MOD markings and Stages

[jjones9527]

Last weekend on a dive I noticed that a regular team mate of ours had changed the MOD markings on his stage bottles (32%) from 120' to 100'. Curious about where he got the idea, we were told that he saw the stickers on the EE website, and phoned them to ask what the deal was. The thought was that a bottle being used as a bottom stage should have a bottom gas MOD (ie 1.2ATA), not a 1.6ATA. So a stage of 21/35 used as a bottom gas would be labeled 150', where as a deco bottle of 21/35 would be labled 190.

Up to this point we have always labeled our bottles with the 1.6ATA MOD, as that is the safe Maximum Operating Depth. I don't quite see the point in separate MOD labels based on the use as a bottom gas or deco gas. So I'm just curious what you all think. Does having separate MOD lables based on use for the same gas make sense to you?

 

[PerroneFord]

I saw this at the WKPP but I didn't think that would translate over. Interesting.

 

[amascuba]

The 120 bottle always confused me anyways because of the variety of mixes it could contain, whether it was 32%, 30/30, or 35/25. I label my 32% stage with a 100' label. I don't understand why they would change the 190 bottle though since it could be used as a stage or as a deco bottle or deeper dives.

The 190 bottle would also be a 1.4 MOD. The 120 bottle would depend on the mix. At 32% the it would be 1.48, 30/30 it would be 1.39, and for 35/25 it would be 1.62. Although putting 32% in a bottle labeled 120 also would violate your 100ft END. For that reason, my 32% stage is labeled 100.

 

[jjones9527]

I don't see the confusion with the 120 bottle. I am only going to have one of those gasses on me for a given dive, and with proper analysis, I know which one it is. I will give you the END for the 32%, which seems like the only one that may need consideration for changing.

 

[amascuba]

Somebody could possibly use a 120 bottle, containing 35/25, on the working portion of a dive at the MOD, increasing the risk of toxing. -- That's the worst case scenario though.

 

[cmalinowski]

Last weekend on a dive I noticed that a regular team mate of ours had changed the MOD markings on his stage bottles (32%) from 120' to 100'. Curious about where he got the idea, we were told that he saw the stickers on the EE website, and phoned them to ask what the deal was. The thought was that a bottle being used as a bottom stage should have a bottom gas MOD (ie 1.2ATA), not a 1.6ATA. So a stage of 21/35 used as a bottom gas would be labeled 150', where as a deco bottle of 21/35 would be labled 190.

Up to this point we have always labeled our bottles with the 1.6ATA MOD, as that is the safe Maximum Operating Depth. I don't quite see the point in separate MOD labels based on the use as a bottom gas or deco gas. So I'm just curious what you all think. Does having separate MOD lables based on use for the same gas make sense to you?

Interesting. Never thought about it. But since we put MODs on our bottles to indicate a max depth at which we think that bottle should be used fearing a tox, not necessarily a 1.6MOD, then it makes sense.

That's the worst case scenario though.

That's the one that usually kills you.

Chris

 

[dsteding]

I recently rigged up some 80s as stages for a variety of uses. But, they were going to only have nitrox in them at this point (32%). After thinking through it, I put 100 foot MOD stickers on, reason being that is the narcotic MOD of 32%.

I suppose this will get clarified with further training, but it seems like a bit of a choice between the few things that drive MOD selection, namely a combination of END, and different PPO2s for different parts of the dive (1.2/1.4/1.6).

 

[lamont]

Somebody could possibly use a 120 bottle, containing 35/25, on the working portion of a dive at the MOD, increasing the risk of toxing. -- That's the worst case scenario though.

There should be a gas analysis sticker with "35.x/25.x" on it.

 

[Warren_L]

If you marked all your bottles with a MOD based on ppO2 1.6 ATA, even stages meant for the working portion of your dive, is there not a benefit of knowing quickly that in an emergency, you could switch to that gas if needed sooner?

 

[jjones9527]

WRT using a 35/25 for a working portion, I would consider that a screw up in the handling of the gas before the dive even started. As was stated the analysis sticker (as well as analysis before the dive), would tell you that you do not have a bottom gas, but a deco gas. I'm becoming convinced of labeling 32% bottles for 100' due to the narcotic potential, which could be justified as the MOD, but for everything else, I think the PPO2 MOD is a better indicator of the safe depth.