C. Cylinder Gas Audits (CGA)

Regulatory references:
Appendix F to Part 60 – Procedure 1, section 5.1 (Auditing Requirements)

Pre-Audit Activities:
1. Consult the User Guide in StackVision, if needed. Open up the Linearity/CGA editor first and then click on “Help” at the Main Menu.
2. Successive quarterly audits shall occur no closer than 2 months.
3. CGAs may be conducted in three of four calendar quarters, but in no more than three quarters in succession. A CGA is not required in the calendar quarter that a RATA is conducted.
4. CGAs are not required for calendar quarters in which the affected facility does not operate. [5.1.4]
5. Verify that you have the correct blend of gas cylinders needed to perform a CGA.
6. Verify that you have enough gas in each cylinder to allow you to perform 6-7 runs (several runs for troubleshooting and then three good runs for the actual audit).
7. A CGA is not the same as a linearity. A CGA is performed using gas cylinders of two different concentrations, while a linearity is performed using three different concentrations.
8. Prepare for the audit itself by selecting the date for performing it, and schedule it for that date with the various parties involved (your boss, the operating staff, etc.). Typically, audits are performed while the unit or source is in service and operating.
9. Assemble whatever other supplies you need to perform the audit. This might include, but it is not limited to:
a. Audit check list or an in-house procedure
b. Whatever notes you need to use to perform a CGA

Day of Audit Activities

10. Review your in-house audit procedure, making sure you understand it and can answer questions from those whom you will work or interface with.
11. Confirm with the other parties involved that the audit can proceed today and that the unit is scheduled to operate long enough to complete the audit.
12. The audit should only be performed after successfully completing the daily calibration check.
13. When you are ready to begin, contact the control room operator and tell them you are beginning and ask if you can have steady operating conditions until you are done. Make them aware that they may see the CEMs reading jumping around as you perform the audit.


14. A successful CGA is completed by running two different sets of blended gases through the system three separate times. Each set of gases will have a:
a. Low concentration (20-30% of span value) for NOx and SO2, or 5 - 8% by volume for CO2 or 4 – 6% by volume for O2, and
b. Mid concentration (50-60% of span value) for NOx and SO2, or 10 - 14% by volume for CO2 or 8 – 12% by volume for O2,
c. The average of the readings recorded while flowing the low concentration is compared against the audit value for the low cylinders. The average of the mid readings is compared against the audit value for the mid cylinder.
d. The audit results are unacceptable if the accuracy recorded is ±15% of the average audit value or ±5 ppm, whichever is greater. Note: the limit of ±5 ppm is generally considered to be the alternate standard for an CGA. [Section 5.2.3 (2)]
15. Once you begin, and until the last or sixth run is recorded, no adjustments are allowed to the monitors. If any adjustment is necessary, then the audit for that monitor is generally considered to be aborted and an aborted audit is considered to be a failed audit.
16. Start each run of the gases after the data system has recorded minute data in the first two clock quadrants. A properly executed audit can be successfully completed in three hours, and still have valid hourly averages based on collecting two data points per hour during a QA check.
17. When the audit is over, review the system while you are still in the shelter and make sure it has been restored to normal operating status. Make sure the gas cylinders are set up and valved in for a successful calibration check in the next morning.

When you are done – Wrapping It Up

18. Take your notes from the audit and setup your CGA records in the Linearity/CGA editor of StackVision. In SV, at the Main Menu, select “Tools → QA and Certification → Linearity/CGA”.  Make sure the editor says that you have “Passed”. Click on the Locked? Box.  Save the CGA records.
19. Some facilities have separate Linearity and CGA records for the same monitors. If your facility is one of these types, be sure to setup separate auditing records according to your in-house procedure.
20. Make a note of how much pressure remains in the cylinders for the next round of audits.  If any cylinder has less than 500 psi, it’s time to verify that you have a replacement cylinder in hand. If none are available, then order at least two more sets of cylinders. 
21. Remember, linking the gas certificates for a CGA under P60 is not necessary.
22. Remember that CGA records for SO2, NOx, CO2, O2 or CO are not to be included in QA EDR files. 

Download the pdf document here.

Jon Konings, Senior Regulatory and Reporting Engineer, ESC    Published: 9/21/2016 5:10:39 PM

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