This paper reports the development of a gas sampling and static reactor system for identifying potentially toxic volatile byproducts from an industrial process and for characterizing their airborne stability at trace levels. The system has been applied in an exemplary manner to the analysis and fate of diborane and phosphine. The heart of the system consists of a static reactor to which pyrolysis products or other reactants can be added from a flow reactor. The static reactor can be resampled at any time. Methods for identifying and quantifying pyrolysis products by chromatography with multiple detectors and mass spectroscopy are included.