The invention pertains to a method and to an arrangement applicable to a container or to a chamber, for instance to a security chamber for valuable articles. The container/chamber(20) has a casing or shell (10) in which an explosive substance or a burstable item is housed. The arrangement has a detector (50, 50′) at the shell (10) for detecting ambient temperature or shell temperature. The explosive substance is detonated or the burstable item is depressurised to prevent bursting of the outer casing/shell (10)of the container or the chamber at a predetermined temperature limit value. The detector (50, 50′) for detecting the ambient temperature or the shell temperature is disposed essentially across the whole surface of the shell/casing (10).