Abstract
Living assistance equipments are strongly needed not only a machine centered safety but also the concepts of human centered safety. A various structural & functional criteria should be based on the knowledge of anatomical & physiological characteristics. A risk has commonly given by relative and comparative expressions, whose styles are various survival or death ratio. The choice of risk are judged from the weight -ratio of benefit and disbenefit for group members or each person, and the death ratio for the risk is almost reduced to below 10^<-5>〜10^<-6>, and final judgments of accept or rejects for the criteria (level acceptable) depend on consciousness of social members. The ISS3 of TRISS mentions that the injured persons, being in death ratio 0.0035, are estimated as lifelong death ratio 5.8%, an average duration of life 2.7 years and an annual death rate 0.0007, if our life span is about 90 years and an operating time of those equipments reaches 4 hours every day. Those values are much smaller than ratio of automobiles or that of accidental death, and are same levels of the death rate of natural calamity. The TRISS has some defects: one of them is no considered effects of multiple traumas in our same region of our body, and the others are taking no accounts of an effect of aging for seniors. However, an estimation of TRISS becomes similar to that of ASCOT in the case of slight or severe injury, and accompanied with single trauma in the same region.
