% to 100% in 0.1% increments (removing duplicate sequential MODs to reduce table size) and also to give the max %O2 for depths from 1 to 150ft. (Just take the two variable equation and solve for %O2 instead of depth).

Isn't a set of tables essentially a spreadsheet? So you'll go through all of this but you won't do some simple math to figure out your MOD after a fill?

A spreadsheet is one way of representing it. And "going through all of that" was like 5 mins worth of work

For the 1.4 value my LDS already has the table printed off.

I'll have to look into PHP. I started to do that a few years ago but lost interest and/or got in over my head, I don't remember which... I programmed my web site with Front Page (yes, I'm behind the times, but it's the program I know and it produces usable html code!). I do have some java applets in it...

I originally wrote the Excel Spreadsheet I give on my web site, Bankmixer, for use at the fill station I was working at. Since it's been out there for free download it's had an amazing amount of DL's and a lot of positive comments from folks who use it. They can get the free office suite, OpenOffice, from Sun on the internet rather then having to buy MS Office.

If you have any suggestions on where I can pick up some tips on PHP so I could do a companion page to the spreadsheets I have out there, I'd appreciate the info...

Um not sure the best place to learn it. I just picked it up as an extension to other languages I already knew. I'd be more then happy to convert some of the spreadsheets to PHP if you'd like.

 

[DaleC]

Please enlighten me. How is knowing how to figure out my MOD reinvnting the wheel?

There is knowing how to do it and there is doing it each time.

If you have a set of tables the math has been done. Unless little elves come along in the middle of the night and switch the values, that table will always contain the answer you need to plan the dive. If you want to "recalculate" the values everytime you get a fill that's up to you. There's nothing wrong with doing math puzzles (I like to do crosswords) but it doesn't make you any more intelligent than the person who has figured out that the math has already been done.

Diving Nitrox is not rocket science and the degree of accuracy that some are worried about isn't neccisary. It will not add safety to the dive. The MOD's are just guidelines that do not take into account the individuals reaction to oxygen toxicity. You "opt" for the partial pressure risk you're comfortable with (1.2, 1.4, 1.6 etc...) and go from there. If anyone thinks an OxTox event can be avoided by diving the MOD indicated by a decimal point (31.5% as compared to 32% for example) they are overestimating their ability to manipulate fate.

 

[BHB ScubaTroll]

Now the deeper question might be why 1.4 is the magical number.

At this point I have to ask... Have you not taken an OW class or even a Nitrox course?

The answer was discussed in both. It was when the instructor began talking about partial pressures, how they affect and what effect they have on the body... Including the partial pressure of O2 for when it becomes toxic to the human body (1.6).

 

[Captain12Pk]

There is knowing how to do it and there is doing it each time.

If you have a set of tables the math has been done. Unless little elves come along in the middle of the night and switch the values, that table will always contain the answer you need to plan the dive. If you want to "recalculate" the values everytime you get a fill that's up to you. There's nothing wrong with doing math puzzles (I like to do crosswords) but it doesn't make you any more intelligent than the person who has figured out that the math has already been done.

Diving Nitrox is not rocket science and the degree of accuracy that some are worried about isn't neccisary. It will not add safety to the dive. The MOD's are just guidelines that do not take into account the individuals reaction to oxygen toxicity. You "opt" for the partial pressure risk you're comfortable with (1.2, 1.4, 1.6 etc...) and go from there. If anyone thinks an OxTox event can be avoided by diving the MOD indicated by a decimal point (31.5% as compared to 32% for example) they are overestimating their ability to manipulate fate.

I don't recall saying that one should dive 31.5% as opposed to 32.00%. I haven't suggested any such thing. But I would still like to why you feel that I, by knowing and using the simple math formula to compute my MOD is reinventing the wheel. Please tell me.

 

[mikemill]

At this point I have to ask... Have you not taken an OW class or even a Nitrox course?

The answer was discussed in both. It was when the instructor began talking about partial pressures, how they affect and what effect they have on the body... Including the partial pressure of O2 for when it becomes toxic to the human body (1.6).

I've taken the courses. While we did talk about that it doesn't explain how that particular number came to be the magic number. For example I've seen references to people diving at higher partial pressures in the past. Now like a lot of things it could be that people start off higher and went lower in attempt to be safer. But that doesn't explain how 1.4 was decided as the cut off.

 

[BHB ScubaTroll]

Because tissue loading takes a huge spike at 1.5, and then again at 1.6