Relative Accuracy Test Audits (RATAs) are essential for ensuring that mercury monitoring systems are functioning correctly and reporting accurate data. However, many facilities run into unnecessary complications due to persistent misunderstandings, particularly when it comes to PS 12B sorbent trap RATAs. Missteps here can lead to costly repeat testing or invalidated results.
To help you stay on track, we’ve compiled several common misconceptions we frequently encounter, along with clarifications based directly on regulatory language.
Misconception: I have to use full-sized PS 12B traps during the RATA.
Some customers have asked us how it’s possible to achieve a 1 LPM sampling flow rate during a RATA when using 450 mm PS 12B traps with extended sections and acid gas scrubbers. In many cases, they’ve found that even reaching 500 cc/min can lead to a high vacuum, raising concerns about system performance during the audit. The good news is, according to PS 12B, smaller RATA-specific traps are not only acceptable, they’re recommended:
“Section 8.3.2 Special Considerations. The type of sorbent material used in the traps must be the same as that used for daily operation of the monitoring system; however, the size of the traps used for the RA test may be smaller than the traps used for daily operation of the system.”
These smaller PS 12B RATA traps are specifically designed to allow proper flow rates and system operation during the audit. Additionally, upon request, RATA traps can be configured with smaller AGS sections to match your routine weekly configuration while still complying with the specification.
Misconception: My traps show >5% breakthrough in section 2 – is that an automatic fail?
We’ve also heard from customers concerned about breakthrough levels on PS 12B RATA traps. For example, when section 1 contains only 10 ng of mercury and section 2 contains 1 ng, this results in a 10% breakthrough, exceeding the ≤5% threshold specified in PS 12B. Situations like this can make it challenging to meet standard breakthrough criteria, especially at low mercury concentrations.
Fortunately for you, according to Appendix A to Subpart UUUUU of 40 CFR Part 63 – Hg Monitoring Provisions:
4.1.2.2 The special considerations specified in paragraph 4.1.1.5.1 of this section apply to the RATA of a sorbent trap monitoring system. During the RATA, the monitoring system must be operated and quality-assured in accordance with Performance Specification (PS) 12B in Appendix B to part 60 of this chapter with the following exceptions for sorbent trap section 2 breakthrough:
4.1.2.2.1 For stack Hg concentrations >1 μg/dscm, ≤ 10% of section 1 Hg mass;
4.1.2.2.2 For stack Hg concentrations ≤1 μg/dscm and >0.5 μg/dscm, ≤ 20% of section 1 Hg mass;
4.1.2.2.3 For stack Hg concentrations ≤0.5 μg/dscm and >0.1 μg/dscm, ≤ 50% of section 1 Hg mass; and
4.1.2.2.4 For stack Hg concentrations ≤ 0.1μg/dscm, no breakthrough criterion assuming all other QA/QC specifications are met.
This concentration-based approach provides much-needed flexibility, especially for facilities operating at low emission levels.
Misconception: A failed second source calibration standard means I can proceed anyway.
In some cases, customers have reported that their independent calibration standard (also known as the second source standard) did not meet the required ±10% acceptance criteria. This raises an important question: can analysis proceed under these circumstances?
In short, we recommend pausing your analysis and doing some recalibration, as this failure could be due to an expired or evaporated low-level standard, or even a leak in the analyzer. We strongly recommend running an analysis audit sample following re-calibration to ensure there are no system integrity issues. If you need guidance on how to do this, feel free to contact us; we’d be happy to provide some suggestions.
Misconception: Forgetting a CCVS invalidates the RATA.
While we do strongly recommend completing a CCVS (Continuing Calibration Verification Standard) after each set of PS 12B sorbent traps, unlike for 30B it’s not a requirement. If you are analyzing both PS 12B and 30B traps on the same analyzer, we recommend performing a CCVS after each set of 30B traps.
Misconception: A failed CCVS means the entire RATA must be redone.
Some users have asked what to do when a Continuing Calibration Verification Standard (CCVS) result falls outside the ±10% acceptance range. Does this mean the entire RATA must be discarded?
Not necessarily. In this case, the instrument must be re-calibrated, and the independent standard analysis repeated. This is one reason Ohio Lumex recommends performing a CCVS after each set of traps – it limits the scope of any necessary retesting. Only the samples analyzed before the failed CCVS are invalidated; if the most recent CCVS passes, then all traps analyzed after that point remain valid.
This requirement applies specifically to Method 30B sorbent traps. Any invalidated runs must be repeated. To minimize disruption, incorporating an audit sample can help confirm system integrity and rule out potential issues such as leaks, or less likely, accidental contamination from something as simple as a spilled beverage near the analyzer.
Final Thoughts
A successful RATA doesn’t have to be stressful. By understanding the current regulatory flexibility and being consistent in your materials and procedures, you can avoid common mistakes that cost time and money.
Need help preparing for your next RATA? Ohio Lumex offers custom RATA traps (Method 30B, Method PS12B), expert guidance, and dependable sorbent trap support to ensure your compliance strategy stays on track.
We also offer a full range of services to make the process even easier:
- Our experienced On-Site Analytical Team can handle the entire RATA analysis process on-site, ensuring accuracy, consistency, and regulatory compliance from start to finish.
- Prefer to collect your own samples? Our fully staffed, in-house Analytical Laboratory is ready to handle your trap analysis with fast turnaround times and reliable results.
Contact us to find out how we can help simplify your RATA process and support your compliance goals.
