Standard MOD

[DaleC]

Spurious argument. EAN50 deco bottles are not <only> filled with EAN50. Many divers only have a few deco bottles and might fill them with O2 & relabel them on occasion. Permanently (which is a bit of a misnomer since the labels are easily scraped off) marking deco bottles but not marking bottom stages is a double standard.

A fill station operator should not be letting mismarked bottom stages out of the shop. e.g. 25/25 in a "220ft" bottle etc. This mismatch should be caught again during analysis by the user, again by the deckhand passing a cylinder to a diver, and once again by the buddy as they drop. 3+ layers for multiple people to say "STOP this is wrong."

Vs. 2 unmarked bottom cylinders which can go from fill station, to truck, to boat, and only get mixed up at the last possible moment when the deckhand passes the wrong one to a diver. Now the diver's hustling to drop and its too late to halt the trainwreck.

I don't know about spurious but I am giving your reasoning due consideration.

To me it breaks down to what one is relying on the MOD stickers for. If one is using them for logistical/organizational reasons I can see the validity of marking all bottles - it avoids potential mix ups.
If one is using them for safety reasons I can see the potential for BG MOD's to be either neutral (no benefit) or even detrimental (in the case of miss labeled MOD's).

Having a FO catch the mismatch would certainly be good but that precludes sloppy FO's and those who fill their own bottles.

Having the user catch the mix up during analysis could also happen (competency catches all the errors with this issue IMO) but I think my greater concern would be those who become somewhat complacent because they move between gasses so much without incident and they think they can "afford" not to switch their mailbox letter MOD stickers "this time" (like cave divers who can afford to leave the line "just this once"). To me, that is where the greatest chance of error would occur.

I guess I also have to wonder what the deckhand on the boat (and the diver receiving) is looking at when handing off bottles. Is it the MOD marking or the divers ID?

There is a chance for either safeguarding or error all along the chain from FO, to analyser, to deckhand, to buddy, to user. Ultimately it's up to the diver to ensure they have the right tanks and the right mix so I guess I wonder what they would look at to ensure this - the MOD or the diver ID.

Case in point: one could inadvertently clip off a bottom stage that isn't ones own but is marked with a MOD; yet how would you know for sure the MOD is correct if you haven't analysed the mix yourself. I don't dive mixes (other than air) I haven't analysed personally. Relying on the MOD could lead to a sense of false security. The MOD is generic but the divers ID and the analysis sticker is specific.

To me, the MOD is there to tell everyone to check their depth because the gas within could be harmful at some portion of the dive; but I also understand that other divers use the MOD for logistical reasons as well.

This discussion also illustrates to me one of the potential negative consequences of standardization. When everyone's bottles look identical there is a chance of mixing them up. Even the MOD's look the same. This is compensated for by putting the divers name/initials on the bottles yet the failure point still seems to be someone not looking at the ID. Is the solution to vary the look of the bottles between divers or to develop a strategy to safeguard against mixing them up. Would the successful strategy be looking at the generic MOD's or looking at the specific diver ID.

 

[Mayor]

Is it really that much extra work that is needed to label everything? Seems like labeling makes things EASIER, because it prevents the need to constantly reanalyze.

Every bottle must be checked the day of the dive to make sure you have the right mix. This is a great habit to get into now so it becomes second nature.

 

[PfcAJ]

I'm going to reply to a number of posts, but I can't multi quote from my phone. Sorry

Dir evolved from a group of divers exploring Sullivans sink, one of the northern most sinks in the Leon Sinks cave system. By implimenting standards, they were able to get more done per dive. Flash forward, and you have the WKPP. In the early days, the standards were much different. Tanks had colored bands to indicate MOD (you can still see the remenants of this practice in a few photos), air was breathed to 190, bottom gas was different, there were more that I don't need to list. DIR was designed for and evolved out of big cave dives, it just happens to work exceptionally well everywhere else, too. 'DIR lite' isn't really DIR.

To reap the benefits of the system, you don't have to be doing big ones at all. The same basic tenents hold across all forms of diving (more or less). Cutting corners only serves to throw a wrench in my mix somewhere else.

