Dismantling and decommissioning operation of three glove boxes contaminated by 241Am was conducted in summer 2001. During the first two terms of the decommissioning project no hesitation appeared about the adequacy of the protective regime. After measuring of filters from ventilation during the third term the volume activity was assessed as 1.5 Bq/m3 with the volume of filtered air of 69.2 m3 at a flow rate of 1 m3 per hour and all the working activities were stopped. On the basis of first results, six workers were treated with calcium trisodium diethylene-triamine-pentaacetate (Ca-DTPA) in infusions. The check of urine proved the increased excretion of contaminating radionuclide. The tolerance of the treatment was good. Final evaluation based on complex excretion data in the workers pointed to the committed effective dose of 35–185 mSv. This extraordinary event was caused first of all by the considerable underestimation of the hazard of the dismantling of dry glove boxes.