Oxygen tanks are used to deliver supplemental gas for various respiratory conditions and emergency situations. Knowing the precise size of an oxygen cylinder is important for calculating the remaining supply and ensuring timely replacement orders. The size designation dictates the tank’s total capacity and how long the oxygen supply will last at a prescribed flow rate. Determining the correct size involves examining permanent markings, taking physical measurements, and understanding the standardized codes used by manufacturers.
Locating and Interpreting Tank Markings
The most reliable method for identifying a cylinder’s size is by reading the permanent markings stamped directly into the metal near the top, often referred to as the shoulder or crown. These markings are mandated by regulatory bodies like the U.S. Department of Transportation (DOT) and Transport Canada (TC). The regulatory specification is etched onto the metal, usually alongside the service pressure, which indicates the maximum safe filling pressure in pounds per square inch (PSI).
The manufacturer’s code or model number is typically included in this grouping of stamped information. It is here that the specific size designation, such as D, E, or M6, is often found. Users should inspect the neck of the cylinder for the largest and most obvious letter or letter-number combination, which serves as the industry-standard size identifier. While the stamped markings are permanent, some cylinders may also feature a regulatory label or sticker on the collar indicating the cylinder type, which can serve as a quick reference.
Identifying Size by Physical Dimensions
If the stamped markings are illegible due to wear or a label is missing, the tank’s size can be approximated by measuring its physical dimensions. This method serves as a useful secondary check or a primary identification when the codes are obscured. To measure the height accurately, place the measuring tape at the base of the cylinder and extend it to the top of the metal neck, deliberately excluding the attached valve or regulator.
Cylinder diameter, measured across the widest part of the base, is also a distinguishing factor. For example, the highly portable M6 cylinder measures approximately 3.2 inches in diameter and about 11.6 to 11.8 inches in height without the valve. A mid-sized E cylinder is significantly taller, often reaching about 25 inches in height, while larger stationary tanks like the H or K size are much taller and wider. By comparing these measured dimensions to common size charts, one can narrow down the tank’s potential designation.
Decoding Standardized Tank Designations
The standardized letter designations, such as D, E, H, and the M-series, directly correlate to the cylinder’s capacity. The industry standard for sizing cylinders is based on the internal water volume the tank can hold, which then determines the volume of compressed gas it contains. The M-series, such as the M6, is used for smaller, highly portable aluminum tanks, with the number indicating a rough measure of capacity in cubic feet.
The M6 cylinder holds approximately 165 liters of oxygen, making it suitable for short-term use or transport. Moving up in size, the D cylinder contains a greater volume, holding around 425 liters, which offers significantly longer use than the M6. The E cylinder, a popular choice for both emergency medical services and personal backup, holds an even larger volume of approximately 680 liters. Stationary tanks, designated as H or K cylinders, are the largest and hold much more gas, suitable for long-term home use where frequent replacement is less feasible.