ac motor
160 7 chapter Personnal and machines safety Reminder of European legislation regarding safety for people and environment. Reminder of IEC regulation for machines and products. Examples of application, products and safety networks Summary7. Personnal and machines safety 161 1 2 3 4 5 6 7 8 9 10 11 12 M 7.1 Introduction 162 7.2 Industrial accidents 163 7.3 European legislation 165 7.4 Concept of safe operation 172 7.5 Certification and EC marking 173 7.6 Safety principles 175 7.7 Safety functions 176 7.8 Network safety 178 7.9 Example of application 179 7.10 Safety-related functions and products 181 7.11 Conclusion 182 7.1 Introduction 7. Personnal and machines safety 162 After presenting and defining the rules which govern safety, we shall focus on the machinery and the product technologies to meet customer requirements and comply with constr aints. 7.1 Introduction b Safety scope and definition Legislation requires us to take preventive action to preserve and protect the quality of the environment and the human health. To achieve these objectives, ther e are European Directives which must be applied by plant operators and by manufacturers of equipment and machines. It also assigns the responsibility for possible injury. • Notwithstanding the constraints, machine safety increases productivity by: - preventing industrial accidents, - ensuring the health and safety of all personnel by suitable safety measures that take into account the machine’s application and the local environment. • Cutting direct and indirect costs by: - reducing physical harm, - reducing insurance premiums, - reducing production loss and delay penalties, - limiting harm and cost of maintenance. • Safe operation involves two principles: safety and reliability of operation (C Fig.1) - Safety is the ability of a device to keep the risk incurred by persons within acceptable limits. - Reliability of operation is the ability of a system or device to perform its function at any moment in time and for a specified duration. • Safety must be taken into account fr om the design phase and kept in place thr oughout all stages of a machine’ s life cycle: transport, installation, adjustment, maintenance, dismantling. • Machines and plants are sources of potential risk and the Machinery Directive requires a risk assessment for every machine to ensure that any risk is less than the tolerable one. • Risk is defined in accordance with EN 1050 as follows (C Fig. 2): seriousness multiplied by the pr obability of occurrence. A Fig. 1 Safety and reliability of a system A Fig . 2 Definition of risk Risk related to potential hazar d =x Severity Of the possible harm for the consider ed hazard Pr obability of occurr ence Of the harm - frequency and duration of exposure - possibility of avoiding or limiting the harm - Pr obability of the occurr ence of an event which may cause harm 7.1 Introduction 7.2 Industrial accidents 7. Personnal and machines safety 163 • The European Standard EN1050 (Principles of Risk assessment) defines an iterative pr ocess to achieve safety in machinery. It states that the risk for each individual hazar d can be determined in four stages. This method provides the basis for the requisite risk reduction using the categories described in EN954. The diagram (C Fig. 3) shows this iterative process which will be detailed further on. 7.2 Industrial accidents An industrial accident occurs through work or in the workplace and causes minor to serious injury to a person operating or working on a machine (fitter , operator , maintenance worker , etc.). b Causes of accidents in the workplace • Human-related factors (designers, users) - Poor grasp of machine design. - Over-familiarity with danger through habit and failure to take danger ous situations seriously . - Underestimation of hazards, causing people to ignore safety guards. - Relaxed attention to supervisory tasks (fatigue). - Failure to comply with procedures. - Increased stress (noise, work rates, etc.). - Uncertainty of employment which can lead to inadequate training. - Inadequate or bad maintenance, generating unsuspected hazards. 7 A Fig. 3 Machine safety process 7.2 Industrial accidents 7. Personnal and machines safety 164 • Machine-related factors - Inadequate guards. - Sophisticated type of control and supervisory systems. - Inherent machine hazards (reciprocal motion of a machine, sudden starting or stopping). - Machines not suited to the application or environment (sound alarms deadened by the noise of surr ounding machinery). • Plant-related factors - Movement of personnel (automated production line). - Machinery from different sources and using different technologies. - Flow of materials or products between machines. b The consequences - Varying degrees of physical danger to the user. - Stoppage of the machine involved. - Stoppage of similar machine installations for inspection, for example by the Health and Safety Inspectorate. - Alterations to make machines