Standard vs Metric

[debajo agua]

As I understand it, outside of America, other countries deal in units of psi called BARs, and of course, meters. When diving abroad, do most foreign countries deal in metric, which would leave Americans converting numbers, or does the dangerous nature of scuba diving convince manufactures to produce products in a universal system of measurement (e.g. if I travel to Greece and rent a tank, will the tank pressure gauge measures pressure in bars) ?

TIA

 

[tyesai]

The equipment I've seen in Turkey and Spain has all been metric so yes you would have to do the conversions but it isn't hard.

I'm an American living in Spain and my pressure gauge is in psi, and I have my computer set to meters. The pressure gauge has caused others some confusion so I marked it in grease pencil 200 / 100 / 50 which in bars is full, 1/2 full, and time to come up. I could buy another, they aren't that expensive, but I'm not going to be here forever and the grease pencil takes away the confusion.

 

[oreocookie]

If you're renting gear, whether you're going to get metric gauges (meters/bar) or psi/feet (I don't like your use of "standard", btw, but i digress) depends on where you go. For example, Europe probably uses metric most commonly, but psi/feet is probably not impossible to find. The Caribbean seems to go mainly with psi/feet even though a lot of those countries probably use metric for most other things. If you come to Canada, you'll probably get psi/feet but I have rented metric gauges by accident.

If you're going to be renting, find out ahead of time what system they use and take a few minutes to familiarize yourself with it if you need to. If you're not renting (or even if you are) and aren't sure about the number a DM gives you (eg for the reserve pressure they want), ask them. And don't forget to discuss it with your buddy if they're your not your usual buddy because underwater is not the place to find out they've got metric gauges and you don't (I know from experience that this makes communicating pressure difficult).

 

[melanie.]

In Canada we still use PSI, feet, and fahrenheit for water temp. I have only seen a BAR guage in Cuba.

Interesting point. I was raised with celsius, and that is how I "feel" air, fahrenheit makes no sense to me. But when it comes to water, we have always gone by fahrenheit, so I don't know what water "feels" like in celsius.

 

[Dirty-Dog]

First off, I'd suggest "imperial" rather than "standard". The metric system is used in far more places, and if anything should be considered "standard" it's probably the metric system.

As far as rental gear, I suspect you'll find whatever units of measurement are most commonly used by tourists. In Mexico, for example, the scads of American tourists means you'll have no diffilcuty finding PSI/FT. In someplace where the majority of tourists are European, you'll most likely be looking at BAR/M instead.

One of the good things about owning your own kit is that it makes this a non-issue.

 

[ferris213]

I have dived in a number of countries and never seen an imperial gauge. Like the others have said it just depends where you are.

One thing that is different is the 'back on the boat' pressures. Every boat I have been on wants you to surface with 50bar, which is about 725psi I think. If you were to surface with 35 bar (which is 500psi) you would be well and truly in the red, and could be prevented from diving with them again.

Edit: I have dived in Greece and yes they did use bar/meters.

 

[DiveNav]

Most of the World uses the Metric system.

Here in USA the metric system is used also when dealing with Partial Pressure (You will learn about this if/when you will become Nitrox certified) .... so, here in USA you will fill your tank using the "Imperial" system (PSI), but you will estimate the O2 toxicity in your body using the "Metric" system .... go figure.

Alberto (aka eDiver)

 

[j2s]

The 'Standard' or 'Imperial' is a system we should have left behind years ago !!!......Sometimes I dive w/mixed groups, Europeans and Americans..My gauges have both and I wear two computers, one metric, one 'Imperial' in case of emergencies....It's ridiculus...The metric system is so much easier [our money is metric, base 10 ]..Do calculations/formulas w/both, metric is so much simpler...The British gave us 'Imperial' then switched to metric...We should have long ago....[ Can't figure why the British still drive on the 'wrong side' of the road though :O ]....

