Supplementing oxygen through the oxygen cylinder either to thrive in extreme altitudes (>8,000 meters) to ascent peak or to treat hypoxia related illnesses is a very common practice. This has been in practice since decades. But, every time someone decides to use the oxygen cylinder, s/he faces the most difficult questions;

*How much oxygen is there in the cylinder? And,**How long will it last?*

__Cylinder size and total oxygen capacity:__

The oxygen capacity of the cylinder depends on the size of the cylinder and here is the common type of cylinder size and its capacity:

Cylinder size | D | E | F | G | J |

Oxygen capacity (Liters) | 340 | 680 | 1360 | 3400 | 6800 |

Water capacity (Liters) | 2.3L | 4.7L | 17L | 39L | 47.2L |

To calculate the oxygen capacity of any type of oxygen cylinder the formula is:

`Cylinder Capacity (Liters) = Water capacity × 144`

__Longevity of the cylinder/Duration of oxygen supply:__

This depends on the flow rate, cylinder (tank) pressure, residual pressure and conversion factor of different cylinder size. And, this can be calculated using the following formula:

** Time to runout a cylinder = (Cylinder pressure in PSI – 200) × Cylinder conversion factor** ÷

*Flow rate (Liter/min)***Residual pressure** = 200 (constant)

**Cylinder pressure** = measured in the pressure gauze attached to the cylinder

**Flow rate** = desired flow rate adjusted in the flow meter

Cylinder size | Cylinder conversion factor |

C | 0.085 |

D | 0.17 |

E | 0.34 |

F | 0.68 |

G | 1.7 |

J | 3.4 |

**Cylinder conversion factor** = depends on size of cylinder

__Example:__

Please calculate the time to rundown the oxygen cylinder (F-size) at given pressure and flow rate:

**Gauze pressure** = 2,000 psi

**Residual pressure** = 200 psi

**Flow rate** = 5 liter/min

Time duration = (2000-200) × 0.68 ÷ 5

= 244.8 minutes or 4.08 hours

*Safely used the oxygen delivery devices!*

*Dr. Santosh Baniya, MD (July, 2022)*