1、BRITISH STANDARD BS 4778-3.1: 1991 Quality vocabulary Part 3: Availability, reliability and maintainability terms Section 3.1 Guide to concepts and related definitionsBS4778-3.1:1991 This British Standard, having been prepared under the directionof the Quality, Management and Statistics Standards Po
2、licy Committee, waspublished under the authorityof the Standards Boardand comes into effect on 31 October 1991 BSI 12-1998 First published as part of BS 4778-2:1979 Second edition October 1991 The following BSI references relate to the work on this standard: Committee reference QMS/23 Draft for comm
3、ent 90/97333 DC ISBN 0 580 19753 0 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Quality, Management and Statistics Standards Policy Committee (QMS/-) to Technical Committee QMS/23, upon which the following bodies were represented: Ass
4、ociation for Consumer Research (ACRE) Association of Consulting Engineers British Gas plc British Railways Board British Telecommunications plc Cable and Wireless plc Civil Aviation Authority Cranfield Information Technology Institute Cranfield Institute of Technology EEA (the Association of Electro
5、nics, Telecommunications and Business Equipment Industries) Electricity Supply Industry in United Kingdom Electronic Components Industry Federation Engineering Equipment and Materials Users Association GAMBICA (BEAMA Ltd.) Institute of Quality Assurance Institution of Electrical Engineers Institutio
6、n of Plant Engineers Ministry of Defence National Computing Centre Ltd. Railway Industry Association of Great Britain Society of British Aerospace Companies Limited United Kingdom Atomic Energy Authority Amendments issued since publication Amd. No. Date CommentsBS4778-3.1:1991 BSI 12-1998 i Contents
7、 Page Committees responsible Inside front cover Foreword ii Section 1. General 1 Scope 1 2 Arrangement 1 3 Terms which merit special note 1 4 References 1 Section 2. Hazard, risk and safety 5 Relationship of terms 2 6 Hazard 2 7 Risk 2 8 Risk management 2 9 Economic risk 3 10 Hazard and risk to the
8、environment 3 11 Safety 3 Section 3. Availability 12 Availability 4 Section 4. Reliability 13 Reliability 5 14 Reliability characteristics 5 Section 5. Maintainability 15 Maintainability 8 Section 6. Maintenance 16 Maintenance 9 17 Time analyses of maintenance 9 Section 7. ARM data and characteristi
9、cs 18 ARM data 12 19 ARM characteristics 12 Section 8. ARM improvement 20 ARM management and assurance processes and programmes 14 Section 9. Human aspects of reliability 21 Human reliability 15 Section 10. Reliability and software 22 Programmable system software 16 Appendix A English words and comm
10、only used terms 17 Index 18 Figure 1 Example of the variation of failure rate with time 7 Figure 2 Forms of maintenance 10 Figure 3 Maintenance times 11 Figure 4 General relationship of ARM characteristic terms 13 Publication(s) referred to Inside back coverBS4778-3.1:1991 ii BSI 12-1998 Foreword Th
11、is Part of BS4778 has been prepared under the direction of the Quality, Management and Statistics Standards Policy Committee. Together with BS4778-2:1991 it revises and extends the terms defined in BS4778-2:1979 and contains terms and definitions for availability, reliability and maintainability. Th
12、is Part of BS4778 is issued in two Sections as follows. This Section contains definitions of terms not included in Section 3.2 which the UK considers important in this field of application, and also the concepts of many of the terms contained in Section 3.2 to which direct reference is made. Section
13、 3.2 is identical with IEC50(191), International electrotechnical vocabulary, Chapter191, Dependability and quality of service, published by the International Electrotechnical Commission (IEC). Section 3.2 contains an extensive vocabulary of availability, reliability and maintainability terms in the
14、 preparation of which the UK has taken an active role. NOTEIt has been decided to reproduce as a dual-numbered British Standard, the four language revisions of the definitions and the seven language translations of the terms. BS4778 will be published in three Parts as follows. Part 1: International
15、terms; Part 2: Guide to quality concepts and related definitions; Part 3: Availability, reliability and maintainability terms. Previous editions of BS4778 were arranged in a conceptual format which provided additional explanation and perspective for the major terms defined, as well as the formal def
16、initions themselves. Many users found this conceptual approach helpful and this has been retained in BS4778-2 and in Section3.1. BS4778-1 and Section3.2 do not include concepts. The relationship between BS4778-3, some other British Standard glossaries, IEC50(191) and ISO8402 is listed. International
