40 CFR 92.112 - Analytical gases.
(a) Gases for the CO and CO2 analyzers shall be single blends of CO and CO2, respectively, using zero grade nitrogen as the diluent.
(b) Gases for the hydrocarbon analyzer shall be single blends of propane using zero grade air as the diluent.
(c) Gases for the methane analyzer shall be single blends of methane using air as the diluent.
(d) Gases for the NOX analyzer shall be single blends of NO named as NOX with a maximum NO2 concentration of 5 percent of the nominal value using zero grade nitrogen as the diluent.
(e) Fuel for the HFID (or FID, as applicable) and the methane analyzer shall be a blend of 40±2 percent hydrogen with the balance being helium. The mixture shall contain less than 1 ppm equivalent carbon response; 98 to 100 percent hydrogen fuel may be used with advance approval of the Administrator.
(f)Hydrocarbon analyzer burner air. The concentration of oxygen must be within 1 mole percent of the oxygen concentration of the burner air used in the latest oxygen interference check (%O2I). If the difference in oxygen concentration is greater than 1 mole percent, then the oxygen interference must be checked and the analyzer adjusted if necessary, to meet the %O2I requirements. The burner air must contain less than 2 ppmC hydrocarbon.
(g) The allowable zero gas (air or nitrogen) impurity concentrations shall not exceed 1 ppm equivalent carbon response, 1 ppm carbon monoxide, 0.04 percent (400 ppm) carbon dioxide and 0.1 ppm nitric oxide.
(1) “Zero-grade air” includes artificial “air” consisting of a blend of nitrogen and oxygen with oxygen concentrations between 18 and 21 mole percent.
(i) Oxygen interference check gases shall contain propane at a concentration greater than 50 percent of range. The concentration value shall be determined to calibration gas tolerances by chromatographic analysis of total hydrocarbons plus impurities or by dynamic blending. Nitrogen shall be the predominant diluent with the balance being oxygen. Oxygen concentration in the diluent shall be between 20 and 22 percent.
(j) The use of precision blending devices (gas dividers) to obtain the required calibration gas concentrations is acceptable, provided that the blended gases are accurate to within ±1.5 percent of NIST gas standards, or other gas standards which have been approved by the Administrator. This accuracy implies that primary gases used for blending must be “named” to an accuracy of at least ±1 percent, traceable to NIST or other approved gas standards.