comply with regulations where necessary. - Change of personnel and training new personnel for the job. - Damage to the company brand image. b Conclusion Damages for physical injuries are equivalent to about 20 billion euros paid out each year in the European Union. Decisive action is required to reduce the number of accidents in the workplace. The first essentials are adequate company policies and efficient organisation. Reducing the number of industrial accidents and injuries depends on the safety of machines and equipment. b Types of hazards The potential hazards of a machine can be classified in three main groups, as illustrated (C Fig. 4). A Fig. 4 The main hazards in a machine 7.3 European legislation 7. Personnal and machines safety 165 7.3 European legislation The main purpose of Machinery Directive 98/37/EC is to compel manufacturers to guarantee a minimum safety level for machinery and equipment sold within the EU. T o allow free circulation of machinery within the European Union, the EC marking must be applied to the machine and an EC declaration of compliance issued to the purchaser. This directive came into effect in January 1995 and has been enforced since January 1997 for all machines requiring compliance. The user has obligations defined by the health and safety dir ectives 89/655/EEC which ar e based on all standards. b Standards v Introduction The harmonized European safety standards establish technical specifications which comply with the minimum safety requirements defined in the related directives. Compliance with all applicable harmonized Eur opean standards ensures compliance with the related directive. The main purpose is to guarantee a minimum safety level for machinery and equipment sold within the EU market and allow the free circulation of machinery within the European Union. v Three groups of European standards • A standards Basic safety standards which specify the basic concepts, design principles and general aspects valid for all types of machines. EN ISO 12100 (former EN292). • B standards Safety standards applying to specific aspects of safety or a particular device valid for a wide range of machines. • B1 standards Standards applying to specific safety aspects of electrical equipment of machines: EN 60204-1 (e.g.: Noise, safety distances, control systems, etc). • B2 standards Standards applying to emergency stop safety devices, including two- handed control stations (EN 574), safety guards (EN 418), etc. • C standards Safety standar ds stating detailed safety prescriptions applicable to a specific machine or group of machines (e.g.: EN 692 for hydraulic presses or robots). The figure 5 shows the non-exhaustive scope of the standards. 7 A Fig .5 Safety standards 7.3 European legislation 7. Personnal and machines safety 166 The figure 6 lists the main European safety standards. Standards Type Subject EN ISO 12100-1, -2 A Machinery safety - basic concepts, principles for design Part 1 Terminology Part 2 principles EN 574 B Two-handed control devices - design principles EN 418 B Emer gency stop equipment - design principles EN 954-1 B Safety-related parts of control systems - design principles EN 349 B Minimum gaps to avoid crushing of human body parts EN 294 B Safety distances to prevent danger zones being reached by the upper limbs EN 811 B Safety distances to prevent danger zones being reached by the lower limbs EN 1050 B Machinery safety - Principles for risk assessment EN 60204-1 B Machinery safety - Electrical equipment of machines Part 1: general requirements EN 999 B Positioning of protective equipment in respect of approach speeds of body parts EN 1088 B Locking devices associated with guards - design and selection principles EN 61496 B Electro-sensitive protective equipment Part 1 general requirement Part 2 particular requirement for light barrier EN 1037 B Prevention of unexpected start-up EN 60947-5-1 B Switching for LV electromechanical control circuits N 842 B Visual danger signals - General requirements, design and testing EN 201 C Safety requirements for injection moulding machines for plastics and rubber EN 692 C Safety requirements for mechanical presses EN 693 C Safety r equir ements for hydraulic presses EN 289 C Safety requirements for moulding machines by compr ession and by transfer EN 422 C Safety requirements for design and construction of moulding machines by metal blowing EN 775 C Manipulating industrial robots - safety requirements EN 415-4 C Packaging machines Part 4: palletisers - safety requirements EN 619 C Safety and EMC requirements for equipment for mechanical handling of unit loads EN 620 C Safety and EMC r equir ements for fixed belt conveyors for bulk material EN 746-3 C Industrial thermo pr ocessing equipment Part 2: Safety r equir ements for the generation and use of atmosphere gases EN 1454 C Safety r equir ements for portable disc cutting machines with thermal motor A Fig . 