D cylinders contains 350 liters of oxygen
E cylinders contains 625 liters of oxygen
M cylinders contains 3,000 liters of oxygen
The safe residual pressure is usually considered 200 psi. (Agencies have different protocol. Medical director can change). Safe residual pressure means that is an acceptable pressure left over in the tank for turning it in and switching out for a new tank.
Each cylinder size has its own CONSTANT:
D cylinder's constant is 0.16
E cylinder's constant is 0.28
M cylinder's constant is 1.56
The following formula for determining how many minutes left in a tank at a specific flow rate......
(PSI in tank - 200) x CONSTANT
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Flow rate in L/min
Example: You are in an ambulance and the house tank (for this example an M tank) has 1000 psi left in it. You are being called to a patient that is on a nasal cannula at 4 L/min. Using the chart you can see the constant for an M tank is 1.56. You now have all the information you need. 1000 (psi in tank) minus 200 (safe residual pressure) is 800. 800 multiplied by 1.56 (constant for M tank) is 1248. 1248 divide by 4 (patient's flow rate in L/min) is 312. You have approximately 312 minutes to run your O2 at a flow rate of 4 L/min.