The paper presents the results of the data analysis conducted at Bereznyaki Mine-2 of Uralkali in summer and winter (during the air pre-treatment period). The findings show that when mine air heaters are operating thermal drop of ventilation pressure appears in air supply shafts. It causes "airlocks" in the shafts -a phenomenon that nearly stops the airflow in one of the shafts while increasing dramatically the airflow in the other (others) air intake shafts. As a result, mine air heaters in the shafts may stop running which provokes freezing of the mine shaft shoring.The analysis of mine ventilation modes performed in summer and winter determined the factors affecting the occurrence of "airlocks" in the air supply shafts during air pre-treatment.