The EPA traceability protocol for gaseous calibration standards was revised in 2012.  Among the changes, the certification periods for EPA Protocol Gases were extended because NIST and specialty gas producers have gathered more information about the long-term stability of gas mixtures than was available for the 1997 version of the protocol. Table 2-3 from the protocol gives the maximum certification periods for EPA Protocol Gases.  These periods are applicable to newly certified calibration standards and for previously certified calibration standards. 

Note that producers may elect to certify their products for shorter periods if they do not have confidence in the stability of their products for the listed periods. Some producers are electing to notify their customers about the extended periods and to send out revised certificates of analysis.  Per EPA, the producers can exercise their discretion about the extended certification periods and about the notifications.  Accordingly, BTS will require testers to obtain written documentation from the gas producer as to what the extended expiration date is for a particular cylinder in order for it to be used beyond the expiration date listed on the original certification.