Ladygodiver
Registered
What is the formula for calculating my personal breathing rate (PBR) ??
Personal Breathing Rate
- Thread starter Ladygodiver
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
Hi Ladygodiver,
Hi
Well, an easy way to calculate breathing rate will be; sit at 33ft of salt water (or 34ft in fresh water), and breathe for 10 minutes. Look at how many psi you've gone through ( 500psi in the 10 minutes, as an example) then your breathing rate at 33ft of salt water is 50psi per minute. The absolute pressure at 33ft is 2 atmospheres, so your breathing rate at the surface will be half of that. Now there is one more things you should consider, what size tank are you using? (For recreational diving the most common tank is 80 cubic feet and is pressurized to 3000psi) so let's say that that's the tank you're using. After spending your 10 minutes at 33ft (it's just more fun to do it in the water, then sitting on the surface breathing from your reg), you've found out your surface air consumption rate (SAC rate), you then can find out how many psi you'll be breathing at any given depth. You just have to know what will be the absolute pressure at the depth you're going to. Remember that at 33' you are at 2 ata, at 66' you are at 3ata, 99' 4ata. But another way to calculate the atmospheric pressure at a curtain depth will be depthx33 divide by 33 (in fresh water use 34), and then do your SAC rate times the absolute pressure. It's a good thing to also know how many cubic feet of air you breath per minute, because you may be using different size tanks for your dives. By knowing how many psi you breathe per minute with an 80 CF tank with maximum pressure of 3000psi, you can easily calculate your consumption rate in cubic feet as well.
I always hope that more divers will know their SAC rate and not forget to add it to their dive plan, this is just as important as knowing what depth you're planning on going to and how long the dive is planned for.
Pinny
http://www.worlddivingzone.com
Hi
Well, an easy way to calculate breathing rate will be; sit at 33ft of salt water (or 34ft in fresh water), and breathe for 10 minutes. Look at how many psi you've gone through ( 500psi in the 10 minutes, as an example) then your breathing rate at 33ft of salt water is 50psi per minute. The absolute pressure at 33ft is 2 atmospheres, so your breathing rate at the surface will be half of that. Now there is one more things you should consider, what size tank are you using? (For recreational diving the most common tank is 80 cubic feet and is pressurized to 3000psi) so let's say that that's the tank you're using. After spending your 10 minutes at 33ft (it's just more fun to do it in the water, then sitting on the surface breathing from your reg), you've found out your surface air consumption rate (SAC rate), you then can find out how many psi you'll be breathing at any given depth. You just have to know what will be the absolute pressure at the depth you're going to. Remember that at 33' you are at 2 ata, at 66' you are at 3ata, 99' 4ata. But another way to calculate the atmospheric pressure at a curtain depth will be depthx33 divide by 33 (in fresh water use 34), and then do your SAC rate times the absolute pressure. It's a good thing to also know how many cubic feet of air you breath per minute, because you may be using different size tanks for your dives. By knowing how many psi you breathe per minute with an 80 CF tank with maximum pressure of 3000psi, you can easily calculate your consumption rate in cubic feet as well.
I always hope that more divers will know their SAC rate and not forget to add it to their dive plan, this is just as important as knowing what depth you're planning on going to and how long the dive is planned for.
Pinny
http://www.worlddivingzone.com
If you go to this page:
Click Here
...you'll find various calculators for figuring out tank volume, surface air consumption, etc.
[Edited by King_Neptune on 08-31-2000 at 12:44 PM]
Click Here
...you'll find various calculators for figuring out tank volume, surface air consumption, etc.
[Edited by King_Neptune on 08-31-2000 at 12:44 PM]
As "Pinny" mentioned, your air consumption should be in cubic feet (or liters) per minute and NOT PSI per minute because PSI is inaccurate. For example you can breathe 200 PSI in a pony bottle in a couple minutes while it would take you 5xs longer to breathe 200 PSI in an 80 cf cylinder.
As a technical diver, I have to know my SAC (Surface Air Consumption) rate to calculate how much gas I will need for a tec dive.
Here is the formula I use:
[[(psi used/working pressure of tank) X total cylinder capacity]/[(depth in feet + 33)/33]]/amount of minutes
In "English..." take your used PSI and divide it by the working tank pressure. Multiply the number you get by the total cylinder capacity and you will get another number, lets call this "X." Next take your depth (in feet) and add 33. Take the number you get and divide it by 33, we will call this number "Y." Next, divide "X" by "Y" and you will get another number called "Z." Divide Z by the amount of minutes and you get your SAC rate!
So say you want to see your SAC rate at depth. At 60 feet (or whatever), level off and record your starting pressure, go along your dive for lets say 5 minutes then record your ending pressure. Subtract these two to get how much PSI you used, "psi used." Next check the working pressure of your tank on the tank stamp, usually it is 3000 "working pressure of tank". "Total cylinder capacity" will be how much cubic feet it holds (ex standard tanks are Aluminum 80s so 80 cubic feet).
As a technical diver, I have to know my SAC (Surface Air Consumption) rate to calculate how much gas I will need for a tec dive.
Here is the formula I use:
[[(psi used/working pressure of tank) X total cylinder capacity]/[(depth in feet + 33)/33]]/amount of minutes
In "English..." take your used PSI and divide it by the working tank pressure. Multiply the number you get by the total cylinder capacity and you will get another number, lets call this "X." Next take your depth (in feet) and add 33. Take the number you get and divide it by 33, we will call this number "Y." Next, divide "X" by "Y" and you will get another number called "Z." Divide Z by the amount of minutes and you get your SAC rate!
So say you want to see your SAC rate at depth. At 60 feet (or whatever), level off and record your starting pressure, go along your dive for lets say 5 minutes then record your ending pressure. Subtract these two to get how much PSI you used, "psi used." Next check the working pressure of your tank on the tank stamp, usually it is 3000 "working pressure of tank". "Total cylinder capacity" will be how much cubic feet it holds (ex standard tanks are Aluminum 80s so 80 cubic feet).
kundalinichi
Registered
- Messages
- 67
- Reaction score
- 10
- # of dives
- 200 - 499
Talk about reviving an old thread.. good explanation though.
whodunit68
Contributor
no kidding, that has to be the oldest one I've seen come back. 12 years...with the tens of thousands of posts on here, how does one even uncover such a thread? Wow.
Back then they were able to answer a question and be done with it!
smokin3000gt
Registered
Good information regardless how old it is. I'm glad it was bumped otherwise I wouldn't have stumbled on it to learn something new. Thanks TP.
I've never heard it referred to as "PBR"... Amongst my dive buddies, someone would surely try to hand you a beer instead of helping you monitor your air consumption 
clownfishsydney
Contributor
Never heard of PBR in 25 years. SAC or Respiratory Minute Volume (RMV) are the accepted terms. In all but the USA, it is measured in litres per minute.
Similar threads
