The thesis deals with the activities of the IRS units on-site of an emergency event, i.e. with focus on the crime scene investigation. The basic activities of the IRS units are to intervene, i.e. to avert danger or to mitigate and eliminate the consequences of an emergency event (fire, crash, explosion). However, the follow-up activities, especially the on-site investigation of an emergency event, is very important part of the activities of the IRS units, also with the possibility of cooperation of the law enforcement authorities. The aim of the thesis is to generally and comprehensively describe the activities of the IRS units during the investigation of the crime scene of an emergency event, from all points of view.