Understanding Your Calibration Gas Cylinder Label

We want to help you make sense of the label on your calibration gas cylinder. What's in the cylinder? Is it still good or is it expired? We also want to explain how to determine if the cylinder still contains gas. Read on to learn more.

Identifying What Is In the Calibration Gas Cylinder

We sell three different manufacturers of calibration gas (all OEMs). Their labels are all fairly similar. Using the below picture, we will parse out what's going on.

The "components" of the gas is the list of the four gases in the bottle and the one gas used to "balance" or stabilize the component gases. In our example, the four gases are hydrogen sulfide, carbon monoxide, methane, and oxygen. These, of course, are the four gases a typical confined space monitor detects. The balance gas component is nitrogen.

Note that the concentrations of the component gases are also listed. Unfortunately, most confined space gas monitors do not use the same calibration gas concentrations for calibration. BW uses a different concentration of the component gases than MSA, for example.

When we speak of the size of a calibration gas cylinder, we typically refer to the volume the cylinder holds, not its physical dimensions. In this case, the size is 58 liters. The most common sizes are 34L or 58L.

The part number listed is often not has helpful as one might think. Always confirm the gas is correct by comparing the component gas concentrations with the gas required by the manufacturer of the gas monitor being calibrated.

Identifying the Cylinder Expiration Date

Generally, the most common 4-gas calibration gas mixtures, like the one in our picture, are good for two years from the date of manufacturer. After two years, the hydrogen sulfide gas in particular, begins to degrade. When this happens your monitor will fail calibration because of bad gas, not because something is wrong with the monitor.

In order to make sure your calibration gas cylinder is not expired, look for the manufacturer or fill date. In our example, the fill date is 12/10/21. This means that after 12/10/23, the gas must be taken out of service. It is no longer reliable.

Identifying if the Cylinder of Gas is Empty

The only way to determine, roughly, how much gas is in the cylinder is with a fixed flow regulator or demand flow regulator with a gauge. An example of each is picture below.

If you have a regulator with a gauge (like the ones pictured here), this is how you determine how much gas is in the cylinder. First, you locate the PSI rating on the cylinder. In our cylinder example, on the label it states that the cylinder is filled to 500 PSIG. Second, put your regulator on the cylinder and observe the PSI reading.

When the cylinder is full, the regulator will read at or near the cylinders PSI. In our example, this is 500 PSI. As the cylinder is used up, the PSI reading will gradually decline. The regulators pictured above show what a regulator reads when the cylinder is empty. The needle in the gauge is all the way to the left.

We hope this helps. As usual, don't hesitate to call us with any questions. We are always here to help.