How to Read Compressed Gas Cylinder Markings

If you’ve ever used a compressed gas cylinder, you’ve likely noticed the markings on the shoulder of the tank. Cylinders are stamped to denote the specifications of how the cylinder was made, a unique serial number, the date the cylinder was made, the owner of the cylinder, when the cylinder will need to be retested and more. We’ve made a quick guide to show you around these markings.​

1. ​Cylinder Specification

• The first series of letters is the specification that was used in manufacturing the cylinder itself. This is most commonly DOT–Department of Transportation, but could also be ICC for older US tanks, or CTC for Canadian tanks.
• The set of numbers specificities the type of material of construction (e.g., 3AA or 3A for steel, or 3AL for aluminum).
• Next you’ll find the rated pressure in pounds per square inch (e.g., 2,265 psi).

2. ​Cylinder SERIAL NUMBER

3. ​Date of Manufacture

• This date (month-year) indicates the original hydrostatic test.

4. Neck Ring Identification

• Displays the name of the current owner of the cylinder.

5. ​Retest Markings

• The format for a retest marking is: Month-Facility-Year-Plus Rating-Star Stamp
• The + Symbol (Plus Rating) indicates the cylinder qualifies for 10% overfill.
• The ★ Symbol (Star Stamp) indicates that the cylinder meets the requirements for 10-year retest.

6. Cylinder Manufacturer’s Inspection Marking

7. Cylinder Tare (Empty) Weight

8. Gas Cylinder Label

• This sticker indicates the type of gas in a cylinder, as well as its properties and hazards.

Cylinder DifferentiatioN

Gas service for the cylinder can be differentiated by:

• the valve installed (which is gas specific and stamped with the CGA number) 
• the label on the cylinder (Label must be present or cylinder must not be used)

No compressed gas cylinder should be accepted for use that does not legibly identify its contents by name. If the labeling on a cylinder becomes unclear or an attached tag is defaced to the point the contents cannot be identified, the cylinder should be marked "contents unknown" and returned directly to the manufacturer.

Do not use cylinder color in order to determine cylinder content. Gas cylinders are often color coded but because the codes are not standardized between different vendors, cylinder color cannot be safely used for gas content identification. Even though medical gas cylinders do use industry standard color coding, the paint color may change over time and with weathering, so it is only safe to identify a cylinder’s contents by its label.

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