sentences:  One thing to be aware of when operating a TCD is that gas flow must never be interrupted when the filament is hot, as doing so may cause the filament to burn out.While the filament of a TCD is generally chemically passivated to prevent it from reacting with oxygen, the passivation layer can be attacked by halogenated compounds, so these should be avoided wherever possible.If analyzing for hydrogen, the peak will appear as negative when helium is used as the reference gas.