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Moving Parts of Machines

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This article discusses situations and chains of events leading to accidents attributable to contact with the moving part of machines. People who operate and maintain machinery run the risk of being involved in serious accidents. US statistics suggest that 18,000 amputations and over 800 fatalities in the United States each year are assignable to such causes. According to the US National Institute for Occupational Safety and Health (NIOSH), the “caught in, under, or between” category of injuries in their classification ranked highest among the most important kinds of occupational injuries in 1979. Such injuries generally involved machines (Etherton and Myers 1990). “Contact with moving machine part” has been reported as the principal injury event in just over 10% of occupational accidents ever since this category was introduced into Swedish occupational-injury statistics in 1979.

Most machines have moving parts that can cause injury. Such moving parts may be found at the point of operation where work is performed on the material, such as where cutting, shaping, boring or deforming takes place. They may be found in the apparatus which transmits energy to the parts of the machine carrying out the work, such as flywheels, pulleys, connecting rods, couplers, cams, spindles, chains, cranks and gears. They may be found in other moving parts of the machine such as wheels on mobile equipment, gear motors, pumps, compressors and so forth. Hazardous machine movements can also be found among other sorts of machinery, especially in the auxiliary pieces of equipment which handle and transport such loads as work pieces, materials, waste or tools.

All parts of a machine that move in the course of the performance of work may contribute to accidents causing injury and damages. Both rotating and linear machine movements, as well as their sources of power, can be dangerous:

Rotating motion. Even smooth rotating shafts can grip an item of clothing and, for example, draw a person’s arm into a hazardous position. The danger in a rotating shaft increases if it has projecting parts or uneven or sharp surfaces, such as adjusting screws, bolts, slits, notches or cutting edges. Rotating machine parts give rise to “nip points” in three different ways:

  1. There are the points between two rotating parts that rotate in opposite directions and have parallel axes, such as gears or cog-wheels, carriage rollers or mangles.
  2. There are the points of contact between rotating parts and parts in linear movement, such as found between a power-transmission belt and its pulley, a chain and a sprocket, or a rack and pinion.
  3. Rotating machine movements can give rise to the risk of cuts and crushing injuries when they take place in close proximity to stationary objects—this sort of condition exists between a worm conveyor and its housing, between the spokes of a wheel and the machine bed, or between a grinding wheel and a tool jig.

 

Linear movements. Vertical, horizontal and reciprocating motion can cause injury in several ways: a person may receive a shove or blow from a machine part, and may be caught between the machine part and some other object, or may be cut by a sharp edge, or sustain a nip injury by being trapped between the moving part and another object (figure 1).

Figure 1. Examples of mechanical movements that can injure a person

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Power sources. Frequently, external sources of power are employed to run a machine which may involve considerable quantities of energy. These include electric, steam, hydraulic, pneumatic and mechanical power systems, all of which, if released or uncontrolled, can give rise to serious injuries or damage. A study of accidents that occurred over one year (1987 to 1988) among farmers in nine villages in northern India showed that fodder-cutting machines, all otherwise of the same design, are more dangerous when powered by a motor or tractor. The relative frequency of accidents involving more than a minor injury (per machine) was 5.1 per thousand for manual cutters and 8.6 per thousand for powered cutters (Mohan and Patel 1992).

Injuries Associated with Machine Movements

Since the forces associated with machine movements are often quite large, it can be presumed that the injuries to which they give rise will be serious. This presumption is confirmed by several sources. “Contact with moving machinery or material being machined” accounted for only 5% of all occupational accidents but for as much as 10% of fatal and major accidents (fractures, amputations and so on) according to British statistics (HSE 1989). Studies of two vehicle-manufacturing workplaces in Sweden point in the same direction. Accidents caused by machine movements gave rise to twice the number of days of sick leave, as measured by median values, compared to non-machine-related accidents. Machine-related accidents also differed from other accidents with regard to part of the body injured: The results indicated that 80% of the injuries sustained in “machine” accidents were to the hands and fingers, while the corresponding proportion for “other” accidents was 40% (Backström and Döös 1995).

