Introduction The structure of safety standards in the field of machinery is as follows.
a) Type-A standards (basis standards) give basic concepts, principles for design and general aspects that can be applied to machinery.
b) Type-B standards (generic safety standards) deal with one or more safety aspect(s), or one or more type(s) of safeguards that can be used across a wide range of machinery:
- type-B1 standards on particular safety aspects (e.g. safety distances, surface temperature, noise);
- type-B2 standards on safeguards (e.g. two-hands controls, interlocking devices, pressure sensitive devices, guards).
c) Type-C standards (machinery safety standards) deal with detailed safety requirements for a
particular machine or group of machines.
This part of ISO 13849 is a type-B-1 standard as stated in ISO 12100.
This document is of relevance, in particular, for the following stakeholder groups representing the market players with regard to machinery safety:
- machine manufacturers (small, medium and large enterprises);
- health and safety bodies (regulators, accident prevention organisations, market surveillance etc.).
Others can be affected by the level of machinery safety achieved with the means of the document by the above-mentioned stakeholder groups:
- machine users/employers (small, medium and large enterprises);
- machine users/employees (e.g. trade unions, organizations for people with special needs);
- service providers, e. g. for maintenance (small, medium and large enterprises);
- consumers (in case of machinery intended for use by consumers).
The above-mentioned stakeholder groups have been given the possibility to participate at the drafting
process of this document.
In addition, this document is intended for standardization bodies elaborating type-C standards. The requirements of this document can be supplemented or modified by a type-C standard.
For machines which are covered by the scope of a type-C standard and which have been designed and built according to the requirements of that standard, the requirements of that type-C standard take precedence.
When provisions of a type-C standard are different from those which are stated in type-A or type-B standards, the provisions of the type-C standard take precedence over the provisions of the other standards for machines that have been designed and built according to the provisions of the type-C standard.
This part of ISO 13849 is intended to give guidance to those involved in the design and assessment of control systems, and to Technical Committees preparing type-B2 or type-C standards which are presumed to comply with the Essential Safety Requirements of Annex I of the Directive 2006/42/EC on machinery. It does not give specific guidance for compliance with other EC directives.
As part of the overall risk reduction strategy at a machine, a designer will often choose to achieve some measure of risk reduction through the application of safeguards employing one or more safety functions.
Parts of machinery control systems that are assigned to provide safety functions are called safety- related parts of control systems (SRP/CS) and these can consist of hardware and software and can either be separate from the machine control system or an integral part of it. In addition to providing safety functions, SRP/CS can also provide operational functions (e.g. two-handed controls as a means of process initiation).
The ability of safety-related parts of control systems to perform a safety function under foreseeable conditions is allocated one of five levels, called performance levels (PL). These performance levels are defined in terms of probability of dangerous failure per hour (see Table 2).
The probability of dangerous failure of the safety function depends on several factors, including hardware and software structure, the extent of fault detection mechanisms [diagnostic coverage (DC)], reliability of components [mean time to dangerous failure (MTTFD), common cause failure (CCF)], design process, operating stress, environmental conditions and operation procedures.
In order to assist the designer and facilitate the assessment of achieved PL, this document employs a methodology based on the categorization of structures according to specific design criteria and specified behaviours under fault conditions. These categories are allocated one of five levels, termed Categories B, 1, 2, 3 and 4.
The performance levels and categories can be applied to safety-related parts of control systems, such as
- protective devices (e.g. two-hand control devices, interlocking devices), electro-sensitive protective devices (e.g. photoelectric barriers), pressure sensitive devices,
- control units (e.g. a logic unit for control functions, data processing, monitoring, etc.), and
- power control elements (e.g. relays, valves, etc.),
as well as to control systems carrying out safety functions at all kinds of machinery — from simple (e.g. small kitchen machines, or automatic doors and gates) to manufacturing installations (e.g. packaging machines, printing machines, presses).
This part of ISO 13849 is intended to provide a clear basis upon which the design and performance of any application of the SRP/CS (and the machine) can be assessed, for example, by a third party, in-house or by an independent test house.
Information on the recommended application of IEC 62061 and this part of ISO 13849
IEC 62061 and this part of ISO 13849 specify requirements for the design and implementation of safety- related control systems of machinery. The use of either of these International Standards, in accordance with their scopes, can be presumed to fulfil the relevant essential safety requirements. ISO/TR 23849 gives guidance on the application of this part of ISO 13849 and IEC 62061 in the design of safety-related control systems for machinery.
As with ISO/TR 23849, ISO/TR 22100-2 has been added to the list of normative references given in Clause 2 — the latter owing to its importance for an understanding of the relationship between this part of ISO 13849 and ISO 12100. |