Supplemental oxygen cylinders, often called tanks, are common in respiratory care, providing gas to patients at home or during transport. These pressurized containers rely on precise labeling for safety and proper usage, but the markings can be confusing. Understanding these designations is important for managing the supply and knowing how long the oxygen will last. The marking “CF2” is one such designation that relates directly to the delivery of the gas.
Decoding the CF2 Designation
The “CF2” designation most frequently refers to a setting on the flow regulator attached to the oxygen tank. “CF” stands for Continuous Flow, and the number “2” indicates the flow rate in Liters Per Minute (LPM). Continuous flow delivers oxygen at a steady, uninterrupted rate, regardless of whether the user is inhaling or exhaling. This setting differs from “pulse” or “demand” flow, which releases oxygen only when the user takes a breath, conserving the tank’s contents.
A regulator dial marked “CF2” instructs the device to release oxygen at a rate of 2 LPM while the tank is open. This is a common prescription for supplemental oxygen therapy. While “CF2” might occasionally denote a small cylinder with a 2 cubic foot capacity in older systems, the primary interpretation for users is the continuous flow setting. Recognizing this marking as a flow rate setting is important because the flow rate determines how quickly the tank empties.
Standard Oxygen Tank Sizing and Capacity
While “CF2” references flow rate, the cylinder’s physical capacity is designated by a standardized letter system. The total volume of oxygen a tank holds is measured in cubic feet or liters, defined by its dimensions and fill pressure.
Small, portable cylinders used for ambulation are typically D or E size tanks. A D-size cylinder holds about 350 liters of oxygen when full, and an E-size holds about 625 liters. Larger, stationary tanks for extended home supply are labeled H or K, holding thousands of liters. These tanks are often filled to high pressure, around 2000 pounds per square inch (psi). The tank size letter and pressure define the total usable volume of gas, which is necessary for calculating duration.
Practical Application: Calculating Remaining Duration
Knowing the tank size, pressure, and flow rate allows users to estimate accurately how long the oxygen supply will last. Caregivers and patients use a specific formula for this calculation.
The formula is: Duration (in minutes) equals the remaining tank pressure (in psi) multiplied by a specific Cylinder Factor, then divided by the prescribed flow rate (in LPM). The Cylinder Factor is a constant unique to each tank size that translates tank pressure into an equivalent volume of oxygen. For example, the factor for a D tank is 0.16, and for an E tank is 0.28.
If an E-tank has a pressure reading of 1,500 psi and the flow rate is set to 2 LPM (the “CF2” setting), the calculation is (1,500 psi x 0.28) / 2 LPM. This equals 210 minutes, or 3.5 hours.