One of the key problems in coping with deliberate or accidental atmospheric releases is the ability to reliably predict the individual exposure during the event. Furthermore, for the implementation of countermeasures, it is essential to predict the maximum expected dosage and the exposure time within which the dosage exceeds certain health limits. Current state of the art methods, which are based on the concentration cumulative distribution function (cdf) and require the knowledge of the concentration variance and the intermittency factor, have certain limitations especially when the exposure time becomes comparable with the peak spectral time. The proposed method aims at estimating maximum dosage as a function of the exposure time, mean concentration and the turbulence integral time scale. It is much simpler than the cdf models and it poses no restrictions on the exposure time length. One of the important consequences is that it can broaden the capability of the ensemble average computational models to estimate maximum dosage for any exposure time. The method has been tested successfully utilizing the ammonia field experiments FLADIS T16 and T17.