How important is the calibration gas expiry date

Regular calibration of a gas detector with calibration gas is necessary to ensure a good working condition of the instrument. The internal sensor of a single gas detector or the various sensors of a multi-gas detector will be exposed to a particular calibration gas or calibration gas mixture. It is essential to calibrate your gas detector with a calibration gas which has not been exceeded its expiry date. Using expired calibration gas for the calibration of a gas detector could cause improper calibration and could result in a faulty appreciation that the instrument is in an excellent working condition. This fault calibration could finally result in an unsafe working situation.

Calibration gases should be classified into two types, reactive calibration gases and non-reactive calibration gases.

What is a reactive calibration gas?

Reactive calibration gas is a gas mixture which includes at least one component which is reactive. A component which is reactive is a chemical which has some instability under certain conditions and could react with specific materials, moisture, oxygen or other chemicals. A reactive calibration gas could contain hydrogen sulfide, chlorine, sulfur dioxide, ammonia, hydrogen chloride, hydrogen cyanide, etc. A reactive gas is filled in an aluminium cylinder with stainless steel valve that has been treated to minimise reactivity with the reactive gas. A higher concentration of a reactive calibration gas could have a longer shelf life than a reactive calibration gas with a lower concentration. With low reactive gas concentrations, a few reactions could have a much more significant effect on the overall gas mixture compared with the same responses with high reactive gas concentrations. The shelf life of reactive calibration gas is six months to one year. After the shelf life of the calibration gas has expired the concentration of the reactive gas will decrease over time.

Does the quality and size of the cylinder affect the reactive calibration gas?

A well-manufactured gas cylinder has the smoothest possible internal walls. Rough inner walls cause the gas comes into contact with a larger surface which increases reactions with the cylinder material. Therefore the quality of the internal walls of a gas cylinder and the valve material both affect the shelf life of reactive calibration gas.

What is a non-reactive calibration gas?

Non-Reactive calibration gas is a gas mixture which not includes any reactive gas. A non-reactive calibration gas is stable under most conditions and is not affected by moisture, oxygen or other chemicals. Non-Reactive calibration gas is a gas mixture which could include alkane or alkene hydrocarbons (methane, propane, hexane, isobutylene, etc.), nitrogen, hydrogen, carbon monoxide, carbon dioxide, etc. The shelf life of a non-reactive gas is up to 3 years.

Best when used by:
On the label of calibration gases of all reliable gas manufacturers, the expiry date is mentioned as “Use by” or “Best when used by” followed by the month and year.