We need to discuss why MOD is used on tanks at all. Analysis tape is hard to read underwater, requires math (however simple), comes off easily, and can't be checked by your buddy. MOD, on the other hand, has none of these problems. Any discrepancy between analyzed gas and MOD is corrected on the surface (at the fill station), free from narcosis, cold, dark, or time constraints. If the bottle doesn't have the right gas, it doesn't get a reg. Period. If it doesn't have a reg, its not going in the water. This diligence on the surface prevents a potentially deadly situation under water. The MOD has the same validity as the analysis tape after the bottle is filled, analyzed, and checked prior to the dive. Once again, if I put a reg on it, its the right gas in the right tank, and its clear to everyone; you, your buddy, the deckhand, support divers, surface support, etc. There is no potential of getting 32% when you expected 18/45. If you want to check the tape, go for it, but name and MOD are the identifying factors underwater.

Not marking stage bottles forces at least one person in the team to "assume". AGs letter even admits that blank stages are assumed to be appropriate bottom gas. Really? Assumed? At depth? With MOD markings, there is no assumption. We BOTH know its 300 gas, or 190, or whatever. Why? It was filled and checked at the surface.

 

[limeyx]

I'm going to reply to a number of posts, but I can't multi quote from my phone. Sorry

Without necessarily agreeing or disagreeing on the marking issue, how would you imagine the following working...

You have a 190 deco gas (21/35) Now you want a bottom stage suitable for 150-160 feet?

what do you do ? mark the 21/35 stage at its "MOD" of 190 and somehow you know not to use it as a bottom stage at 1.4 PPO2 ? use some other gas for the 150 stage ? What, and how do you mark it ?

Use 21/35 for the 150 bottom stage and mark it at 150 or 160 MOD (introducing another MOD) so now you have the same gas with 2 different markings ?

What if you want to establish all bottom gas has max PPO2 of 1.0 or even 0.7 for a really long dive where you want your PPO2s low on the bottom --- do you now have to introduce new MODs for all those bottom gases ? What PPO2 do you consider those MODs?

Are you (one) really going to do the math to calculate given the MOD, at what depth each stage is a 0.7 PPO2 based on a 1.4 marking ?

I have a buddy who had GUE training many years ago and from my understanding it was NOT back then policy to mark bottoms stages (in the ocean for sure) and I think AG said that stages were NOT marked on Brittanic and look who was present on that trip ....

I am not sure it's all so black and white....

 

[DaleC]

edit* Nick, you posted while I was typing so some of this is redundant.

Just some points that stand out for me:

Why not white duct tape and a sharpie for analysis tape? It is fine for marking MOD's apparently, easy to read and won't come off easily.

If everybody on the boat is competent enough to mentally deduce multiple mixes from the MOD markings alone, who's the guy not competent enough to hand a diver the right bottle?
Again, all the due dilligence performed by a diver pre dive can be undone if he clips on someone elses tanks (how do you know they also exercised the same care). How will having a stage MOD marked eliminate this error; I don't see it. You could clip on all the right MOD's that way but the bottles could all belong to someone else. One could say it doesn't matter because in a team all the mixes are the same but it would be an interesting poll indeed to ask who is willing to dive tanks of mixed gasses they themselves have not personally analysed.

The MOD doesn't always identify the same mix for everyone. It only describes the MOD. Some people use 1.2, 1.4, 1.6 to calculate MOD and even vary those ata's depending on whether it is to be used for deco or at depth. How does one determine the variables being used (and thus the mix) to calculate the MOD listed simply from the MOD marking alone? Of course the answer is standardization and agreement amongst the team as to mixes used but then... that same arguement can be used to determine that unmarked MOD's indicate stages or BG. It seems that determining the mix by the MOD alone assumes more than the fact that an unmarked bottle indicates breathable gas at any stage in the dive (if that's what ones agency goes by).

