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10 Things to Know About Gas EPA Protocol
Dated: 9 Oct 2007
10 Things to Know About Gas

Posted: September 5

Having information about proper planning and handling of protocol gases could potentially save significant dollars. Here are a few very important points to consider for those that need to calibrate important sensors.

The proper handling of protocol gases and calibration of test equipment and sensors are extremely important. The results can avoid incalculable headaches and costs.

In the wake of the recent changes to 40 CFR Part 60 test methods, there are many things businesses can do to prevent problems with their calibration gases. Here are features ten key tips to help ensure accuracy and stability of protocol gases.

1. Review the EPA list of approved Protocol Gas Verification Program vendors. The EPA will be creating a list of companies that participate in the new Protocol Gas Verification Program (PGVP), which will be required under 40 CFR Part 75 section 5.1.1 of Appendix A (the final Part 75 rule is expected to be published November 2007). Participation in the PGVP is already a requirement in CFR 40 part 58 Appendix A sections 2.6.1. The results of the PGVP and the list of approved vendors will be posted to the agencys site, so businesses can check to see whether its gas vendor is participating in the program.

2. Make sure that your gases are within the expiration dates. Gases, like medicines, have a definitive shelf life. The maximum shelf life for any EPA protocol gas mixture is defined within the most current EPA traceability protocol guidelines as ranging from six to 36 months. Using an expired EPA protocol gas for a test will result in noncompliance with permit conditions, and, as a result, the gas will have to be recertified. An expired gas that has less than 500 psi (1/4 tank), cannot legally be recertified, so pay attention to those expiration dates!

3. Ask the vendor to make gases directly traceable to NIST or NMi gases. Although gas vendors legally can create gases that trace from Gas Measurement Instrument Standards (GMIS), there is more uncertainty associated with them. Since daily, quarterly and Relative Accuracy Test Audit (RATA) monitoring is directly affected by the quality of the EPA protocol gases used, it is beneficial to use mixtures with the highest possible accuracy. Gases directly traceable from National Institute of Standards and Technology (NIST), or another national measurement institute (NMi), reduce the uncertainty of the accuracy of the gas cylinders contents.

4. Tour the facility producing the protocol gases. Vendors that make EPA protocol gases using the same processes for industrial gas products may not be providing the most accurate results. This is because EPA protocol gases should be created using special testing methodologies, instrumentation calibration, data recording, traceability and stability.

When touring a vendors facility, it is important to learn which analyzers the vendor uses, how instrument calibration is performed, how frequently such calibration is performed, how curve fitting data and analytical triads are statistically evaluated, and how interferences between gases are accounted. Additionally, end users should ask to see the vendors stock of traceable gases: GMISs, standard reference materials (SRM), NIST traceable reference materials (NTRM) and primary reference materials (PRM). Be sure to find out if the gas manufacturer is working on any new reference materials and testing procedures to stay current with new regulations. Also, ask if the vendor picks up and delivers the cylinders. This is a great time saver and assures compliance with all DOT regulations for shipping and handling cylinders for the end users.

5. Use non-permeable stainless steel lines or vent the lines with nitrogen for SO2 EPA protocol gases. SO2 has an extremely strong affinity for water molecules and is able to draw outside moisture through Teflon and vinyl tubing. For those flowing SO2 through vinyl or Teflon, moisture diffusion can occur and subsequently produce a caustic solution in the lines. Installing stainless steel lines or venting the stagnant sampling lines with nitrogen will quickly eliminate moisture contamination.

6. Ensure emissions auditors use the same gas mixture type used in-house for daily and RATA calibrations. Problems can occur if auditors do not use the same gas mixture as is used for internal auditing. Using two different types of cylinders with varying components or concentrations of CO2 will change the reported NOX value. This could cause conflicting NOX reports in annual RATA tests or audits possibly leading to test failures. To eliminate such problems, make sure the mixtures, number of components and concentrations are the same.

7. Store protocol gases at above freezing temperatures. Protocol gases containing CO2 should be stored and used at temperatures above freezing to avoid stratification problems. If using a mercury cylinder, be sure to keep the temperature constant or risk ruining the ppm value of the concentration. Carefully bring cylinders from temperatures below freezing to warmer temperatures and roll the cylinder to mix the gases. Also, do not open a valve when a cylinder is cold or its contents will stratify. Keep cylinders inside a warming shelter or use cylinder blankets to avoid these problems.

Protocol gases are used to calibrate a variety of testing equipment. It is very important that all gas cylinders be securely stored, even when not in use as shown above. The photograph was supplied courtesy of Airgas Inc.

8. Carefully remove air contamination from CEM station lines when using low-level ppm NO protocol gases. Check that all Teflon O-rings are both usable and undamaged. Evacuate the lines, and quickly open and close the cylinder valve as a pre-fill/drain process. Repeat this process three times. An alternative method is to use a dual-stage regulator so the cylinder can be shut off before the gas gets to the stainless steel lines when changing the cylinders and make sure the valves are in the open position when venting a low-level ppm NO gas to avoid gas getting into the cylinder or the line. Turn off the gas at the cylinder before turning off gas valves in the lines. Even a small amount of moisture in the cylinder will ruin the ppm value of the NO. Taking these precautions can save thousands of dollars in cylinder costs, and ultimately millions in terms of incorrect emissions reporting and maintaining compliance with the Title V air permit.

9. Seek gases within the compliant range when running low on protocol gas or facing an emergency. Emergencies arise when gas is immediately needed and exact substitute values for emissions are not instantly available. For this reason, it is vital to know the range of gas that can be used to maintain compliance. A gas that fits in the applications range and meets compliance regulations can be provided in the interim and is significantly less expensive than ordering the exact concentration.

10. Do not let the stack tester order the protocol gas. Environmental consultants sometimes include marked-up gas prices in their stack testing contracts. Businesses can query their stack testers to provide advance notice of what to purchase, and then purchase the gases from its own vendor. Such gases are needed for daily calibration/quarterly linearities after yearly tests are over. If gas ranges remain high enough, the same gases will be needed for use in the next years test resulting in several hundred dollars in savings.

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