Method Sensitivity (leak rate in mbar l/s) Ultrasonics 10−1 Bubble test in water 10−2 Pressure decay 10−2 Vacuum decay 10−2 Acoustic emission detectors 10−3 Bubble test in soapy water 10−4 Gas-specific thermal conductivity detector 10−5 Halogen detector 10−5 Photoacoustic spectroscopy 10−6 Hydrogen sniffer 10−6 Residual gas analyser 10−7 Dye penetrant 10−8 Radioactive tracer 10−10 Helium mass spectrometry vacuum testing 10−11