These projects document the correlation of precise laboratory leak rate measurements with the EPA Method 21 protocol for PPMV (parts per million by volume) measurements with Helium and Methane using the standard bagging technique. An instrumented NPS 4 class 600 bolted joint fixture with a flexible graphite sheet gasket was used. Large to very low flow rates in Helium and Methane were investigated with the gasket subjected to a stress range of 1000 to 15000 psi (8. to 103 MPa) gasket stress and pressures from 50 to 800 psi (0.35 to 8.5Mpa). Concluding that the standard EPA bagging method is accurate for PPMV emission measurements, the authors also question sniffing around a flange in an open environment as a reliable method of emissions measurement. More important to plant engineers is confirming the reliability of EPA Method 21 flow formula as a means to compare field PPMV measurements with reported laboratory leakage results as an aid to gasket selection.