On November 16, 2019, Laguna Verde NPP Unit 1 was increasing power from 65% after performing maintenance activities on one turbine stop valve. At 17:15 hrs. the physical security guard informed that the door to access the room TB-313 was closed but not correctly secured by its padlock. The room TB-313 is an area with radiation greater than 1000 mR/h. The event duration was 1:35 hrs. According to the investigation performed by radiation protection personnel, nobody accessed the room TB-313 while the condition lasted.