The manual gives instructions for using Controlling Air Toxics (CAT). The primary objective of this interactive and user-friendly software package is to assist in the review of air emission permit applications. The engineering software is based on the EPA document, Control Technologies for Hazardous Air Pollutants, EPA/625/6-86/014, September 1986. The software is written for the IBM PC using the Microsoft V3.0 C compiler and Windows for Data Library V1.0 for screen and keyboard interaction. The permit reviewer can input information on the air emission stream characteristics as well as other information in the permit application. The program provides guidance on which control devices may be appropriate and allows the reviewer to select a specific pollutant/control device combination for evaluation. The control devices included in the program are thermal and catalytic incinerators, flares, carbon adsorbers, absorbers, condensers, fabric filters, and venturi scrubbers. The program then calculates design parameters and estimates costs for each control device selected. The results can be compared against the permit applicant's actual or proposed design.