DIR proscribes low END mixes to avoid narcossis but one is relying on MOD markings because it will be to confusing to breath an unmarked bottle at depth? And what math is being performed (no calculation is needed if it is agreed that unmarked stages are good to breath throughout the dive). Couldn't one also argue that it is less confusing to have a stage stand out by not being marked with a MOD as being gas one need not check their depth against immediately. For example here are two scenarios:

One is low on air and swims up to a bottle, see's there is no MOD and knows it is good to breath.

One is low on air and swims up to a bottle, see's there is a MOD and has to determine if it is safe to breath.

Anyways, a good discussion so far, I can see valid points on both sides of the issue.

 

[Gombessa]

All I know is, I've tried, and cannot really get a good read on the analysis tape of any of my buddies' stages, especially if there's any kind of chop at the surface, and that means I can't verify his MOD.

Maybe some think it's a little silly when all we're diving is a single stage and no deco gas, but I seem to recall even AG said, "single stages we don't mark MOD, multiple stages we do." If that's the case, I don't see any real downsides if one opts to mark.

 

[LiteHedded]

Without necessarily agreeing or disagreeing on the marking issue, how would you imagine the following working...

You have a 190 deco gas (21/35) Now you want a bottom stage suitable for 150-160 feet?

what do you do ? mark the 21/35 stage at its "MOD" of 190 and somehow you know not to use it as a bottom stage at 1.4 PPO2 ? use some other gas for the 150 stage ? What, and how do you mark it ?

Use 21/35 for the 150 bottom stage and mark it at 150 or 160 MOD (introducing another MOD) so now you have the same gas with 2 different markings ?

What if you want to establish all bottom gas has max PPO2 of 1.0 or even 0.7 for a really long dive where you want your PPO2s low on the bottom --- do you now have to introduce new MODs for all those bottom gases ? What PPO2 do you consider those MODs?

Are you (one) really going to do the math to calculate given the MOD, at what depth each stage is a 0.7 PPO2 based on a 1.4 marking ?

I have a buddy who had GUE training many years ago and from my understanding it was NOT back then policy to mark bottoms stages (in the ocean for sure) and I think AG said that stages were NOT marked on Brittanic and look who was present on that trip ....

I am not sure it's all so black and white....

AG did say stages were not marked on the brittanic.
although aj posted a screenshot of him using a 400 bottle that was clearly marked.
AG says lots of things...

 

[PfcAJ]

I think it comes down to taking the right gas in the right tank with the right marking.

If you're MOD for said dive is 150, then put a 5 over the 9 and go.

I'm quite the fan of 150, 200, 250 and 300 markings, but Ill dive 190 and 240 markings all day long. Rjack mentioned earlier about bottom MODs being a bit flexible, and I agree 100%.

And AG saying something doesn't make it correct, esp when the video footage suggests otherwise. Also, back then, many things were different. I'm sure no ones suggesting color coding tanks anymore, either.

Dalec, we use standard gases for certain depth ranges and certain markings. If ithe plan calls for show ing up with 190 gas, were all going to have 18/45. That's the beauty of having a truly standardized system. Having your stage unmarked means no one can easily and readily tell what's in there. The info is scrawled on a piece of tape somewhere. I cannot fathom that being superior to big, bold markings that everyone can see.

Also, if no math is needed, then what exactly are you checking on the analysis tape? Your scribbled initials? That's a good way to do the funky chicken at 200ft.

I've accidentally clipped off someone elses tank before. The big Richardson sticker tipped me off, and we just traded back

What's really going on here is utd has too many gasses for each depth, and can't realistically mark them all. "Utd/dir long duration ppo2 of .7" and I think 1.0 for regular...double for each depth range? I have 3 stage markings on my tank fleet: 100, 190, and 300. Done. If I did more at the 150 range, id own a few of those, too.

 

[lamont]

What's really going on here is utd has too many gasses for each depth, and can't realistically mark them all. "Utd/dir long duration ppo2 of .7" and I think 1.0 for regular...double for each depth range?

+1 confused

has UTD gone to multiple different ppO2 MODs based on duration?

 

[PfcAJ]

Yea, point 8 from AGs post that was linked earlier. Pretty interesting, to say the least...

I made an error above, though. Its 0.7 for long duration and 1.2 for short, apparently. I apologize for any (additional) confusion.