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Specialty Gas FAQs

Are all 6.0 grade gases the same? plus minus

No they are not, and looking only at the headline purity of a gas can be very misleading. A gas that is stated as 6.0 grade means there is a maximum of 1 ppm total impurities, but it does not tell us what those impurities are. Knowing specifically which impurities are present and in what concentrations is critically important in almost all analytical techniques. It can be the difference between high accuracy analytical measurements, and damaging expensive instrument components.

Even though the overall purity of a gas might be stated as the same, the impurity specifications themselves can be very different from one supplier to another.

If you do not know which impurities are important, our community of experts are on hand to give advice on the best specification of gas for your particular analytical technique.

Very often - yes. But whilst it is common to indicate the quality of a gas in terms of overall purity or grade, it is more often the presence and/or concentration of specific impurities that result in sub-optimal performance of analytical equipment. This can be in the form of damage to expensive instrument components, higher limits of detection, or increased analytical uncertainty.

The presence of oxygen or moisture in ultra-high purity gases can very often damage analytical instrumentation and affect the quality of measurements. This is why Air Products BIP® technology, which removes these critical impurities from ultra-high purity gas, is widely considered to be the benchmark.

Every analytical technique is different. Often oxygen and moisture can be harmful impurities, which explains the popularity of Air Products BIP® technology. For other techniques, hydrocarbons, CO, CO2, or other gases can have a negative impact on instrument performance. Most manufacturers of analytical instrumentation will give guidance on the specifications of gases needed for best performance. Some will even highlight the critical impurities to avoid, but many do not. If you do not know, and need advice, our team of experts are on hand to provide it.

Always look beyond the overall gas purity or grade, and pay special attention to the impurity specifications of all ultra-high purity gases. Once you have selected a gas with the optimum specification, you can then get even more value by thinking about economy, efficiency, and sustainability. As well as delivering ultra-high purity gases with unrivalled specifications of critical impurities like oxygen and moisture, BIP® technology provides a number of other important benefits, like more useable gas per cylinder, and the elimination of external in-line purification systems that are costly and inconvenient to maintain.

What are the key factors to look out for when buying a calibration gas mixture? plus minus


Traceability of measurement requires an unbroken chain of comparisons to stated references, each with a stated uncertainty. The objective is to deliver national and international comparability. All calibration gas mixtures offered by Air Products are traceable to international standards.

Traceable calibrations automatically provide our customers with the means to obtain consistent data over time, even when one mixture is replaced by another, and it allows full comparability of data obtained from similar measurements taken around the world.


Accuracy and uncertainty defines the quality of a measurement and allows the user of a calibration gas mixture to assess the reliability of a stated value.

Air Products has been at the forefront of gas mixture preparation for many years and has worked tirelessly in improving the accuracy of our stated measurements. Combining our expert knowledge with modern ultra-high accuracy measurement instruments, state of the art filling technologies across all of our worldwide special gases facilities, and a vast library of reference materials from national measurement institutes, allows us to deliver market-leading accuracy to our customers around the globe.

Uniquely to Air Products, the standard uncertainty of measurement for all our certified gas mixtures is calculated individually for each mixture component, and for many components we offer market leading uncertainties down to +/- 0.05 %. This is a clear indication of the highest accuracy and Air Products' leadership position in this field.

Accuracy is helping our customers to be more competitive, ensure compliance to regulations, increase their profitability, as well as allowing them to achieve technical excellence across a wide range of industries and applications.


Gas mixture stability is a measurement of how long a mixture can be confidently used after its initial certification by the manufacturer.

Air Products' leading position in the field of mixture stability is based on a range of factors. For each and every mixture produce, we consider the optimum cylinder and valve selection, the best surface treatments and cylinder preparation techniques, and the selection of ultra-high purity component gases. When combined with our advanced filling methods and analytical techniques, Air Products is able to create extremely stable blends that will remain within tight specifications for up to 10 years.

Experis® cylinder treatments reflect decades of research and development, and have allowed Air Products to repeatedly demonstrate market-leading stability of a wide range of mixtures. Even mixtures of highly reactive components with concentrations measured in parts per billion are offered with shelf lives of up to 3 years. Consequently, Air Products has become a trusted supplier of treated cylinders to national laboratories and leading gas metrology institutes, receiving endorsements from around the world. In this way, Air Products is a true leader in advancing the science of gas mixture stability.

This innovative and customer focused approach allows our customers to reduce inventory costs versus shorter shelf life equivalents, minimise the inconvenience of cylinder changeovers, and simplify legislative or quality compliance in a diverse range industries. An Air Products gas mixture provides added peace of mind that it will remain within a tight specification for years to come.

An ISO 17025 accredited mixture is a commonly used term to describe a calibration gas mixture that has been certified within an ISO 17025 accreditation scope. Air Products can supply accredited gas mixtures for air emissions monitoring, vehicle exhaust measurement, and for natural gas analysis markets.

The shelf life of an Air Products' calibration gas mixture is our assurance that the mixture will remain within specification for an extended period of time. You will see the shelf life on the cylinder labelling and on our certificates of analysis. Longer shelf lives can allow customers to lower their costs by reducing re-order frequency.

Air Products has developed a number of proprietary cylinder treatment technologies for different gas mixture compositions that result in proven mixture stability, even for very technically challenging mixtures. Many of the world's leading gas metrology institutes rely on Air Products for provision of Experis® treated gas cylinders for the purpose of preparing primary reference materials.

How many bump tests can I perform on my instrument, using a single canister? plus minus

The instrument manufacturer will normally recommend the optimum flow rate of gas needed to test their equipment in their operating procedures. Selecting a suitable fixed flow regulator will maximise the number of tests possible.

Using a demand-flow regulator for instruments fitted with internal pumps can further optimise the process. (These units limit the flow of gas to that demanded by the instrument and means there is no wasted gas.)

Our largest canisters hold approximately 110 gaseous litres, so an instrument with a response time of 10 seconds using a fixed flow of gas of 1.0 lpm might be tested several hundred times using this type of canister.

No - It is simple. Watch this video to see how easy it is to bump test a portable gas detector using an Air Products non-refillable canister.

Calibration is the activity of checking, by comparison with a standard, the accuracy of the equipment. It may also include an adjustment of the instrument to bring it into alignment with the standard.

Bump testing is the application of a test gas to the equipment only to verify the functionality of its sensors and alarms, such as checking does it work, or not.

If we consider that the output of a typical sensor in clean air is zero, this is the same as the output of a non-functioning sensor. So, exposing the instrument and sensors to a test gas is the only way to know it will respond to a hazardous gas that may be present in the atmosphere. This is bump testing.

The latest Air Products canister recycler tool has been specifically designed for ease of use, enabling depressurisation of used non-refillable canisters, ensuring they can be safely recycled.

In the European Union, non-pressurised canisters can be recycled through the normal waste stream as non-hazardous products. For countries outside the European Union, the relevant local authority should be consulted for guidance.

Our low torque, portable recycler is designed to work with Air Products valves marked ISO 11118. (This can be found stamped on the shoulders of the valve.) For other Air Products valve types and aerosol canisters the fixed position, universal recycler can be used.