The paper describes the development of a screening technique to determine the maximum 1 hour ground level concentration of a gaseous emission from a stack located in flat terrain. The method does not require the use of a computer and eliminates the usual trial and error calculations. An infinite mixing height is assumed. It involves a linear or quadratic solution of the gaussian plume diffusion as a function of the effective stack height and a linear approximation of the Briggs plume rise equation. The linear approximation of the former gives results that are within 5% of the gaussian plume results for stability criteria A, B, and C. For stability criterion D, the difference can be as great as 80%. If a quadratic estimation is used, the differences are less than 3% for stability criteria A, B, and C, and are within 18% for stability criterion D. A linear approximation is used for the Briggs plume rise equation. This gives results within 4% of the Briggs equation. Overall, this is a simple straightforward approximation which gives results which can be used to determine if more sophisticated procedures are necessary.