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How To Read SCUBA Tank Markings

   October 10th, 2022   Posted In: How-To   Tags:

How To Read SCUBA Tank Markings

Have you ever stared at a SCUBA tank and wondered how to read all those SCUBA tank markings? There are many things stamped into SCUBA tanks in addition to stickers that might be found on them. Here is a list of typical SCUBA tank markings.

Serial Number

Every individual tank has its own serial number indicated on the SCUBA tank marking. This is important to be able to identify a specific tank and who it might belong to.


Immediately after the serial number you will find the name of the company that made the cylinder. This will be indicated within the first line you see on the SCUBA tank markings. Common manufacturers include Catalina, Luxfer, Faber, and XS SCUBA

Government Approval

Depending on where the tank was made and/or is being used, there will be different government markings on your SCUBA tank. 

DOT: This marking is for tanks manufactured in the United States. DOT stands for Department of Transportation which is the agency that regulates SCUBA tanks in America. 

CTC (or TC): Tanks made in Canada will have this SCUBA tank marking. CTC stands for Canadian Transportation Commission. 

CE: CE represent SCUBA tanks made in the European Union.

Tank Type

SCUBA tanks come in aluminum or steel. You may think it is super easy to determine if a tank is aluminum or steel, but some materials used to paint the tanks look like steel even though they are aluminum.  

The type of tank will be labeled right after the DOT (or respective government stamp) in the middle of the first row of the SCUBA tank markings. For instance, an aluminum tank will usually have ‘AL’ written on it. Aluminum tank markings have varied over the years. In the United States, SCUBA tanks manufactured since 1982 will be labeled as ‘3AL’, with the 3 indicating 3-gauge.

Tanks made in Canada will be labeled ‘3ALM’. Aluminum tanks may also have ‘SP6498’ or ‘E6498’ written on them.

Steel tanks are more straightforward. They will be labeled with ‘3AA’ and are made of chrome-molybdenum steel. The older carbon steel tanks will be labeled ‘3A’, but there are few left in the world. 

Working Pressure

Different sizes of cylinders will have different working pressures to which the tank can be filled. The SCUBA tank markings found right after the type of material the tank is has numbers. These numbers indicate the working pressure. These pressures will be in PSI on tanks made in the United States and in bar on tanks made in Canada or the European Union. For example, an aluminum 80 tank made in the United States will have AL 3000 to indicate an aluminum tank that can be filled to 3000 PSI. Tanks may also be labeled with ‘LP’ for low pressure or ‘HP’ for high pressure.

If a tank has a ‘+’ symbol next to the working pressure tank marking, then this tank can be filled up to 10% more than the working pressure indicated on the tank. This can occur with some steel tanks.

Hydrostatic Test Date

Every SCUBA tank requires a hydrostatic test, or hydro for short, every 2-5 years depending on the tank. These markings will be stamped onto the shoulder of the tank. The original hydro test date can be found next to the manufacturer’s details. The subsequent hydro tests will be stamped onto the shoulder of the tank or anywhere there is space, often leaving the other dates in place. Thus, some SCUBA tanks will have many hydro dates stamped on them depending on how old the tank is. 

The SCUBA tank markings for the hydro test will have the month of the inspection followed by a letter that represents who inspected it followed by the year it was performed. For instance, a tank that was serviced for hydro in October 2022 could have ‘10A22’ on it, or some other letter in the middle. Sometimes it takes effort to find the date that is most recent to indicate if a tank is within the hydro range of 5 years. 

Visual Inspection Stickers

Although visual inspection, VIP for short, dates are stickers and not actually stamped into the tank, they are important to also recognize. A VIP is performed every year on a tank. The month and year the VIP was performed will be hole punched out of the sticker.


Another label you might find on a SCUBA tank is a sticker labeled ‘Nitrox’ or ‘Enriched Air’. Nitrox is a breathing gas that is enriched with oxygen up to 40% for recreational divers that are certified to use this type of gas.

Now you can look at a SCUBA tank and understand how to read SCUBA tank markings. This important for the safety of the diver and those that fill the tanks. 

Candace is an avid scuba diver and freelance writer with a PhD in Biomedicine. She has been diving since 2002 and is currently a PADI IDC Staff Instructor. When she is not instructing, she enjoys writing about scuba and volunteering at the local aquarium where she dives with the sharks!

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