What is understood by Railway RAMS?
The concept of Railway RAMS is perfectly defined in CENELEC EN 50126 Standard, which develops specification and demonstration of reliability, availability, maintainability and safety (RAMS) of Railway Applications.
On the broader concept, Railway RAMS is described as a quantitative and qualitative indicator of the extent to which a system (or the components or sub-systems that form it) can be trusted to: (a) operating as specified, designed, manufactured and installed, (b) are available when they must operate and (c) are safe.
The purpose of a rail system is to achieve a rail traffic goal that we can express as a "Quality of Service". Two key points are included in this concept: safety and time (in reference to punctuality and periodicity). Therefore, the railway company RAMS describes the confidence with which a system can guarantee the achievement of such "Quality of Service" purpose.
The railway company RAMS is also intrinsically related to safety and availability. CENELEC standards interrelate them in the sense that a weak point in one or the other, or a poor management of conflicts arising between availability and safety requirements, can prevent a reliable system from being achieved.
Safety concepts are based on:
- Knowing the possible dangers in the system in its operating, maintenance and environment modes, with the severity of consequences produced by each hazard.
- System failure modes that could produce a hazard with probability of occurrence.
- Events, chain of events, environmental conditions, etc., in the application together with its probability of occurrence, which could cause an accident. Environment is undoubtedly a factor that will influence the functionality of the system and, in turn, safety.
- Maintainability of safety-related parts of the system -ease, probability of errors in maintenance actions and time to return the system to a safe state-.
- Influence of human factors both at operational and maintenance level.
It is important to be clear that ALL failures will adversely affect the reliability of a system, but only some failures will have an adverse effect on safety, under the scope of a specific application. Knowing this subset is imperative.
Availability concepts are based on:
- Reliability from the point of view of knowing all possible system failure modes, its associated probability of occurrence and its effect on system functionality.
- Maintainability (again), corrective and preventive.
- Possible impact of human factor on operation and maintenance with an impact on availability.