Page 95 - Praxair - Specialty Gases and Equipment Reference Guide
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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
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