6 Some machiner y safety r equirements 7.3 European legislation 7. Personnal and machines safety 167 v EN 954-1 Safety related parts of Control systems Standard EN 954-1 “Safety related parts of control systems” came into for ce in March 1997. This type B standard stipulates the safety-related requirements for control systems. It specifies their categories and describes the characteristics of their safety functions. In type C standar ds, these parts of the system are called categories. In this standard, performance of safety-related parts with regard to occurrence of faults is classified in five categories. (B, 1, 2, 3, 4). An upgrade (prEN ISO 13849-1) is in the planning stage. • Fault categories (C Fig.7) 7 A Fig.7 The five fault categories A Fig. 8 Choice table System behaviour Principles to achieve safety B A fault can lead to loss of the safety Component selection function. 1 As for category B but higher reliability Component selection r equired of the safety function. 2 A fault can lead to loss of the safety Self-monitoring function between inspection periods. Loss of the safety function is detected by the control (at each test). 3 For a single fault, the safety function is Redundancy always ensured. Only a few faults will be detected. Accumulation of undetected faults can lead to loss of the safety function. 4 When faults arise, the safety function is Redundancy + self-monitoring always ensured. Faults will be detected in time to prevent loss of the safety function(s). + • Risk graph According to the definition of risk, standard EN 954-1 defines a practical method for selecting a category of contr ol system and covers: - S : Seriousness of injury. - F : Fr equency and/or exposur e to a hazar d. - P : Possibility of preventing accident. Resulting categories define resistance to faults and the behaviour of control systems in the event of a fault (C Fig. 8). S Accident result S1 Slight injury S2 Serious or permanent injury to or death of a person F Pr esence in the danger zone F1 Rar e to fairly fr equent F2 Frequent to permanent P Possibility of preventing accident P1 Possible in certain circumstances P2 Virtually impossible 7.3 European legislation 7. Personnal and machines safety 168 To illustrate those concepts we present an assessment of risk in a hydraulic press with manual materiel feeding (C Fig. 9). - Seriousness of injury: S2 since serious permanent injury could occur. - Frequency and exposure time: F2 since the operator is permanently present. - Possibility of avoiding the hazard: P2since it is virtually impossible to avoid. The result on the risk graph is category 4. To supplement this example we will select the guard locking devices (EN 1088 standard). In this example (C Fig. 10) the diagram conforms to category 4. When faults occur, they are detected in time to prevent loss of the safety function. v Functional safety and safety integrity level (SIL) New technologies help to make savings which can be achieved by implementing an intelligent safety strategy. This standard takes into account the use of these new technologies in safety products and solutions and provides guidelines to calculate the probability of failures. More and more devices and products dedicated to machinery safety now incorporate complex programmable electronic systems. The complexity of these systems makes it difficult in practice to determine the behaviour of such safety devices in the event of a fault. This is why standard IEC/EN 61508 entitled “Functional safety of electrical, electronic and programmable electronic systems” provides a new approach by considering the reliability of safety functions. It is a basic safety standard for industry and the process sectors. IEC/EN 62061 stipulates the requirements and makes recommendations for the design, integration and validation of safety-related electrical, electronic and programmable electronic control systems (SRECS) for machinery within the framework of IEC/EN 61508. EN 62061 is harmonised with the European Machinery Directive. The Safety Integrity Level (SIL) is the new measur e defined in IEC 61508 regarding the probability of failure in a safety function or system. A Fig. 9 Assessment of risk in a hydraulic press A Fig. 10 Guard locking application 7.3 European legislation 7. Personnal and machines safety 169 • Definition of Functional Safety according to IEC/EN 61508 Functional safety is a part of the overall safety of equipment under contr ol (EUC). It depends on the correct functioning of safety-related systems which include electrical, electronic and programmable electronic parts and other exter nal risk reduction devices. • Safety Integrity Level (SIL) There are two ways to define the SIL, depending on whether the safety system is run in low demand mode or in continuous or high demand mode (C Fig . 