How Long Does an Oxygen Cylinder Last? ~ Will It Last an Hour? Oxygen Cylinder Math Made Easy ~

2025年9月18日2025年9月24日

You see oxygen cylinders almost every day if you work in the ER, OR, or ICU. Those black cylinders in Japan? Well, in the U.S. and Europe they are usually green or white.

Color codes differ from country to country—so never rely only on color! In the U.S., oxygen is green, while CO₂ may be gray or black.

Contents

♦️Cylinder Sizes and Units

In Japan, we often talk about cylinder volume (e.g., 3.4 L).

In the U.S. and many other countries, cylinders are usually described by letter size:

E-cylinder: ~680 L when full (commonly used for transport)
D-cylinder: ~350 L
H/K-cylinder: ~6,900 L (large stationary cylinders)

Also, note the unit:

Japan uses MPa (megapascal).
The U.S. uses psi (pounds per square inch).
A full E-cylinder is about 2000 psi ≈ 13.8 MPa.

♦️ The Key Formula

The principle is the same everywhere:

Oxygen remaining (L) = Cylinder factor × Pressure (psi)

For an E-cylinder, the cylinder factor is about 0.28 L/psi.
For a D-cylinder, it’s about 0.16 L/psi.

👉 Example: An E-cylinder at 1000 psi:

1000 × 0.28 = 280 L remaining.

♦️ Estimating Duration

Once you know the remaining oxygen, it’s simple:

Duration (min) = Remaining volume (L) ÷ Flow rate (L/min) × 0.8

The 0.8 factor is a safety margin, since flow is not perfectly stable and you don’t want to run completely empty.

👉 Example:

E-cylinder at 1000 psi → 280 L
Flow at 5 L/min
280 ÷ 5 × 0.8 = 45 minutes

♦️ Rules of Thumb

A full E-cylinder (~2000 psi) lasts about 3–4 hours at 2 L/min, or 1 hour at 6 L/min.
If the gauge reads half (1000 psi), you’ve got about half the time.
Quick mental math is totally fine, as long as you understand the principles.