Last Updated: February 8, 2023
One of the most important aspects to planning a dive is the scuba tank. You have to know how much pressure there is in the tank, what its capacity is, when the government made its approval and a host of other information. These will come stamped near the top of the tank.
This guide will take you through the basics on how to read the markings on a scuba tank. It will include the manufacturer, serial number, materials it comprises, government regulatory approvals, hydrostatic dates, the tank’s capacity and many others.
When you understand what they mean, it will make things a lot easier. You’ll know for how long you can dive, which will provide a reference of time. Actually, knowing the markings is an essential safety feature so you won’t miscalculate.
What Do Engraved Markings on Scuba Tanks Include?
When you look at a scuba tank, you will see markings that include things like:
- Capacity (often indicated in cubic feet via BARS or PSI)
- The pressure amount to fill, also called “Service Pressure” (some allow expanded capacity)
- Manufacturer of the cylinder
- Hydrostatic date (indicates how old the cylinder is)
- Government regulatory markings (each country has their own)
- Cylinder’s serial number
- Cylinder’s material (aluminum or steel)
Cylinder Manufacturer Markings
There are many markings available on tank cylinders. So, even if you can identify what they are, it’s imperative you look up the specific manufacturer and the tank in question. You want to be 100% clear of the materials, working pressure, government approval, dates and so forth.
Markings to Identify the Government Approval
Every country around the world has their own markings for scuba tanks. The most common ones will be from either Canada or the United States. These will be either Transport Canada, marked with a CTC or TC. For the US Department of Transportation, DOT are the letters to indicate its approval. The European Union marks theirs with CE.
There will also be some sort of certification marking by an inspector. This will show as something like “A.” These will be different depending on how a country classifies their inspections.
Markings That Tell What Metal They Are Made of
There are two basic metals almost all scuba tanks are made from. These are aluminum and steel. However, specific types of steel or aluminum have their own particular markings.
- 3A (Carbon Steel or Molybdenum Steel): The first scuba tanks comprise some variation of steel. These have poor resistance against corrosion and there are very few in circulation.
- 3AA (Chromium-Molybdenum Steel): Another variation of steel that holds up slightly better against corrosion.
- 3AL or 3ALM (Aluminum): Code used by Canada and the US since 1982 to identify aluminum tanks. However, these can be difficult to pinpoint if the tank is older than this. Some come with a stamp like SP6498 or E6498.
Markings to Indicate Work Pressure
The work pressure of a scuba tank will tell you how much oxygen is available for use, what capacity it can hold, the pressure measurement and if it has overfill capability.
The USA uses PSI (pounds per square inch) to indicate pressure whereas Canada and Europe use BAR (poundage measurement equal to sea level pressure). If there is a “+” next to the hydrostatic date and/or the PSI number, you can fill the tank about 10% above capacity.
Other Scuba Tank Markings
There are other crucial markings visible on a scuba tank such as the serial number and manufacturer. Also, date of testing for the tank should be prominent. These sit in the center of the inspection code, alongside the government approval stamp.
Common Engravings Found on SCUBA Cylinders
| Engraving | What it Means |
| DOT | Department of Transportation (U.S.) |
| M9542 | DOT Manufacturer Facility Number |
| TC or CTC | Transport Canada |
| SU7694 | Special Permit Number (Canada) |
| 3442
3300 2400 |
PSI for cylinder pressure |
| 237
230 207 184 |
BAR for cylinder pressure |
| 3AL | 3-guage aluminum (U.S.) |
| 3ALM | 3-gauge aluminum (Canada) |
| 3A or 3AA | Molybdenum Steel |
| 01A20 | Hydrostatic inspection date example (different numbers depending on the date) |
| “+” | Can overfill by 10% when sitting next to hydro or capacity |
| A | Independent Inspector |
| Catalina | Manufacturer |
| Faber | Manufacturer |
| Luxfer | Manufacturer |
| HP | High Pressure (3300 to 3500 PSI) |
| LP | Low Pressure (2250 to 2400 PSI) |
| LP95 | Model Number example indicating LP at 95 cubic feet |
| S0-40 | Model Number example indicating 40 cubic feet |
| XS-80 | Manufacturer and model number indicating 80 cubic feet |
| S080 | Model Number Example indicating 80 cubic feet |
| P869232 | Standard Serial Number example (different models will have varying numbers and letters) |
| TP5250 | Test Procedure (indicates hydrostatic retest in PSI) |
Frequently Asked Questions
How to tell if a scuba tank is aluminum or steel?
If the metal markings are obscure or nonexistent on a scuba tank, use a magnet. It won’t stick to aluminum but it will stick to steel.
How do you check the hydro date on a scuba tank?
The hydro date will often be the last marking near the top. The first number indicates the year with a backslash (/) followed by the month. For instance, you will know the hydro date is May 2008 when you see “2008/5.”
What is the wall thickness of a scuba tank?
Scuba cylinders often measure in millimeters (mm). They are usually somewhere between four and six mm for steel and upwards of 11 mm or more for aluminum.
What is the standard size scuba tank?
The standard size scuba tank is 625 mm long with a diameter of 178 mm. This means they can usually hold anywhere between 80 to 100 cubic feet of air pressure.
Do scuba tanks expire?
Scuba tanks do expire. The cylinder must successfully pass the visual inspection and the hydrostatic test. The visual inspection is done once a year. The hydrostatic test once every 5 years in the US.
Once your tank passes an inspection, it will be given a sticker or a stamp with an expiration date. If it is expired (due for an inspection) and it fails the inspection, the tank should be replaced as soon as possible.
Both aluminum and steel scuba tanks can last for 10-15 years (steel tanks for even longer, assuming they are properly maintained).
How long does a scuba tank last?
An average recreational tank containing 200 bars or 12 L of air should last you for 60 minutes. However, several factors come into play while determining the lifespan of an air cylinder.
Do scuba tanks float?
No, scuba tanks do not float as they are negatively buoyant. However, some aluminum scuba tanks can float when empty due to losing the weight of the compressed air.
Final Thoughts
Knowing what is the right way to read scuba tank markings is an essential step in enjoying a safe dive. But, even if you can read them, it’s important to also refer to the manufacturer’s instructions for detailed specifics about the tank.
Taking all the necessary precautions will ensure a great adventure, while being smart about how long you can be in the water.
My unbounded love for the oceans and everything it has to offer motivated me to pursue my passion and become a professional scuba diving instructor.
I keep reading, exploring, and learning more about scuba diving and the underwater world all the time, so I’m excited to share my knowledge with fellow scuba enthusiasts and hopefully contribute a little to your development as a diver. I want people to fall in love with the oceans with as much passion as I have. Read more about me here.