The invention relates to a method and an arrangement (10) for detecting the penetration of optical radiation (12) in a sectional area (20) of a protective wall system (18) in which at least one receiver (22) is located. The receiver is connected to an evaluation circuit (24). To recognize the failure of an inner protective wall it is suggested that the outer wall (16) of the protective wall system has a breach (26) for a transmitter/receiver unit (28), consisting of a number of receivers (22) located on the circumferential side of a tubular jacket (30) and a number of transmitters (32) concentrically surrounding the receivers (22) in a circle.