The risk situation at automated installations has turned out to be both different (in terms of type of accident, sequence of events and degree of injury severity) and more complicated (both in technical terms and with regard to the need for specialized skills) than at installations where conventional machinery is used. The term automated is herein meant to refer to equipment which, without the direct intervention of a human being, can either initiate a machine movement or change its direction or function. Such equipment requires sensor devices (e.g., position sensors or microswitches) and/or some form of sequential controls (e.g., a computer program) to direct and monitor their activities. Over recent decades, a programmable logic controller (PLC) has been increasingly employed as the control unit in production systems. Small computers are now the most common means used for controlling production equipment in the industrialized world, while other means of control, such as electro-mechanical units, are becoming less and less common. In the Swedish manufacturing industry, the use of numerically controlled (NC) machines increased by 11 to 12% per year over the 1980s (Hörte and Lindberg 1989). In modern industrial production, being injured by “moving parts of machines” is increasingly becoming equivalent to being injured by “computer-controlled machine movements”.

Automated installations are found in more and more sectors of industry, and they have an increasing number of functions. Stores management, materials handling, processing, assembly and packaging are all being automated. Series production has come to resemble process production. If the feeding, machining and ejection of work pieces are mechanized, the operator no longer needs to be in the risk zone during the course of regular, undisturbed production. Research studies of automated manufacturing have shown that accidents occur primarily in the handling of disturbances affecting production. However, people can also get in the way of machine movements in performing other tasks, such as cleaning, adjusting, resetting, controlling and repairing.

When production is automated and the process is no longer under the direct control of the human being, the risk of unexpected machine movements increases. Most operators who work with groups or lines of inter-linked machines have experienced such unexpected machine movements. Many automation accidents occur as a result of just such movements. An automation accident is an accident in which the automatic equipment controlled (or should have controlled) the energy giving rise to the injury. This means that the force which injures the person comes from the machine itself (e.g., the energy of a machine movement). In a study of 177 automation accidents in Sweden, it was found that injury was caused by the “unexpected start” of a part of a machine in 84% of cases (Backström and Harms-Ringdahl 1984). A typical example of an injury caused by a computer-controlled machine movement is shown in figure 2.

Figure 2. A typical example of an injury caused by a computer-controlled machine movement

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One of the studies referred to above (Backström and Döös 1995) showed that automatically controlled machine movements were causally linked to longer periods of sick leave than injuries due to other kinds of machine movements, the median value being four times higher at one of the workplaces. The injury pattern of automation accidents was similar to that for other machine accidents (mainly involving hands and fingers), but the tendency was for the former kind of injuries to be more serious (amputations, crushes and fractures).

Computer control, like manual, has weaknesses from the perspective of reliability. There is no guarantee that a computer program will operate without error. The electronics, with their low signal levels, may be sensitive to interference if not properly protected, and the consequences of resultant failures are not always possible to predict. Furthermore, programming changes are often left undocumented. One method used to compensate for this weakness is, for example, by operating “double” systems in which there are two independent chains of functional components and a method for monitoring such that both chains display the same value. If the systems display different values, this indicates a failure in one of them. But there is a possibility that both chains of components may suffer from the same fault and that they both can be put out of order by the same disturbance, thereby giving a false positive reading (as both systems agree). However, in only a few of the cases investigated has it been possible to trace an accident to computer failure (see below), despite the fact that it is common for a single computer to control all the functions of an installation (even the stopping of a machine as a result of the activation of a safety device). As an alternate, consideration may be given to providing a tried-and-tested system with electro-mechanical components for safety functions.

Technical Problems

In general, it can be said that a single accident has many causes, including technical, individual, environmental and organizational ones. For preventive purposes, an accident is best looked at not as an isolated event, but as a sequence of events or a process (Backström 1996). In the case of automation accidents, it has been shown that technical problems are frequently part of such a sequence and occur either at one of the early stages of the process or close to the injury event of the accident. Studies in which technical problems involved in automation accidents have been examined suggest that these lie behind 75 to 85% of the accidents. At the same time, in any specific case, there are usually other causes, such as those of an organizational nature. Only in one-tenth of cases has it been found that the direct source of the energy giving rise to an injury could be attributed to technical failure—for example, a machine movement taking place despite the machine’s being in the stop position. Similar figures have been reported in other studies. Usually, a technical problem led to trouble with the equipment, so that the operator had to switch tasks (e.g., to re-position a part that was in a crooked position). The accident then occurred during the implementation of the task, prompted by the technical failure. A quarter of the automation accidents were preceded by a disturbance in the materials flow such as a part becoming stuck or getting into a crooked or otherwise faulty position (see figure 3).