11) . The scale of functional safety is on 4 levels, fr om SIL1 to SIL4, the latter having the highest level of safety integrity. Safety is achieved by risk reduction (IEC/EN 61508) (C Fig.12). The residual risk is the risk remaining after protective measures have been taken, Electrical, Electronic and Programmable Electronic safety-related systems (E/E/EP) contribute to risk reduction. Safety integrity levels estimate the pr obability of failur e. For machinery , the probability of dangerous failure per hour in a control system is denoted in IEC/EN 62061 as the PFHd (C Fig.13). 7 A Fig. 12 Position of standard EN 61508 and related standards A Fig. 11 Risk reduction [...]... process 7 Personnal and machines safety 7. 6 7. 6 Safety principles Safety principles b Guidelines for building a safety control Standard EN 954-1 defines the safety requirements for safety related parts of a control system It defines 5 categories and describes the specific properties of their safety functions, which are: - basic safety principles, - tried and tested safety principles, - tried and tested components... part of the work zone Category 4 XPS MC Software-configured function Protection of fingers and hands in danger zone category 4 XPS MF Protection of operator accessing a danger zone Safety- related PLC Programmable software Category 4 Protection of operator accessing a series of danger zones category 4 181 7 Personnal and machines safety 7. 10 7. 11 Safety- related functions and products Conclusion b ASI Safety. .. the theoretical test 172 7 Personnal and machines safety 7. 5 7. 5 Certification and EC marking Certification and EC marking There are 6 steps in the process of machinery certification and EC marking: 1 application of all relevant directives and standards, 2 compliance with essential health and safety requirements, 3 technical documentation, 4 compliance inspection, 5 declaration of compliance, 6 EC marking... circuit, the safety diagram is much more complex This is why it is advisable to use a safety module The diagram (C Fig.26) represents an emergency stop function for 2 circuits A Fig 26 Emergency stop for 2 circuits 177 7 Personnal and machines safety 7. 7 7. 8 Safety functions Network safety The diagram (C Fig. 27) shows how an emergency stop is linked to a speed controller (stop category 1) A Fig 27 7.8 Emergency... Mechanically linked contacts 175 7 7 Personnal and machines safety 7. 6 7. 7 Safety principles Safety functions Definition of mechanically linked contacts (IEC/ EN 609 47- 5-1): “[…] a combination of n N/C contact element(s) and b N/O contact element(s) designed so that they cannot be closed simultaneously When an N/C contact is maintained in the closed position a minimum gap of 0.5mm between all N/O contacts... figure 16 shows the process of risk assessment for a machine A Fig 16 Assessment process 171 7 7 Personnal and machines safety 7. 4 7. 4 Concept of safe operation Concept of safe operation Safe operation is the practice of the principles described above and is a global concept which covers several aspects: - machine design and production integrating risk assessment, - installation and implementation with... 13 -7 -6 SIL integrity level -6 -5 IEC 61508 considers two modes of operation: - high demand or continuous mode – where the frequency of demand made on a safety- related system is greater than one per year or greater than twice the proof test frequency, - low demand mode – where the frequency of demand made on a safety- related system is no greater than one per year and no greater than twice the proof... the compliance of the product 173 7 7 Personnal and machines safety 7. 5 Certification and EC marking b Conformity assessment According to article 8 of the Machinery Directive the manufacturer (or his authorised representative established in the Community) must draw up an EC declaration of conformity for all machinery (or safety components) This must be done to certify that machinery and safety components... 29 Two-handed control with ASI bus The time lapse between the actions on the two controls must not exceed 0.5 seconds and the controls must be in operation throughout the entire length of the hazardous machine process 7 7.9 Example of application The application described and illustrated (C Fig.30) is a practical example of some safety functions A Fig 30 Example of application 179 7 Personnal and machines... applications: - small and medium automatic machines, - packaging machines, textile machines, conveyor belts, water distribution, wastewater treatment, etc, - automated standalone subsystems relating to medium to large machines 180 7 Personnal and machines safety 7. 10 7. 10 Safety- related functions and products Safety- related functions and products b Schneider Electric has a wide range of safety- related products . principles 175 7. 7 Safety functions 176 7. 8 Network safety 178 7. 9 Example of application 179 7. 10 Safety- related functions and products 181 7. 11 Conclusion. Introduction 162 7. 2 Industrial accidents 163 7. 3 European legislation 165 7. 4 Concept of safe operation 172 7. 5 Certification and EC marking 173 7. 6 Safety principles