Abstract
The installation of various equipments and devices in close proximity necessitate the establishment of a design method capable of securing safety in a systematic manner. Regarding the safety index worked out for the sake of safety evaluation, including the reliability of safety devices, and the attention of operators/maintenance personnel, it is necessary to prepare the TAS (Tree Analysis for Safety) at each FA system, and though it is suitable to a system safety evaluation, it is inappropriate as a system safety functional design. In this paper, I show that the degree of surplus indicating the degree of accomplishment of the safety standard at each logical product can be defined. Using this degree of surplus, I propose the method seeking a combination of safety devices which can cope with the multiplexing of safety devices. Thus, I show that the safety functional design for FA systems can be constructed using the safety index
