D Cylinder (Factor 0.16)
E Cylinder (Factor 0.28)
M Cylinder (Factor 1.56)
G Cylinder (Factor 2.41)
H/K Cylinder (Factor 3.14)
Standard safety buffer is usually 200 PSI.
Available Pressure:0 PSI
Total Minutes Remaining:0 min
Time Remaining:0 hr 0 min
function calculateO2Duration() {
// 1. Get input values
var tankFactor = parseFloat(document.getElementById('tankType').value);
var pressure = parseFloat(document.getElementById('currentPressure').value);
var flowRate = parseFloat(document.getElementById('flowRate').value);
var residual = parseFloat(document.getElementById('residualPressure').value);
// 2. Element references for output
var resultsDiv = document.getElementById('results');
var displayPressure = document.getElementById('displayAvailablePressure');
var displayMinutes = document.getElementById('displayTotalMinutes');
var displayFormatted = document.getElementById('displayTimeFormatted');
// 3. Validation
if (isNaN(pressure) || isNaN(flowRate) || isNaN(residual)) {
alert("Please enter valid numbers for Pressure, Flow Rate, and Residual Pressure.");
return;
}
if (flowRate <= 0) {
alert("Flow Rate must be greater than 0.");
return;
}
// 4. Logic Calculation
// Formula: Duration (min) = (Current Pressure – Residual Pressure) * Tank Factor / Flow Rate
var availablePressure = pressure – residual;
// Handle case where pressure is below residual
if (availablePressure 0) {
displayFormatted.innerHTML = hours + " hr " + minutes + " min";
} else {
displayFormatted.innerHTML = minutes + " min";
}
}
How to Calculate O2 Flow Rate and Tank Duration
In respiratory care and emergency medicine, ensuring a patient has a continuous supply of oxygen is critical. While the "flow rate" is prescribed by a physician (measured in Liters Per Minute or LPM), the calculation most often performed by nurses, respiratory therapists, and EMTs is the Tank Duration Calculation. This determines how long an oxygen cylinder will last at a specific flow rate before it runs out.
The Oxygen Duration Formula
To calculate how many minutes of oxygen remain in a cylinder, you use the following standard formula:
Gauge Pressure (PSI): The amount of pressure currently shown on the regulator's gauge. A full tank typically holds 2000 to 2200 PSI.
Safe Residual Pressure (PSI): You never want to drain a tank completely to 0 PSI, as this can damage the tank or allow contaminants in. The standard safety buffer is 200 PSI.
Flow Rate (LPM): The liters of oxygen per minute being delivered to the patient (e.g., 2 LPM via nasal cannula).
Cylinder Factor: A constant number derived from the physical volume of the specific tank size.
Oxygen Cylinder Conversion Factors
Different tanks hold different volumes of gas. You must know which letter designation corresponds to your tank to use the correct factor.
Result: The tank will last for 1 hour and 10 minutes.
Frequently Asked Questions
Why do we subtract 200 PSI?
Subtracting 200 PSI is a safety precaution commonly known as "Safe Residual Pressure." It ensures the tank is changed before it becomes completely empty, preventing patient hypoxia during the switch-over and protecting the cylinder from internal contamination.
Does Flow Rate affect Oxygen Concentration (FiO2)?
Yes. For a nasal cannula, a general rule of thumb is that every 1 Liter increase in flow rate adds approximately 4% to the fraction of inspired oxygen (FiO2), starting from a baseline of 21% (room air). For example, 1 LPM is roughly 24%, 2 LPM is 28%, and so on.
What is a full tank pressure?
Most standard medical oxygen cylinders are considered full at approximately 2000 to 2200 PSI.