Bar vs PSI

[KOMPRESSOR]

Since you all should start using the metric system the sooner the better, I think you should start using BAR at once!

Depending on tank size and the pressure you fill it with, I find most SPGs here in Norway are marked at either 30 or 50 bars. Typically SPGs graded to max 400 bar (for 300 bar usage!) are marked at 50 bars, suitable for the typical 10 litre 300 bar tanks. SPGs graded to max 300 bar (For 200-232 bar usage!) are marked at 30 bar, suitable for the typical 15 litres 200 bar tanks.

Since I use a 12 litre 300 bar tank, none of these markings "suits" my tank, and I couldn't care less since it has no practical usage to me. I know when to get up! That's usually decided by my bottom time. -And I'm never even close to running out of air when I'm on the way up, slowly...

 

[Hank49]

Holy crap, I can't believe I'm reading this. Have you ever heard of gas planning? Even for recreational! Follow the red line where? When you're at 30m or at 3m? Diving an LP72 or a HP120? Solo or with a buddy?

.

Not to mention that SPG springs stretch and after long use can read 50-60 bar even when the tank is about empty.

 

[Aeolus]

My dive computer allows me to switch between psi or bar. I use an Oceanic Data Pro Plus. I would suspect that most other computers do the same thing. I agree that dive planning should take precidence over a specific pressure on your gauge. Everybody is different, thank goodness.

DSDO

 

[donacheson]

Holy crap, I can't believe I'm reading this. Have you ever heard of gas planning? Even for recreational! Follow the red line where? When you're at 30m or at 3m? Diving an LP72 or a HP120? Solo or with a buddy?

The 50bar/500psi are arbitrary figures designed to get new divers out of the water with some air in reserve. They're not hard and fast figures you MUST follow. As figured out by the first poster, they're not even the same amount of air even if used on the same sized tank. On some dives they're excessive, on others woefully inadequate. Do a search on the term "rock bottom" calculations and learn about planning you air usage PROPERLY.

Amazing, isn't it!

However, the circumstance Helipilot found himself in probably had little to do with planning air usage; it likely had more to do with lazy divemasters who are more dedicated to getting out of the water as soon as possible than to ensuring that their customers have an enjoyable dive.

 

[mossym]

it's funny, i think that red zone is aimed at new students on OW classes diving AL80's which i would guess is the vast majority, to give them a visual clue that with an AL80, the depths they are at for their OW class, and the experience they have, that having the needle in that red zone is a bad place to be. Just telling them that 500psi with an al80 is out time might not work

that said, soon as you finish your class, you'll start to ignore it. This whole scenario is a mute point if classes jsut thought proper gas management. Like Roo said, there is no hard limit that applies to all of 1 persons dives, let alone a hard limit for all divers.

 

[aquaoren]

Some SPGs (such as OMS G240) do have both BAR and psi markings. I’m sure that many divers (including myself) find that useful but an equal number of divers may feel that having both BAR and psi on the same gauge is confusing...

Well, I have one of the OMS SPG's in BAR and PSI and it's the least accurate SPG, I've ever seen.
It has 35-50 BAR deviation from my Uwatec SPG (Accuracy confirmed by Uwatec Aladin Air X) and it's brand new.

 

[Dan Gibson]

Here is a neat little conversion found on another list that's not too tough to do underwater:

1 BAR = 14.7 psi or 15 psi

BAR to psi
Add 50% and adjust the decimal point.
140 BAR -> 14+7 = 21 or 2100 psi
220 BAR -> 22+11=33 or 3300 psi

psi to BAR
take 2/3rds of psi and adjust decimal
2700 psi -> 27-9 = 18 or 180 BAR
1400 psi -> 14-5 = 9 or 90 BAR (approximate)

Thanks everyone for the great info.
I guess I should have been a bit clearer with my question. I was wondering why the gauges are marked differently. Is it a function of Bar vs PSI? Or is it just the choice of the gauge manufacturer? I agree that during a dive is not the place to be doing conversions in your head. I have since used a label maker and added some key BAR amounts on the glass.

 

[Hoosier]

It is awesom way. Thanks.

Here is a neat little conversion found on another list that's not too tough to do underwater:

1 BAR = 14.7 psi or 15 psi

BAR to psi
Add 50% and adjust the decimal point.
140 BAR -> 14+7 = 21 or 2100 psi
220 BAR -> 22+11=33 or 3300 psi

psi to BAR
take 2/3rds of psi and adjust decimal
2700 psi -> 27-9 = 18 or 180 BAR
1400 psi -> 14-5 = 9 or 90 BAR (approximate)

 

[KOMPRESSOR]

My dive computer allows me to switch between psi or bar. I use an Oceanic Data Pro Plus. I would suspect that most other computers do the same thing. I agree that dive planning should take precidence over a specific pressure on your gauge. Everybody is different, thank goodness.

DSDO

To be more spesific, most air integrated computers can switch between BAR and PSI. MOST COMPUTERS aren't air integrated!

I prefer a good SPG + a good bottom timer + dive planning + a good sense of what the heck I'm doing right now. Computers are for work and internet and stuff

Thanks for the math further up here. Now I know I fill my 12 Litre tanks to 4850 PSI! Way cool!

 

[Iruka]

I found it quite surprising that the guide/DM would require you to convert/signal in Bar if you have a PSI gauge....most of my (Japanese) divers here in Guam use Bar, but Americans usually have PSI. The only thing I request of my US divers is that they signal me showing ALL the zeroes.....because a diver with PSI signalling "1 0 0" would have me think they have 100 bar....or 1500 psi....1/2 a tank left. If they actually had 1000 psi, it's only 1/3 tank, or about 70 bar. Truthfully, here in the tourist-infested (ha ha) waters of Guam, we get a fair amount of divers who don't think to check their own air pressure.

That reminds me, a few years back, after diving about 30 minutes, I re-checked the air on my divers....one of them...and then her friend as well...gave me a "1 8 0" for 180 bar, which is somewhere around 2500 psi. Even with excellent air consumption, that sounded a little high. Turns out one of them...and then the other...BOTH read their COMPASSES (180 degrees) rather than their SPGs! Anyhow, I'm glad they were facing south at the time...if they had faced north (0 degrees) they might have panicked when they saw they had "empty" tanks!