Figure 3. Types of technical problems involved in automation accidents (number of accidents =127)

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In a study of 127 accidents involving automation, 28 of these accidents, described in figure 4, were further investigated to determine the types of technical problems which were involved as causal factors (Backström and Döös, in press). The problems specified in the accident investigations were most frequently caused by jammed, defective or worn-out components. In two cases, a problem was caused by a computer-program error, and in one by electromagnetic interference. In more than half of the cases (17 out of 28), faults had been present for some time but not remedied. Only in 5 of the 28 cases where a technical failure or deviation was referred to, had the defect not manifested itself previously. Some faults had been repaired only to reappear later. Certain defects had been present right from the time of installation, while others resulted from wear and the impact of the environment.

The proportion of automation accidents occurring in the course of the correction of a disturbance to production comes to between one-third and two-thirds of all cases, according to most studies. In other words, there is general agreement that handling production disturbances is a hazardous occupational task. The variation in the extent to which such accidents occur has many explanations, among them those related to the type of production and to how occupational tasks are classified. In some studies of disturbances, only problems and machine stops in the course of regular production have been considered; in others, a wider range of problems have been treated—for example, those involved in the setting up of work.

A very important measure in the prevention of automation accidents is to prepare procedures for removing the causes of production disturbances so that they are not repeated. In a specialized study of production disturbances at time of accident (Döös and Backström 1994), it was found that the most common task to which disturbances gave rise was the freeing or the correcting of the position of a work piece that had become stuck or wrongly placed. This type of problem initiated one of two rather similar sequences of events: (1) the part was freed and came into its correct position, the machine received an automatic signal to start, and the person was injured by the machine movement initiated, (2) there was not time for the part to be freed or repositioned before the person was injured by a machine movement that came unexpectedly, more quickly or was of greater force than the operator expected. Other disturbance-handling involved prompting a sensor impulse, freeing a jammed machine part, carrying out simple kinds of fault tracing, and arranging for restart (see figure 4).

Figure 4. Type of disturbance handling at time of accident (number of accidents =76)

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Worker Safety

The categories of personnel which tend to be injured in automation accidents depend on how work is organized—that is, on which occupational group performs the hazardous tasks. In practice, this is a matter of which person at the workplace is assigned to deal with problems and disturbances on a routine basis. In modern Swedish industry, active interventions are usually demanded from the persons operating the machine. This is why, in the previously mentioned vehicle-manufacturing workplace study in Sweden (Backström and Döös, accepted for publication), it was found that 82% of the people who sustained injuries from automated machines were production workers or operators. Operators also had a higher relative accident frequency (15 automation accidents per 1,000 operators per year) than maintenance workers (6 per 1,000). The findings of studies which indicate that maintenance workers are more affected are at least partly to be explained by the fact that operators are not allowed to enter machining areas in some companies. In organizations with a different type of task distribution, other categories of personnel—setters, for example—may be given the task of solving any production problems that arise.

The most common corrective measure taken in this connection in order to raise the level of personal safety is to protect the person from hazardous machine movements by using some kind of safety device, such as machine guarding. The main principle here is that of “passive” safety—that is, the provision of protection that does not require action on the part of the worker. It is, however, impossible to judge the effectiveness of protective devices without very good acquaintance with the actual work requirements at the machine in question, a form of knowledge which is normally possessed only by machine operators themselves.

There are many factors that can put even what is apparently good machine protection out of action. In order to perform their work, operators may need to disengage or circumvent a safety device. In one study (Döös and Backström 1993), it was found that such disengagement or circumvention had taken place in 12 out of 75 of the automation accidents covered. It is often a matter of the operator’s being ambitious, and no longer willing to accept either production problems or the delay to the production process involved in correcting disturbances in accordance with instructions. One way of avoiding this problem is to make the protective device imperceptible, so that it does not affect the pace of production, product quality or task performance. But this is not always possible; and where there are repeated disturbances to production, even minor inconveniences can prompt people not to utilize safety devices. Again, routines should be made available to remove the causes of production disturbances so that these are not repeated. A lack of a means of confirming that safety devices really function according to specifications is a further significant risk factor. