AS NZS IEC 60300.1:2015 pdf download.Dependability management Part 1: Guidance for management and application.
4 Dependability management
4.1 Understanding dependability
Dependability is the ability of an item to perform as and when required. Dependability is thus the ability to fulfil the requirements and expectations of an item consistently over time. Dependability creates value in that the item retains its performance characteristics, operates as desired, and satisfies customer needs and expectations.
Management of dependability is a key element of an organization’s wider management systems in particular those for assets, finance and quality. Dependability management encompasses the planning and application of organizational arrangements, processes and associated methods and techniques to achieve the organization’s performance and product objectives.
Dependability is improved by systematically reducing the frequency of outages, product failures, service downtimes, and other undesired events and minimizing their effects. This is achieved by actions such as improving design, eliminating root causes of failure, simplifying complex processes, mitigating anomalies, promoting fault tolerance in design and fitness for use, advocating fault avoidance and error prevention, managing maintenance activities and making commitments to build trust and integrity to ensure user confidence throughout the life cycle. Early consideration of dependability in the life cycle is crucial since rectifying a design that causes poor dependability will often be more difficult, time consuming and costly at a later time.
Figure 1 illustrates the relationship of dependability to the needs of stakeholders and the requirements of an item. Depending on context， stakeholders can include users, owners, customers，government agencies， businesses and organizations responsible for ensuring dependability requirements are met.
Requirements are determined from the needs of stakeholders and from constraints such as the conditions of use, resources and legislation. They include functional requirements, which define what the item is required to do, and non-functional requirements, which specify additional attributes. Examples of functional requirements are capacity and power output and examples of non-functional requirements are safety, environmental sustainability and efficiency. Dependability requirements, which define the time-dependent ability to achieve dependability performance in these requirements consist of characteristics such as reliability, availability, maintainability and supportability.
Functional and non-functional requirements and dependability requirements are inter-related. A dependability requirement can only exist if there is a functional or non-functional requirement that has to be satisfied. There can be competing objectives between desirable requirements, such as safety or oil/gas production and dependability, and therefore trade-offs may be necessary. There can also be constraints related to cost, availability of item components or resources, or fixed timelines that could cause a compromise between functionality and dependability.
The perception of the ability to perform as and when required can vary for different stakeholders. Users, providers, operators, maintainers and others who interact with an item can have overlapping dependability requirements but with different application objectives and usage expectations. This can result in differing perceptions of dependability which might need to be considered while defining requirements.
Dependability includes objectively measureable characteristics, such as reliability, availability and maintainability, and more subjective judgements of trustworthiness relating to the functions required by particular stakeholders. The ability to measure the attainment of performance objectives is a fundamental consideration in setting the requirements.
Dependability includes both the ability to meet functional and non-functional requirements under normal and expected conditions, and the ability to adapt to unexpected changes in requirements, assumptions and circumstances to recover from external system failures.
Dependability needs to be addressed during the entire life cycle of an item. Early consideration and implementation of relevant dependability activities will better ensure that dependability requirements are achieved.
There can be complications when multiple organizations are involved, mid-life upgrading occurs, or the item’s dependability is influenced by interconnected and external systems.
Items are often integrated to operate with legacy items that are in different stages of the life cycle, with older generation technologies and methods of design. Dependability management needs to ensure interoperability and dependability of the integrated items through interface specifications to ensure dependable performance.
Systems are becoming more complex and can exhibit the characteristics of “open systems”, “systems of systems” or “unbounded or weakly bounded systems”. The systems can be managed by different parties that have different objectives and can be at different stages of the life cycle. This, together with the scale and complexity of the system makes it difficult for any stakeholder to comprehend the system as a whole and changes are thus less predictable and controllable. For that reason, it is crucial for stakeholders to understand and agree on the boundaries of their responsibilities and to assign accountability for implementation. Planning for dependability needs to take into account the potential for major failures and changes outside respective boundaries as well as inside.AS NZS IEC 60300.1 pdf download.