17、 standard British Standard BS 4778 Quality vocabulary ISO8402 Quality vocabulary Part 1:1987 International terms (Identical) Not applicable Part 2:1991 Quality concepts and related definitions Not applicable Part 3: Availability, reliability and maintainability terms Section 3.1:1991 Guide to concep
18、ts and related definitions IEC Publication 50: International electrotechnical vocabulary Chapter 191 Dependability and quality of service Section 3.2:1991 Glossary of international terms (Identical) BS4727 1)Glossary of electrotechnical, power, telecommunications, electronic lighting and colour term
19、s Other Chapters of IEC50 Parts 1 to 5 (Mostly technically equivalent) 1) Published under the direction of the Electrotechnical Standards Policy Committee.BS4778-3.1:1991 BSI 12-1998 iii Attention is drawn to definitions of terms used in closely related fields given in BS2846, BS3811, BS4727 and BS5
20、532. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document compr
21、ises a front cover, an inside front cover, pages i to iv, pages1to 22, aninside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on theinside front cover.iv blankBS4778-3.1:1991 BS
22、I 12-1998 1 Section 1. General 1 Scope This Part of BS4778 gives guidance on concepts and defines terms used in the disciplines of availability, reliability and maintainability (ARM). Its object is to assist understanding and communication in these fields. NOTE 1The acronym ARM is used in this docum
23、ent to avoid making the text cumbersome; its use has no other significance and other acronyms such as RAM or R and M could equally serve the purpose. NOTE 2The titles of publications referred to in this standard are listed on the inside back cover. 2 Arrangement This Part of BS4778 is subdivided int
24、o the following two Sections. a) This Section explains concepts underlying several major subject areas and also provides definitions of some additional national terms not included among the internationally accepted terms in Section 3.2. It also includes supplementary vocabularies for some topics, e.
25、g.human reliability, not covered by Section 3.2. b) Section 3.2 contains the internationally agreed definitions of terms listed in IEC50(191). 3 Terms which merit special note 3.1 Defect Care should be taken in the use of this term. In the United Kingdom the term is frequently used for a product or
26、service that is found to be unfit for its intended usage. Some national and international glossaries relate defect to a condition that renders an item unsafe or incapable of meeting functional or other customer expectation. The IEC concept of a defect relates to all conditions that can give rise to
27、losses and product liability. Legislation varies widely from one authority to another. It appears likely that the definition of defect will remain under review for some considerable time and caution should be exercised in the use of this term. The term should not be used as a general term and it wou
28、ld be prudent to avoid its use altogether if possible. 3.2 Item Differing definitions of and associated notes on the term “item” appear in BS4778-3.2 and BS5532-1. This is mainly due to translation problems at the international level, but it is hoped that the differences can be resolved in future ed
29、itions. The notes accompanying the definition of item in 191-01-01 of BS4778-3.2:1991 explain this problem succinctly and allow the French version to use the term “entit” while the English version uses the term “item”. This concept is extended to derived compound terms. 4 References AppendixA lists
30、ordinary English words adopted as “terms” in quality and reliability activities with their everyday meaning.BS4778-3.1:1991 2 BSI 12-1998 Section 2 Section 2. Hazard, risk and safety 5 Relationship of terms The purpose of this section is to provide an understanding of the relation between hazard, ri
31、sk and safety and ARM terms. 6 Hazard 6.1 Concept A general concept of a hazard as applied, for example, to an industrial process, or a commercial organization, is the potential for adverse consequences of some primary event, sequence of events or combination of circumstances. Hazards can be classif
32、ied according to the severity of their potential effects, either in terms of safety, economics or other consequences. Different industries use different classifications. Such classifications alone are purely subjective and usually require qualification and quantification, by definition of the precis
33、e form of the hazard and a quantified evaluation of the consequences. 6.2 Terms 6.2.1 hazard A situation that could occur during the lifetime of a product, system or plant that has the potential for human injury, damage to property, damage to the environment, or economic loss. 6.2.2 major hazard A l
34、arge scale hazard which may have severe consequences. 6.2.3 hazard analysis The identification of hazards and the consequences of the credible accident sequences of each hazard. 7 Risk 7.1 Concept A general concept of risk is the chance, in quantitative terms, of a defined hazard occurring. It there
