Page 66 - 捷運技術 第43期

60 Andrea Colini 系統保證歐規與美規之介紹

1ePreface

For railway applications the RAMS Standards aim to promote a common understanding and

approach to the Management of Reliability, Availability, Maintainability, Safety. The systems-
level approach defined by these Standards facilitates assessment of the RAMS interactions between
elements of a complex distributed system such as a Metro line.

Combining contractual requirements and common practices, the main task for a good RAMS
Management Organization is to know how to use at the best each approach in order to build a Safe

and Reliable System.
Among the applicable standards there are several differences, mainly related on Safety
activities with a critical look into Hazard tracking and Risk Management issues. In particular, it is

widely recognized that the use of the CENELEC railway standards results in benefits concerning
safety and cross-acceptance for rail systems.
A formal approach to safety assessment and management allows to ensure the existence of a

fully documented, auditable safety management system, and identification and assessment of all
potential risks related to functional safety. The implication is that if a good safety management
system exists, and if risks are identified and controlled, an high level of safety will be assured.

Systematic identification and elimination of risks for a railway systems is obviously an important
aspect of design and development. To obtain this, high emphasis is laid by the applicable standards

on a suitable safety management supported by an appropriate safety organization.
This paper highlights the most relevant differences among U.S. and European approach
to RAMS and Safety. Starting from terminology, through the flow of technical safety activities

and the methodological approach to mishap risk management, there could be several benefits in
using European approach towards U.S. one. After a brief introduction to the MIL and CENELEC

guidelines for RAMS, the Hazard tracking and Risk resolution activities are pointed out in section
3. The formal approach of CENELEC on quantitative safety requirements (SIL concept) and safety
demonstration (Safety Cases) is described as strength of the European standard. Finally, in the

conclusion chapter, the main differences among the standards are summarized.

2eU.S. Military Standards

MIL-STD-882, “System Safety Program Requirements”, outlines a standard practice for
conducting system safety and provides a consistent means of evaluating identified risks.
According to this regulation, an SSPP (System Safety Program Plan), shall be prepared by
the supplier and developed for a specific product or application. This document defines the system

safety requirements to perform throughout the life cycle for any system, new development, upgrade,
modification, resolution of deficiencies, or technology development. Within the system life cycle,