View Full Version : How long will oxygen last?

02-11-2003, 11:57 AM
Does anyone have a formula to figure out how long an oxygen bottle will last? Variables will be size of tank (M and D), Liter per minute, and pressure remaining.


02-11-2003, 12:07 PM
There is one other variable that you did not take into acount. The pearson that is sucking down the oxygen. Some people can go through a 30 minute bottle in 10 minutes if they are working hard while others can make it last longer then 30 minutes.

02-11-2003, 12:18 PM
Well, according to my trusty Praxair Catalog the typical cylinders hold as follows:

D 413L
E 688L
M about 4280L

Cylinders are filled to 2000psi.

Should be all of the information you need to approximate the time to empty a cylinder.

02-11-2003, 01:06 PM
Airborne, this is for medical oxygen, not SCBA air.

OK, 4280L filled to 2000psi. that still doesn't tell me much.

02-11-2003, 01:15 PM
I have heard 1 minute per liter.

02-11-2003, 01:18 PM
OK, here's a scenerio. An M bottle with 400 lbs. pressure and the patient is on 15L NR.

Does this mean it will last 400 minutes?

02-11-2003, 01:24 PM

Probably not. That is what one of my instructors told us many, many moons ago. Each tank will be different and there is no way you will ever know how much each tank will last. Because you never have one tank for NRB's, one for NC, one set at 2 lpm, one set at 4 lpm, etc. That is the only true way you will know how long a tank will last.

02-11-2003, 01:57 PM
I believe that it is listed in one of the brady EMT manuals. I do not have one in the station I was detailed to today. :rolleyes:
I will attempt to find it this evening and post it. I also believe that it only had averages for D cylinders and if they are full. If I remember right at 15Lpm a D size tank will only last around 15-20 mins. I also teach new medics that if they are working a arrest and they have drained a tank and minus any uncanny operating conditions, they have been on scene too long.
IACOJ Bureau of EMS Chairman

02-11-2003, 02:25 PM
Originally posted by machoby
Airborne, this is for medical oxygen, not SCBA air.

OK, 4280L filled to 2000psi. that still doesn't tell me much.

Sorry I was confussed on the question should have looked to see what forum this was in. Please excusse my newbieness.

02-11-2003, 02:26 PM
According to my handy O2 Tank calculator (available for free from various palm software sites), your scenario with the M Cylinder will provide another 36 minutes of oxygen.

The only other way I know of determining how much O2 is left is by using this formula:

(capacity (in L) / service pressure (in psi)) X gauge pressure (in psi) / LPM

In other words, your scenario would include the capacity for an M cylinder divided by the amount of pressure the tank would normally be filled with. Multiply that number by the actual tank pressure as read on the guage (in this case 400) and then divide that number by the LPM you intend to use (in this case 15).

The O2 Tank calculator has the numbers for the different cylinder sizes already programmed into it, so I don't know if it uses the same formula as above or not.

02-11-2003, 08:04 PM
Well....lets say you have 1200 psi left in an M tank at 8 lpm..the equation I would use as far as I remember is:

amount left in tank(L)/2000 psi multiplied by tank size(L)/LPM

ie. 1200/2000*3200/8

02-11-2003, 08:41 PM
How long will oxygen last......

Take a deep breath and hold it.. When you get all freaky-faced and pass out from hypoxia... You oxygen has run out... :D :p :rolleyes:

02-12-2003, 12:35 AM
Thanks for all the responses! That answered my question.

02-12-2003, 08:16 AM
D cylinder = 360L @ 2000 psi
E cylinder = 420L @ 2000 psi
M cylinder = 3000L @ 2000 psi

Divide total amount of litres by 2000 (resulting in a coefficient), multiple coefficient by current pressure in psi, then divide this product by litre/minute flowrate (i.e., D cylinder 360 L/2000 psi = 0.18 x 800 psi(current psi)= 144 L(remaining litres of O2)/15 (L/min via NRB)= 9.6 minutes of available O2.

The coefficinet for the the various tanks are:

D cylinder = 0.18
E cylinder = 0.21
M cylinder = 1.5

A quick method is to divide the pressure remaining in the tank by quarters (500 (1/4), 1000 (1/2), 1500 (3/4), 2000 (1)psi). Divide the maximum tank capacity by 4 and multiple the quarter pressure of the tank (i.e., E cylinder @ 1200 psi is equal to 210 L. Divide by 4 L/min = 52.5 minutes of O2). Enjoy.

02-12-2003, 08:43 AM
:eek: See, even I learn something every day!!! Good Job guys!!

02-16-2003, 09:42 AM
Simple Formula:
Gauge pressure in PSI minus the safe residual pressure (200psi), times the constant (see list), divided by the lpm, equals the duration of flow in minutes.
Cylinder Formula:
D=0.16 / E=0.28 / M=1.56 / G=2.41 / H=3.14
Determine the life of an "D" tank has a pressure of 2000psi displayed on the pressure gauge, and is utilizing a flow rate of 10 lpm.
(2000 - 200) x .16 288
------------------ = ----- = 28.8 minutes
10 10

Hope this helps it was in our EMT class