35、fore combines a probabilistic measure of the occurrence of the primary event(s) with a measure of the consequences of that/those event(s). Criteria for acceptability of some predicted risk or measured risk can be set voluntarily by the organization responsible and/or subjected to the hazard, or be s
36、et mandatorily by some regulatory organization. 7.2 Terms 7.2.1 risk A combination of the probability, or frequency, of occurrence of a defined hazard and the magnitude of the consequences of the occurrence. 7.2.2 risk criteria A qualitative and quantitative statement of the acceptable standard of r
37、isk with which the assessed risk needs to be compared. 7.2.3 risk assessment The integrated analysis of the risks inherent in a product, system or plant and their significance in an appropriate context. 7.2.4 risk quantification The estimation of a given risk by a statistical and/or analytical model
38、ling process. NOTEThis may be done by such logic tree modelling methods as are employed in hazard analysis, or by statistical inferences from historical accident data derived from past circumstances similar to those of the product or system or planned operation of facilities, i.e. by developing prob
39、abilities of future accidents from files of historical reports of such accidents. 7.2.5 risk evaluation The appraisal of the significance of a given quantitative (or, when acceptable, qualitative) measure of risk. 7.2.6 individual risk The frequency at which an individual may be expected to sustain
40、a given level of harm from the realization of specified hazards. 7.2.7 societal risk The relationship between frequency of occurrence and the number of people in a given population suffering from a specified level of harm from the realization of specified hazards. 8 Risk management 8.1 Concept The o
41、verall subject area concerned with hazard identification, risk analysis, risk criteria and risk acceptability, is generally known as risk management (see8.2.1) or loss prevention (see9.2.2). This includes the various techniques that have been developed for the assessment and control of risk. These t
42、echniques include the probabilistic assessment of reliability for the quantification of the chance of a hazard occurring. 8.2 Term 8.2.1 risk management The process whereby decisions are made to accept a known or assessed risk and/or the implementation of actions to reduce the consequences or probab
43、ility of occurrence.BS4778-3.1:1991 BSI 12-1998 3 Section 2 NOTEA compromise is made considering increased cost, schedule requirements and effectiveness of redesign or retraining, installation of warning and safety devices and procedural changes. Risk management is also concerned with the mitigation
44、 of those risks deriving from unavoidable hazards through the optimum specification of warning and safety devices and risk control procedures, such as contingency plans and emergency actions. 9 Economic risk 9.1 Concept Economic risks are related to financial losses that represent the commercial con
45、sequences of a hazard. These consequences can include the loss of capital investment in a process plant or other commercial venture, together with the loss of the product of that process or venture. For example, the risk could be the damage caused by a fire in a production plant and the loss of expe
46、cted future production in that plant. The loss can be either partial or total, temporary or permanent. 9.2 Terms 9.2.1 economic risk The risk of financial loss associated with a product, system or plant due to potential hazards causing loss of production, damage or other financial consequence. NOTER
47、isks to human safety can also have economic consequences. 9.2.2 loss prevention A systematic approach to preventing hazardous events or minimizing their effects. NOTEThe activities may be associated with financial loss or safety issues. They are a form of risk management, but are not necessarily qua
48、ntitative. 9.2.3 capital cost The total cost to the owner of acquiring an item and bringing it to the condition where it is capable of performing its intended function. 9.2.4 operating cost The total cost to the owner of the operation, maintenance and modification of a system or plant. 9.2.5 mainten
49、ance cost The total cost of retaining an item in, or restoring it to, a state in which it can perform its required function. 9.2.6 life-cycle cost The total cost of ownership of an item taking into account all the costs of acquisition, personnel training, operation, maintenance, modification and disposal. NOTEConsideration of life-cycle cost may be important in making decisions on new or changed requirements and as a control mechanism in service, for existing and future items. 10 Hazard and risk to the environment 10.1 Concept The concepts of hazard and risk c
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