AS/NZS IEC 60300.1:2015 pdf download – Dependability management Part 1: Guidance for management and application
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.
4.2 Benefits of dependability management Managing dependability results in benefits such as • meeting stakeholder requirements and objectives, • achieving expected service levels, • maintaining production or manufacturing capacity through increased availability, • improving safety when potential detrimental consequences are identified and dealt with appropriately, • reducing environmental impact when detrimental consequences are identified and dealt with appropriately, • increasing life and durability and reducing life cycle costs, and • improving quality. 4.3 Challenges of managing dependability 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. 5 System for managing dependability 5.1 Overview The purpose of a system for managing dependability is to direct and control an organization with regard to dependability, coordinating with other disciplines to provide an efficient and integrated effort to achieve objectives. Organizational policies and objectives may include dependability policies and objectives, which then lead to a dependability management system that can effectively implement them. Figure 2 shows dependability management as a part of a generic management system. The dependability management system results in a dependability programme which feeds into organizational plans and activities.