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Research Triangle Park NC 27711
Research and Development
EPA-600/S4-81 -080 Dec. 1981
Project Summary
Analysis of Commercial
Cylinder Gases of Nitric Oxide,
Sulfur Dioxide, and Carbon
Monoxide at Source
Concentrations—Results of
Audit 5
C. E. Decker, W. C. Eaton, R. C. Shores, C. V. Wall
The U.S. Environmental Protection
Agency (EPA) has established a
national performance audit program
to determine the accuracy of analyses
of cylinder gases supplied by com-
mercial gas manufacturers. As of June
1981, five audits have been per-
formed on 14 individual suppliers.
Audit 1 was performed in June 1978,
Audits 2 and 3 in January and
September 1979. Audit 4 in April
1980, and Audit 5 in March-June
1981. To ensure that manufacturers
would not give preferential treatment
to EPA in providing the gases, EPA
obtained cylinder gases for all audits
through an anonymous third party.
Audits 1 through 5 include cylinders
of sulfur dioxide (90 and 500 ppm),
nitric oxide (50 and 300 ppm), and
carbon monoxide (50 and 500 ppm).
Cylinder gases were analyzed by
Research Triangle Institute (RTI)
according to EPA's "Traceability
Protocol for Establishing True Con-
centrations of Gases Used for Calibra-
tion and Audits of Continuous
Emission Monitors" (Protocol 1, June
15, 1978). Internal quality control
procedures by RTI and external quality
assurance performance audits by EPA
prior to each audit are important
elements of the Quality Assurance
Plan. Results of Audit 5 and a
summary of results for all five per-
formance audits are presented for
each manufacturer included in the
audit program.
This Project Summary was develop-
ed by EPA's Environmental Sciences
Research Laboratory, Research Tri-
angle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
High quality gas standards must be
used for calibration and auditing of
ambient air and source emissions
monitors. Manufacturers of commercial
cylinder gas supply gas standards with a
certified analysis and statement of
accuracy. Generally, the level of accur-
acy is specified as a percentage of the
component value. To ascertain the
accuracy of analyses of commercially
available cylinder gases, the U.S.
Environmental Protection Agency (EPA)
has initiated a national performance
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audit program of commercial gas manu-
facturers. In June 1981, Audit 5 of this
program was completed. Audit 1 was
performed in June 1978, Audits 2 and 3
in January and September 1979, and
Audit 4 in April 1980. Results of these
audits are documented in separate
reports that are available from the EPA
Project Officer.
Audit 5 was conducted from March to
June 1981 to analyze the concentration
of cylinder gases purchased from a
representative sample of manufacturers
and to determine the accuracy of the
manufacturers' certified concentrations
Audit 5 included cylinders of sulfur
dioxide at 90 and 500 ppm, nitric oxide
at 50 and 300 ppm, and carbon
monoxide at 50 and 500 ppm obtained
from 14 different manufacturers. In
order to ensure that suppliers would not
give preferential treatment to EPA in
providing the gases, EPA obtained
cylinder gases for Audit 5 through an
anonymous third party. Specifications
of the type of analysis or the type of
cylinder (steel or aluminum) were not
included on the purchase request. The
only specifications given to the manu-
facturers were cylinder size,
components, nominal concentration
levels, and a request for a certified
analysis. The request for a certified
analysis did not specify that manufac-
turers should analyze cylinder gases
according to the EPA's Traceability
Protocol No. 1.
Procedure
Cylinders of gas procured for Audit 5
were analyzed by RTI using source
emission analyzers, according to EPA's
Traceability Protocol No. 1. National
Bureau of Standards-Standard Refer-
ence Materials (NBS-SRM's) were used
to generate gas concentrations for cali-
bration of the source emission
analyzers, as specified in Protocol No. 1.
Each cylinder gas was analyzed three
times with an NBS-SRM (gas standard)
or Gas Manufacturers Primary
Standard (GMPS) being introduced
between analyses as a control check on
the analyzer. A strict internal quality
control program was maintained during
Audit 5. Prior to the audit, an external
quality assurance performance audit
was conducted by EPA on the organiza-
tion performing the audit (RTI). Agree-
ment to within ±3 percent was required
between RTI and EPA before the audit
could begin. In addition, EPA provided a
confirmatory analysis of any cylinder
gas where the percent accuracy
between the manufacturers' analysis
and the mean-of the auditor's analysis
varied by more than 4 percent.
Summary of Results
The results of Audit 5 are given in
Tables 5 through 7 of the full report.
Each table includes the manufacturer's
name, cylinder type, manufacturer's
analysis, mean of theauditor'sanalysis,
EPA confirmatory analysis (if required),
parts-per-million difference, and
percent accuracy. The audit results
show that for 26 cylinders of sulfur
dioxide, 9 cylinders had inaccuracies of
>10 percent; 5 of the 9 cylinders had
inaccuracies of >30 percent, and 1 of
the 5 cylinders had an inaccuracy of
>100 percent. Results for nitric oxide
and carbon monoxide were substantial-
ly better than those for sulfur dioxide: of
28 nitric oxide cylinder gases, 2 had
inaccuracies between 10 and 20
percent; of 28 carbon monoxide cylinder
gases, 4 had inaccuracies between 10
and 20 percent; the remaining nitric
oxide and carbon monoxide cylinder
gases had inaccuracies of <10 percent.
Conclusion
High quality gas standards must be
used by organizations performing
ambient air monitoring, source emis-
sion monitoring, and research studies.
The results of Audit 5 show the need for
improvement in the quality of cylinder
gases available from commercial manu-
facturers.
Recommendations
Based on the results of Audit 5, it is
recommended that audits of
commercial cylinder gas manufacturers
be continued on a routine basis. Future
monitoring programs should define the
need to include additional gases besides
sulfur dioxide, nitric oxide, and carbon
monoxide in the national performance
audit.
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C. E. Decker, W. C. Eaton, R. C. Shores, andC. V. Wall are with Research Triangle
Institute, Research Triangle Park, NC 27709.
D. J. von Lehmden is the EPA Project Officer (see below).
The complete report, entitled "Analysis of Commercial Cylinder Gases of NO,
SO2 and CO at Source Concentrations: Results of Audit 5," (Order No.
PB 82-118 654; Cost: $6.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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Fees Paid
Environmental
Protection
Agency
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Penalty for Private Use $300
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