 

[Akimbo]

...Here in USA the metric system is used also when dealing with Partial Pressure (You will learn about this if/when you will become Nitrox certified) .... so, here in USA you will fill your tank using the "Imperial" system (PSI), but you will estimate the O2 toxicity in your body using the "Metric" system .... go figure.

Alberto (aka eDiver)

Not sure I understand. Are you talking about Atmospheres? Atmospheres are not strictly a Metric unit. The Metric unit Bar is close to one Atmosphere, but does not equal it.

One Atmosphere equals:
SI/Metric Units

101,325 Pascals
101.325 KPa, Kilo Pascals, or 1000x
0.101325 MPa or Mega Pascals or 1 Million x
1.01325 Bar
10.06275861 Meters of Sea Water*​

Imperial Units

14.69594878 PSI
33.0142999 Feet of Seawater*​

* based on a density of 64.1 Lbs/Ft³

 

[Kevrumbo]

Actually, convert to and stay with metric units. . .it's much easier in figuring out breathing rates and makes more sense!

Using 0.75 cf/min imperial units for a convenient starting/reference Surface Consumption Rate (SCR) --in metric, this is approximately equivalent to 22 litres/min.

The common AL80 Tank holds 11 litres volume at the surface standard of 1 ATA (or 1.01 bar), for a metric rating of 11 litres/bar.

22 [-]litres[/-]/min divided-by 11 [-]litres[/-]/bar equals 2bar/min SCR (Surface Consumption Rate) in pressure units --a more useful quantity to utilize during the dive since your SPG reads in bar pressure units.

Your depth in meters, which converts easily to ATA (simply divide-by-10 and add 1) becomes your multiplier depth factor for your 2bar/min pressure SCR.

Example: 30m depth is 4 ATA; your 2bar/min SCR at depth -or Depth Consumption Rate (DCR)- now becomes 8bar/min. [4 times 2bar/min equals 8bar/min]. So 10 minutes at depth 30m on an AL80 (11L/bar) tank in nominal conditions, you would expect to consume 80bar of gas and your SPG reading to be down or show a delta of 80bar. . .

What if your SCR, or Depth Consumption Rate (DCR) is lower or better than the example above? --Just scale it as a percentage result:

My SCR/RMV in tropical warm waters is typically 30% better than it is in temperate cold SoCal homewaters. However, after a week drift diving in Palau 30deg C water temp, I've lowered that to around 50% of my nominal cold water SCR (from 22 litres/min to 11 litres/min).

This is how I used this value with a 11 litres/bar tank (i.e. an AL80) in Palau:
11 [-]litres[/-]/min divided-by- 11 [-]litres[/-]/bar equals 1 bar/min pressure SCR.

All my dives are averaging 20 meters depth going with the drift current; 20 meters is 3 ATA (divide 20 by 10 and add 1 gives a depth in atmospheres absolute of 3 ATA).

Therefore 1bar/min multiplied by 3 ATA equals a depth consumption rate of 3 bar/min at 20 meters. Checking my bottom timer every 10 minutes, I expect to consume 30 bar (3 bar/min multiplied by 10min equals 30 bar), and accordingly my SPG should read 30 bar less in that 10 minute time frame.

So by 30 minutes elapsed dive time at 20 meters, I expect to be down 90 bar or at half tank (AL80 full tank is 200 bar). At 40 minutes elapsed time, I'm ascending off the wall into the shallow coral plateau around 9 meters (down 120 bar from 200 bar total, or 80 bar remaining in tank). And finally at the 45 to 50 minute mark, I'm at 6m and my 3-5min safety stop with 60 to 70 bar left. I surface and I know even before looking at my SPG that I have around 50 bar remaining in my tank.

This is how you should actively use your SCR with your particular tank, knowing how much breathing gas you have left, not just only pre-planning, but also during the actual dive real-time-on-the-fly --all with easier to use metric units . . .additionally, you have a SPG that reads in units of pressure: why not convert your SCR to a Depth Consumption Rate (DCR) in pressure units to make use of it???​