The pulsation of small-scale ethyl alcohol pool fires has been examined using high speed imaging techniques, and a method for determining pulsation frequency by analyzing the temporal fluctuation of RGB image components is presented. Using this method, pulsation rates for six different ethyl alcohol pool fires ranging from 30 to 125 mm in diameter were found to be in good agreement with existing experiments. Based on experimental results, a new physical model to explain the mechanism of fire pulsation is developed. This model describes the development of "thermals,'' or isolated structures of strong local buoyancy, as the primary cause of oscillatory behavior in pool fires.