The adsorption and penetration behaviour of 23 organic vapours on an activated carbon bed were studied varying the flow rate of the vapours (V = 0.2, 0.4, 0.81 cm - 2 -minute) and the bed depth (Z = 1.0, 2.0 cm). An improved equation for predicting breakthrough time of organic vapours and dry air mixture was proposed which provides a high level of accuracy.