A method based on studies of model filters is suggested for prediction of breakthrough times and capacities of activated carbon filters in local exhaust ventilation units. Toluene was used as the test substance. The method involves the determination of three penetration curve parameters from testing of the model filters. The penetration curve parameters are subsequently used in combination with a suitable predictive equation for calculating breakthrough times of large-scale filters containing different amounts of activated carbon. The results indicate that the filter under investigation will have a relatively short breakthrough time under normal working conditions and it is recommended that the amount of activated carbon should be substantially increased.