System safety development law and its application

The development law of System Safety Degree (SSD) is an important proposition of safety science which is important to guide safety management of enterprises and safety supervision of government. In this paper, the methods of theoretical and practical research are adopted. It is indicated that the relationship between SSD and safety investment is in direct ratio. The logistic model of the development law of SSD is set up under the condition of abundance safety input which obeys the law of safety retardarce increasing, otherwise, SSD follows the law of safety rehology-mutation, since the inverse Logistic model is set up under the condition of insufficient safety input. The evolution of SSD can be divided into 8 phases, i.e. increasing phase, accelerating increasing phase, slowness increasing phase, maximum safety degree keeping phase, slowness decreasing phase, accelerating attenuation phase, accident frequently happening phase and systemic destroying phase. It is illustrated by practical research that the Logistic model can be used to describe the development law of SSD. The model of safety rehology-mutation is applied in the forecasting of SSD and the decision-making of the safety investment of system.