Oxygen tank duration calculator: will the rider's cylinder last the ride and the wait?

How to use the oxygen duration calculator

Choose the rider’s cylinder size, enter what the gauge reads and the flow setting, then enter the minutes the trip takes. The calculator returns how long the oxygen lasts, the time to spare or the shortfall, and the gauge reading the ride should start with. On a NEMT trip the rider manages their own oxygen (portable oxygen explains who does what), so this is a booking check on whether what the rider has outlasts the ride, the visit and the ride home. The fields open with example numbers, so type over each one.

1. Pick the cylinder size, or choose “Another size” and enter its factor.
2. Enter the gauge reading in psi, read with the valve open just before the ride.
3. Enter the flow setting in liters a minute, as set on the regulator.
4. Leave the reserve at 200 psi, or raise it to match your policy.
5. Enter the ride there, the time at the appointment and the ride home in minutes, plus extra time for delays.
6. Read the oxygen time, the spare time or shortfall, and the starting gauge reading.

What is the formula for how long an oxygen tank lasts?

Take the tank pressure, subtract the reserve, multiply by the cylinder factor, and divide by the flow in liters a minute. The Virginia Department of Health’s oxygen cylinder guidance gives the formula with a 200 psi reserve. The factor is liters of oxygen per psi: the liters a cylinder holds divided by the pressure it is filled to, which is how a Tampa General Hospital handout on cylinder duration defines it.

Virginia lists 0.16 for a D cylinder and 0.28 for an E, and 1.56 and 3.14 for the much larger M and H or K sizes, which you can enter under “Another size”. It has no figure for the small M6 and M9, so the calculator takes those from one maker’s rated liters divided by its fill pressure: 170 liters at 2,216 psi for the M6 and 255 liters at 2,015 psi for the M9.

This table shows how long each size lasts from a gauge reading of 1,800 psi at 2 liters a minute, with 200 psi held back.

An M6 from 1,800 psi runs 62 minutes, less than half the 140 minutes the example trip below spends on the road and at the visit. For a table of full-cylinder times on a long drive and the battery times of portable concentrators, see long-distance NEMT trip rider care.

How much reserve should stay in the cylinder?

Leave at least 200 psi, and more if your own policy says so. Virginia’s formula takes 200 psi off the reading before it multiplies. Intermountain Health’s patient sheet for home oxygen is stricter: change the cylinder before the needle falls below 500 psi, and replace one with less than 60 minutes of use left. Enter 500 psi in the reserve box to plan to that standard. On the example below, that costs 42 minutes of the 224.

Some charts count every psi down to zero. Intermountain’s E cylinder chart gives 3 hours 30 minutes at 1,500 psi and 2 liters a minute, which is the same as 1,500 × 0.28 ÷ 2 with nothing held back. Set the reserve to 0 to match a chart like that.

Where each number comes from

The rider or the supplier gives the cylinder, gauge and flow, the booking gives the times, and your policy sets the reserve and the delay allowance.

• Cylinder size. Ask the rider or the oxygen supplier. For a size that is not listed, divide the liters on the maker’s sheet by the pressure the cylinder is filled to, and enter the result under “Another size”.
• Gauge reading. The gauge on the regulator shows the pressure in the cylinder once the valve is open, and Intermountain’s sheet says to check it with the valve open. It describes a full cylinder as about 2,000 psi. Ask the rider, an escort or the supplier to read it just before the ride, because pressure falls as the oxygen is used.
• Flow setting. The prescribed number on the regulator, in liters a minute. Do not ask the rider to turn it down to stretch the supply: Intermountain’s sheet says oxygen should only be used at the prescribed flow.
• Ride there and ride home. The drive time from the booking, entered separately because the way back can take longer.
• Time at the appointment. The minutes the rider will breathe from this cylinder there. A clinic may supply oxygen during the visit, so ask before the ride and enter 0 only if it does.
• Extra time for delays. Traffic, a late appointment or a slow pickup. The oxygen policy template uses 30 minutes as its example margin.

Worked example

The default inputs are examples. An E cylinder reads 1,800 psi, the flow is 2 liters a minute, and 200 psi stays in the cylinder. The trip is 40 minutes there, 60 minutes at the appointment, 40 minutes home, and 30 minutes allowed for delays.

The cylinder covers the trip with 54 minutes to spare, and the 1,800 psi reading clears the 1,415 psi it needed by 385 psi.

Change the flow to 4 liters a minute and the same cylinder lasts 112 minutes, so it runs out 12 minutes into the ride home. The trip would need a starting reading of 2,629 psi, above 2,216 psi, the top pressure on the maker’s and the hospital’s sheets for these sizes, so one cylinder cannot cover it and the rider needs a second full one. Or keep the flow at 2 and switch to an M6 reading 2,000 psi: it lasts 69 minutes and ends 29 minutes into the appointment.

When does the calculator not fit the rider’s oxygen?

It fits a compressed gas cylinder on continuous flow. Four cases need a different number or a different source.

• A cylinder rated for more than the table. Cylinders with the same letter are not all the same size. One maker’s aluminum ME holds 680 liters at 2,015 psi, a factor of 0.337, and its MD holds 425 liters, a factor of 0.211, where the E and D rows above use 0.28 and 0.16. The table runs short for those, not long. The long-distance guide counts the 680-liter ME as its E size with nothing held back, which is why its E time is longer than the E row above. Choose “Another size” and enter the maker’s figure for an exact answer.
• Pulse-dose devices. Some conserving devices deliver a fixed amount of oxygen per breath and others a fixed amount per minute, according to a 2023 trial in the International Journal of COPD. A setting is not a flow in liters a minute, so ask the supplier for the run time.
• Portable concentrators. MedlinePlus says oxygen is either stored under pressure in tanks or produced by a machine called a concentrator, so a concentrator has no gauge reading to enter. The concentrator power guide covers the van side.
• Liquid oxygen. It is measured in liters of liquid, as the Tampa General handout does, not in psi, and MedlinePlus notes it slowly runs out even when not in use because it evaporates. Ask the supplier for its run time.

What if the cylinder will not last the trip?

Settle it before the trip is confirmed, not at the curb. Federal rules do not let a provider keep a rider with a disability from bringing a respirator or portable oxygen, as long as the hazardous materials rules allow it (49 CFR 37.167(h)), so the question is whether the supply covers the time, not whether the rider may bring it.

• Ask for a second full cylinder. The oxygen policy template has dispatch ask the rider for a spare, or shorten the wait, before the trip is confirmed.
• Ask the clinic about the visit. If it supplies oxygen during the appointment, the cylinder only has to cover the two rides.
• Leave the flow alone. It is the rider’s prescription, not a setting dispatch or the driver adjusts.
• Know the emergency step. A rider who has trouble breathing on the road is an emergency: pull over and call 911, as the medical emergency guide explains.

Planning oxygen rides in HealthRide

In HealthRide, a trip’s oxygen need is matched against each vehicle’s equipment when you assign it, so the ride does not land on a van that cannot take it. See Fleet. The live map shows ETAs and late warnings, which is how you see a ride running long while the cylinder counts down. Each finished trip keeps its timestamps, and the trip log downloads as a spreadsheet or PDF, so the ride times you enter here can come from past trips instead of guesses. See reports.