Recognizing the potential problems associated with the proliferation of new chemicals, Congress passed the Toxic Substances Control Act (PL94-469) (TSCA) in 1976. The Act establishes EPA's authority to regulate, if necessary, all commercial chemicals before they are commercialized. Effective July 1, 1979, section 5 of TSCA requires persons to notify EPA through the submission of a Premanufacturing Notice (PMN) at least ninety days before the manufacture or import of a chemical not on the 'Inventory' of existing chemical substances. Since a new 'PMN chemical' has not been commercialized, potential exposures and releases resulting from the manufacture, processing and/or use of the chemical must be estimated based on minimum data. The concept of 'unit operations' has been proposed for the evaluation of such potentials. Predictive models are being developed to identify possible sources of chemical releases and points of potential worker exposure from several unit operations. Input variables for these models include the physical properties of the chemical substance and the operational specifications of the unit operation.