The purpose of this paper is to set out the results of IRSN’s assessment of the safety distances to be implemented as first response to a transport accident involving radioactive material. It details the public health criteria and criteria used for selecting the accident situations covered. It then presents the safety distances calculated for each of the adopted scenarios. As the aim of this work is to help the emergency response teams set safety perimeters, three so-called reflex distances of 100 m, 500 m and 1000 m appropriate to the accident circumstances have been identified from the calculated distances. These distances may change while the accident is being dealt with as and when more precise information becomes available.