Which cylinder factor is used in the duration calculation for H-tanks?

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The main idea is converting pressure into usable gas volume with a cylinder factor, then using that to estimate how long the gas will last at a given flow. The cylinder factor is a fixed value that represents how many liters of oxygen are available per psi of pressure for that specific cylinder size.

For H-tanks, that factor is 3.14. This means roughly 3.14 liters of oxygen are available per psi of pressure in an H-cylinder. At a typical full pressure (for calculation) like 2000 psi, you’d have about 3.14 × 2000 ≈ 6,280 liters of oxygen, and the duration at a given flow is that total liters divided by the flow rate. That’s why 3.14 is used for H-tanks.

Other values aren’t used for H-tanks because they correspond to different cylinder sizes (for example, 0.28 is the factor for smaller E-tanks), and they wouldn’t accurately convert pressure to available liters for an H-cylinder.