Laser velocimeter measurements were made to quantify the mixing between a simulated roof layer and ventilation air in a model mine. A model mine was built and the effect of the following were measured: reynolds number, richardson number, air speed, layer thickness, gas density, turbulence intensity, and mixing length. A turbulence model was used to explain the data. Increasing the reynolds number promoted mixing, causing vortices to break down into more efficient, fine-scaled turbulence. Decreasing the richardson number also promoted mixing; richardson numbers less than 0.3 Resulted in complete mixing. Turbulence intensity increased as the richardson number decreased. The velocimeter system was assembled and made operational for methane roof layer studies in the Bruceton Experimental Mine. Engineering drawings were provided and optics were aligned. Computer programs for data acquisition and an instruction manual were also provided.