A simple method of predicting the tritium concentration in air leaving an atmospheric-detritiation dryer (ADD) was developed and compared to experimental data. The prediction method was developed for use with closed-loop regenerated, thermal-swing dryers by extending the constant-pattern method for analyzing desiccant dehumidifiers. Tests were carried out at tritium activities up to 3 500 GBq/kg. For ADDs filled with commercial, zeolite desiccants, it was found that the prediction method provided a reasonable worst-case estimate of the tritium concentration (Bq/m3) exiting a dryer during adsorption.