How to Read the Labels on Dive Cylinders

Note the stampings on the shoulders of these cylinders.

Dive cylinders, or simply "air tanks" as they are more popularly known, are labeled for everything from the results of their last safety check to what kind of gas mixture the tank contains. Many casual divers are reliant upon renting gear from unfamiliar dive shop operators; knowing how to read the labels on a dive cylinder is essential to determine its safety.

Instructions

1. Examine the shoulder of the scuba tank for its stampings. The shoulder is the sloping area at the top of the tank, beneath the valve.

2. Check the first line of material. In North America, this will start with "DOT" or "TC" for Department of Transportation or Transport Canada. That is followed by a alphanumeric code for the grade of steel or aluminum used to make the tank. "3A" and "3AA" mean steel, while "AL" means aluminum. Finally, there is a number that indicates the service pressure of the tank in psi. If the tank is steel, there may be a "+" after that psi rating. This means the tank can withstand up to 10 percent more air pressure. Aluminum tanks never have a "+" rating.

3. Examine the next line for the manufacturer information and serial number, which you can use to track the tank.

4. Check the third line very carefully, as this contains the last hydrostatic test results of the tank. The dates for every hydrostatic test undergone by the tank are stamped here, indicating first the year and then the month. By law, dive cylinders must receive hydrostatic testing every five years. If yours has not received such a test in the last five years, it is out of compliance and potentially dangerous.

5. Look at the bottom and the rest of the tank. While not required, tanks reserved for nitrox and other mixed gases used for deep diving often have a green stripe and a yellow bottom. There may also be a sticker on the side indicating either nitrox, trimix or heliox. If you see any such indicator, the tank should also have a strip of masking tape on it indicating exactly what the gas mix is, such as "Nitrox 32 or O - 32/N -68" indicating a nitrox blend enriched to 32-percent oxygen.

Tips & Warnings

• If you have any questions about the testing or contents of a dive cylinder, do not use it. Unsound dive cylinders can rupture and explode, while breathing mixed gas under the wrong circumstances is potentially fatal.

References

• Scuba Diver Info: Scuba Cylinders
• Fill Express: FAQ About Filing Cylinders