This International Standard specifies the symbol to be used to signify the actual or potential presence of ionizing radiation and to identify objects, devices, materials or combinations of materials which emit ionizing radiation. For the purposes of this International Standard, ionizing radiation includes gamma and X-rays, alpha and beta particles, high-speed electrons, neutrons, protons and other nuclear particles; but not sound or radio waves, or visible, infra-red, or ultra-violet light. This International Standard does not specify the radiation levels at which the symbol is to be used.