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Machine safety is a prerequisite for accident-free working. A machine is considered to be safe if it does not pose any danger during regular use, and if even incorrect use or operation does not result in danger. The dangers referred to here may be mechanical, electrical or thermal, but also include noise, radiation or vibration. The basic safety requirements for dealing with these hazards are listed in the Machinery Directive 2006/42/EC. They are specified in more detail in harmonised European standards: the A, B and C standards.
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A-type standards are basic safety standards. They deal with basic concepts, design principles and general aspects that can be applied to machines. In terms of machine safety, EN ISO 12100 is the central A-type standard. It is listed under the Machinery Directive.
B-type standards are generic safety standards. They deal with a safety aspect (B1-type standards) or a type of safety feature (B2-type standards) that can be used for a whole range of machines.
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As a type-A standard, EN ISO 12100 contains general design principles for the design of safe machines. These are basic, pragmatic methods that can be applied to allow machines of all kinds to be designed safely in accordance with European legislation. EN ISO 12100 also specifies the risk assessment procedure in more detail. Such an assessment is necessary to reduce the risks posed to users by a machine to an acceptable level. The risk assessment consists of a risk analysis and a risk evaluation.
If the risk assessment shows that hazards exist, protective measures are required. Here too, DIN EN ISO 12100 provides guidance and describes how an existing risk can be reduced. A three-stage process is used: The first step concerns inherently safe designs. In the second step, technical and supplementary protective measures are described. Step 3 then identifies any user information that is required if there is still a risk, despite all the safety measures.
Additional precautions can further reduce the risk. These include, for example, controlled-stop devices that can be used to stop dangerous movement.
Due to increasing complexity, programmable control systems are being used more and more in machines and plants. Both EN ISO 13849 and IEC 62061 ensure their design complies with international legislation, e.g. the Machinery Directive.
In addition to the safety requirements, EN ISO 13849 also provides a guide for the principles of designing and integrating safety-related parts of control systems (SRP/CS) and software. These SRP/CS define properties that are required to perform the security function in question. For all SRP/CS – or any combination thereof – that map safety functions, the probability of failure must be estimated. This value is described using the Performance Level (PL).
IEC 62061 defines the requirements for safety-related electrical, electronic and programmable electronic control systems (SRECS). It also provides recommendations for their design, integration and validation. Non-electrical (for example, hydraulic or pneumatic) control elements are not covered by the standard. Safety integrity, as it is known, is expressed by a failure limit per IEC 62061. This limit refers to the probability of a dangerous failure occurring – for each safety function and per operating hour. This value is divided into four Safety Integrity Levels (SIL).
Regardless of which of the two standards is applied, they allow the machine manufacturer to assess when the relevant safety requirements are met. Which of the standards should be used in each specific case depends on the type of safety-related control systems involved.
A number of standards support engineers in selecting and designing special functions that can reduce the risk of the machine posing a hazard.
For example, ISO 14119 describes basic concepts and general design principles for interlocking devices and isolating safety features. This also includes requirements for the arrangement and fitting of position switches that can be used, for example, to monitor when a protective door is opened.
EN ISO 13850 defines the functional requirements for devices that immediately stop a machine in the event of an emergency (controlled stop devices). According to IEC 60204-1, controlled stop devices must be provided at all operator stations and other workplaces, unless a controlled stop device would not reduce the risk posed, or the machine is carried and guided by hand.
Frequently, accidents occur because a machine that was thought to have been shut down – for example for setup or troubleshooting – unexpectedly starts up again. EN 1037 defines safety design measures that can be used to prevent unexpected start-up. This includes, for example, devices for energy isolation and discharge.
Another safety device to reduce risk is two-hand control. This device prevents the operator of a machine from being able to reach into hazardous areas during dangerous operations. EN13851 (former EN 574) contains requirements and instructions for designing and selecting a device of this nature. The machines on which this safety device must be used are defined in the applicable C-type standards or the risk assessment results.
The central standard pertaining to machines’ electrical equipment is IEC 60204. The European version was updated in 2019 and has been mandatory for machine, plant and control panel manufacturers since mid-September 2021. Part 1 of the standard (IEC 60204-1) contains general requirements and defines general specifications and recommendations for the safety, functionality and maintenance of the electrical equipment of machines.
Numerous standards support engineers in designing a safe machine. These standards range from general recommendations for the design procedure to detailed requirements for safety devices. Following the various standards ensures that a machine will perform its functions without the risk of injury or damage to health.
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