Page 95 - Praxair - Specialty Gases and Equipment Solutions

Behind The Scenes

Mixture – Safety and Quality Mixture Grades and Specifications
Safety and quality considerations limit the mixtures Praxair mixtures are grouped into two basic
we can offer – among these are: categories, environmental and standard. Please
refer to the table on page C•92 for complete
■ Fuel – Oxidizer Mixtures
Praxair will complete a safety review for any mixtures specifications of all available grades.
containing flammable and oxidizing components. Environmental Grades have been developed to meet
Each mixture is evaluated to ensure the flammable the stringent requirements of specific environmental
concentration is well below the flammable limits. applications such as EPA Protocols, I&M (Inspection and
Praxair will determine if the mixture must be made Maintenance) emission standards, and mixtures requiring
at reduced pressure. Final mixture pressures are NIST Traceability. In all cases, specifications have been
based on BTU calculations. developed to meet industry standards or, in some cases,
to meet regulatory requirements.
■ Vapor Pressure Restrictions
Mixtures containing low vapor pressure components When EPA Protocols are not necessary, but NIST trace-
are generally made at reduced pressures. Pressure ability is desired, Praxair’s Master grades provide the
reduction helps prevent condensation of less volatile highest degree of accuracy and confidence for your most
component and ensures mixture homogeneity. demanding applications. These mixtures are prepared
Computer modeling is used to generate phase gravimetrically on high-precision, electronic balances or
envelopes for mixture evaluation and determination using dynamic blenders.
of appropriate pressures. The accuracy from these methods may exceed the accu-
Where applicable, Praxair may recommend low-pressure racy of most analytical instruments. Praxair produces three
containers to maximize the volume of contents. Refer to grades within the Master grade category; Primary, Certified,
page A•12 for details. and Dynamic-Blend. The minor component(s) are analyzed
and certified by Praxair and are traceable to NIST reference
■ Reactive Gas Mixtures
Mixture stability is assessed to help ensure the requested material.
components do not react with each other or with the For general purposes, Praxair’s Standard Grades are
cylinder. Primary consideration is given to safety and the available as Primary and Certified. These analyzed stan-
potential by-products created by a chemical reaction. dards are typically used for high volume applications where
Integrity of analytical accuracy is also evaluated. A the blending precision and accuracy of the Master grade is
feasibility review is peformed prior to mixture preparation. not required. Standard grade mixtures are prepared using
Where applicable, Praxair will provide aluminum or gravimetric, volumetric, or partial pressure methods. As in
specially treated cylinders for low concentration reactive the Master grades, the minor component(s) are analyzed
gas mixtures. See page A•11 for details on aluminum and certified. The more economical Non-Certified grade is
cylinders. suitable for applications that do not require analytical
The stability of certain gas mixtures can be affected by certification.
the length of time they are stored, as well as the storage If your requirements call for specifications that fall outside
temperature. To ensure the integrity of gas mixtures, of these defined grades, a custom standard will include the
storage time and temperature for susceptible mixtures exact specifications you need.
should be monitored.
If you are uncertain about which grade to choose,
Praxair technical support staff can provide recom-
mendations based on specific applications and
requirements. Call your Praxair representative or your
nearest customer service location for assistance!

i

Contact the North America Technical Support
Center at 877-PRAXAIR for assistance!
Section C – Mixtures

C•94 1-877-PRAXAIR www.praxairdirect.com