Braking system redundancy requirements for moving walks

• Redundancy of braking system of moving walks is required.
• A method of determination of SIL requirements is introduced.
• SIL-based reliability prognosis announces possible failures in advance.

The reliability of the braking system of moving walks plays a major role in the safe exploitation of these people movers. According to the requirements of the new standard ISO 22201-2, the reliability of a braking system of a moving walk has to correspond to safety integrity levels SIL1 till SIL3. In order to determine the required safety integrity level, a reliability analysis of a braking system has been performed using a probabilistic method and the Weibull distribution model. This paper presents the results of this reliability analysis and shows the necessity of redundancy of the braking system of public service moving walks. The results for the proposed redundant design show a higher reliability level and less reliability degradation in time than compared to braking system designs without redundancy. Based on these results and using a probabilistic and diagnostics approach, a suggestion for an intelligent system for preventing failure in a braking system is presented in this paper. This system maintains a required safety level of the braking system of a moving walk and predicts possible failures of the braking system.