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The arsenic concentrate was used in the production of high-purity zinc (99.99%) according to hydrometallurgical process. This study analyzed arsenic concentrate from the former Lojane mine in North Macedonia, which was used in the chemical industry Zorka Šabac, Serbia. The activity concentrations of 226Ra in 15 samples of arsenic concentrate, which were necessary for assessing indoor radon concentration, were determined using gamma spectrometry. The average value was around 200 Bq kg-1. To assess indoor radon concentration for workers in the warehouse, the radon mass exhalation rate was measured, given that the material is powdery. The RAD7 device was used to determine radon mass exhalation. Based on the obtained values, indoor radon values to which workers were potentially exposed were estimated. Considering that the warehouse was well-ventilated, the contribution to the total indoor radon concentration from the arsenic concentrate was less than 5 Bq m-3. This resulted in annual effective doses from radon exposure being below 20 μSv y-1. The results indicate that workers were not excessively exposed to radon (drastically below 100 Bq m-3) in the arsenic concentrate warehouse, despite the elevated 226Ra concentration, due to the good ventilation rate of the warehouse.