Scuba diving is an exciting sport requiring proper gear and equipment to ensure a safe and enjoyable experience. One of the most important pieces of equipment is the scuba cylinder or tank, providing divers with the necessary gas to breathe underwater.
Scuba tanks come in different materials, including aluminum and steel. Understanding how to read scuba tank markings and ensuring the tank meets specific requirements is essential to dive safely. In this post, we’ll explore the different types of scuba cylinders, the markings you need to know, and what to look for to ensure your tank meets the necessary safety standards.
This post is part of a series describing scuba tanks characteristics and features in more detail. If you want to improve your diving knowledge, check out my other post on scuba tank valves.
Why do you need to know how to read scuba tank markings?
Whether you are renting or have your own scuba tanks, knowing about their markings is essential. Tank markings provide you with essential information on material, serial number, capacity and maximum filling capacity and last date of hydrostatic testing.
If you are renting your scuba tanks, knowing the last time your scuba tank was hydrostatically tested is quite important. It will ensure that you are renting an essential piece of gear that is safe.
On the other hand, if you are buying your own scuba tanks, markings will be important in case you would like to sell them in the future.
Let’s take a quick look at the most common scuba tank markings and their meaning.
Overview of scuba tank markings
Stamped, engraved, markings on scuba tanks include date of hydrostatic testing, material (A= aluminum, AA = steel) and serial number. Although tank markings may change from country to country, they are always located on the shoulder of the cylinders.
In most cases, scuba tank markings will indicate the following information:
- Manufacturer
- Serial number of the cylinder
- Material the cylinder is made of (aluminum or steel)
- Tank capacity
- Service pressure (maximum amount of pressure the tank can be fille to)
- Original hydrostatic date
- Name or abbreviation of the government agency imposing minimum safety requirements (this changes from country to country)
Scuba Tank Markings in the United States
Scuba tanks in the United States are measured in cubic feet. The most common size is 80 cubic feet. They come in multiple sizes and some divers prefer to use a 100 cu. ft. tank since it holds more gas. Less common are pony bottles, that range in size from 40 to 63 cu. ft.
When it comes to materials, the most common materials in the United States are steel and aluminum. Steel tanks are generally preferred by technical divers, whereas aluminum tanks are preferred by sidemount divers, or by divers that use stage cylinders.
Scuba tank markings in the United States include the following:
- Abbreviation of the US Regulatory Authority (DOT stands for Department of Transportation)
- US Specification for the material (3AL means 3-gauge aluminum)
- Tank’s service pressure expressed in psi (usually 3000)
- Unique Serial number of the cylinder (usually a six digit number preceeded by a letter)
- Tank manufacturer (e.g. LUXFER)
- Original Hydrostatic test date (expressed in month/year)
- Tank’s capacity in cubic feet (e.g. S080 means 80 cu. ft. at 3000 psi)
Note that if your tank is made of steel, you will read “3AA” instead of “3AL”. According to the DOT regulations, scuba tanks must be hydrostatically tested every 5 years.
Scuba Tank Markings in Canada
If you are buying or renting a scuba tank in Canada, the marking structure does not change much from the US one. The initial part of the marking will differ, reflecting the Canadian regulatory authority markings instead of the US ones.
Scuba tank markings in Canada include the following:
- Abbreviation of the Canadian regulatory authority (TC means Transport Canada, showing the tank meets canadian specifications)
- Canadian specification for the material (3ALM means 3-gauge aluminum)
- Tank’s service pressure expressed in bar (usually 207)
- Tank’s unique Serial number (usually a six digit number preceeded by a letter)
- Tank manufacturer (e.g. LUXFER)
- Original Hydrostatic test date (expressed in month/year)
- Tank’s capacity in cubic feet (e.g. S080 means 80 cu. ft. at 207 bar)
Note that in Canada, regulatory authority markings are mostly expressed in Bar instead of Psi, and that cylinder capacity can be expressed in liters instead of cubic feet.
Scuba Tank Markings in the European Union
In the European Union, scuba tank markings are somewhat more complicated than in the US and Canada. This is due to the European Pressure Equipment Directive, that tries to harmonize markings across all european States. Note that despite Brexit, the UK still follows the European Union markings system.
Scuba tank markings in the European Union include the following:
- Thread specification code, ensuring the correct valve is used with your scuba cylinder (e.g. M25x2)
- Country of manufacture (e.g. UK for United Kingdom or IT for Italy)
- Cylinder manufacturer (note that in teh EU there are many cylinder manufacturers, you can find LUXFER, FABER, Eurocylinder)
- Cylinder Type Number and Serial Number (e.g. P3173V) – This number is recorded by the manufacturer meaning that, if ever necessary, the entire manufacturing history of your cylinder is traceable
- Construction Alloy (e.g. AA6061 T6)
- Design Minimum Wall Thickness expressed in millimiters (11,6MM)
- Empty Weight of Cylinder Only (expressed in kg)
- Minimum Water Capacity (expressed in liters)
- Working Pressure expressed in Bar (PW 232 BAR) – maximum pressure the cylinder should be filled to
- Test Pressure expressed in Bar (PT 348 BAR) – maximum pressure the cylinder should be tested to
- Service Pressure (PS 287 BAR AT 60°C) – maximum service pressure and operating temperature for which the cylinder design is approved
- CE marking. This is the mark of Conformity and Notified Body Reference Number according to the Pressure Equipment Directive 97/23/EC
- Year and Quarter of year of initial test
Scuba Tank Markings in Asia
Although the general structure of tank markings does not differ much from the structure you can find in the US, Canada or Europe, local regulations differ from country to country.
In particular, the following elements in relation to scuba tanks can be different:
- frequency of hydrostatic tests
- frequency of visual inspection
- shape and form of visual inspection stickers
Conclusion
SCUBA tank markings are an essential safety element in scuba diving. I often find that students overlook cylinder markings past their open water diver, divemaster or even instructor exam.
Consider that a properly maintained and serviced scuba cylinder is the most essential piece of scuba gear you will ever use. I strongly encourage you to take a closer look at the markings every time you will be using a scuba cylinder. In particular, you should pay attention to the material (aluminum tanks tend to be lighter), last date of hydrostatic testing (if greater than 5 years, I would change tank), and last date of visual inspection (if greater than 1 year I would ask the dive shop why the tank was not serviced).