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EPA Protocol Revisions – Traceability for Gaseous Calibration Standards

1. Include a procedure specifically for the use of Fourier Transform infrared 

Spectroscopy:

The current document’s purpose is to provide traceability and ensure accuracy of the analysis. 

It is not designed to provide detailed instructions on doing the analysis on a specific analyzer. 

If FTIR were to be added, then various GC detectors and other process analyzers would need 

to be added making the document cumbersome and limiting the new technology that could be 

used.

2. Improve statistical procedures for uncertainty calculations and revise the Excel 

spreadsheet:

We see no real reason for changing the statistical calculations and the Excel spreadsheet. In 

fact, there are numerous other acceptable methods for calculating total uncertainty that could 

be used. 

3. Include mercury calibration standards in the protocol: 

There appears to be no reason to specifically add Mercury to Table 2-3 or create a special 

section for mercury or any other compound. However a footnote for Table 2-3 that makes it 

clear that the components listed are not the only ones that can be made as EPA Protocols. As 

long as new traceable standards exist, and the protocol can be followed, then a component 

can be called an EPA Protocol. 

4. Eliminate (or retain) gas manufacturers intermediate standards (GMISs):

The purpose of the EPA protocol is to ensure accuracy and traceability. Changes that should 

be considered should help improve these two aspects. GMISs are standards that are 

unverified by EPA or NIST and as such are suspect. In fact they are made using a similar 

methodology to making EPA Protocol mixes, so if a company cannot accurately make 

protocols, then it is likely that they will have significant errors in their GMISs that will carry

over to samples that they analyze. Even using the best of techniques, the uncertainty of the 

GMIS has to be greater than that of the SRMs, NTRMs, or PRMs due to the propagation of 

error. As a result of these two issues, using GMISs inherently is less accurate and invites 

problems. Using the verified metrology standards is the best guarantee for eliminating or 

minimizing the uncertainty contribution from the reference standards.

5. Lengthen the certification periods for EPA Protocol Gases:

The current expiration dates are valid from the perspective of stability and use. Most users 

will run out of gas in about 18 months, so the 24 and 36 months expiration periods for stable 

components are sufficient. In regard to reactive components at low concentrations, increasing 
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the expiration dates runs the risk of failure due to instability, which was not identified during 

the 2 required triad analyses. The rate of reaction typically slows as the concentration of the 

reactive component decreases, leading to the potential for component instability. The 

requirement to recertify these mixtures after the initial 6-month period is designed to prevent 

long-term stability problems in the field.

6. Change the cylinder pressure limitations for EPA Protocol Gases:

We see this as a two-part issue. We believe the limit of 150 psig, below which the Protocol 

cannot be used, should remain unchanged. We have seen instances where wall effects in the 

cylinder resulted in concentration changes at low pressure.

The second part of the issue relates to the 500 psig limit for recertification of mixtures. We 

agree with lowering that limit, but certainly no lower than 150 psig. There are instances, 

where a Protocol has expired while in use, and being able to recertify it helps the end user 

with the state or federal agency that monitors that facility.

7. Include a procedure for analyzing and certifying zero gases:

There are no trace standards currently available from NIST to analyze most of the 

contaminants of interest. These would have to be developed in conjunction with any specific 

procedure for analyzing and certifying these types of gases. Currently, some manufacturers 

do not specifically analyze the zero gases for individual impurities, and just “assume” that 

they are clean, and of course, this is not always the case. This may be more involved than 

initially thought and perhaps should be an addendum to the protocol. Otherwise we are in 

favor of this.

8. Include gas dilution systems in the protocol: 

The G2 protocol includes mention of dilution. If the suggestion is to add specifics on what 

specific types of systems/ devices can be used and how they are to be used, we feel this 

would be too restrictive and beyond the scope of the intent of the protocol.

9. Tighten documentation requirements: 

Field verification of conformance of a calibration gas mixture to the protocol is an important 

compliance tool.

In order to facilitate calibration gas verification, a full disclosure certification should include: 

1. Cylinder identification number

2. Certified minor component concentration(s)

3. Balance gas

4. Cylinder pressure at time of certification

5. Assay / certification date
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6. Certification expiration date

7. Reference standard identification (standard number, cylinder number, minor 

component concentration, expiration date)

8. Statement that the assay / certification conforms to EPA Protocol guidelines

9. Analytical methodology used for certification

10. Laboratory identification (name, address, telephone number)

11. Record of previous EPA protocol gas certification

12. Analytical accuracy for each certified minor component

13. Statement that the certified concentration has been corrected for interference, if 

applicable.

14. Analyzer identification (make, model, serial number, measurement principle, and 

last multi-point calibration date)

15. All triad analyzer readings used to obtain the certified minor component 

concentration(s)

16. Correlation coefficient and calibration curve equation used to calculate the 

certified minor component concentration(s).

17. Specific Total Oxides of Nitrogen reference value for all Nitric Oxide protocol gas 

cylinders.

Having all this information will allow end users as well as auditors/ inspectors to more 

readily identify where expired standards were used, falsification of the ZRT Triad analysis, 

inappropriate analyzers used for analysis without addressing interference issues, as well as 

independent verification of the mathematics used to calculate the concentrations against a 

curve.

10. Develop audit participant identification number for regulatory data reporting 

purposes:

There is no value in regard to strengthening the purpose and intent of the existing protocol, as 

the manufacturer’s contact information is already on the Certificate of analysis.

11. Require ISO 17025 accreditation for producers of environmental calibration gases:

ISO 17025 is an extremely expensive certification and does not guarantee that a better 

protocol product will be manufactured. In fact, a gas manufacturer, holding certification to 

the ISO 17025 standard, registered at least 1 failure in the recent blind audit. The high cost of 

accreditation to the ISO 17025 standard would create an economic inequity among gas 

manufacturers, creating a competitive advantage favoring large manufacturers.

Technically, one of the core concepts of the ISO 17025 standard is the manner by which 

uncertainty is propagated. In order to assert accreditation of a laboratory to the ISO 17025 

standard as a requirement, the protocol would need to be changed so the calculation of 

uncertainty would match the conventions dictated by ISO 17025. As previously stated (see 

item 2), we do not view this as a valuable change to the existing protocol.
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12. Include provision for preparation and analysis of batches of EPA Protocol gases:

Batch analysis of protocol mixes does not move us in the direction of making better product. 

It will reduce costs but expose the customer to possible problems that can and will occur 

since homogeneity is not guaranteed. NIST has seen problems of homogeneity with batch 

preparation of SRMs, and those same problems occur when preparing Protocols. In fact, the 

problems will be greater since many protocols are now multicomponent mixtures, and 

homogeneity is more difficult than with a single component Protocol.

As an aside, some producers analyze NOx in NO Protocol mixes on a batch basis, which is 

erroneous. Scott recommends that EPA require that NOx values that are assigned to NO 

protocol gas mixtures be actual values and not batch values since end users need to know the 

actual NOx value for each cylinder of NO Protocol.

13. Require on-site visits of specialty gas producers by EPA representatives:

This would provide no value to the end users. A producer would do the “right” things if and 

when an audit would occur, and the costs would be prohibitive. Better to spend the resources 

of EPA auditing end users, and if problems are found there, test those protocols that are 

questionable.

14. Provide for technical assistance/outreach to specialty gas producers by NIST 

representatives:

This should not be part of the protocol. Any gas company can approach NIST with questions 

regarding product production, whether it is related to protocols or not. At the same time, 

having NIST and/or EPA auditing gas producers opens up the possibility of the auditors 

passing on technical suggestions for improvement that originate in one producer and would 

provide an advantage to a competitor.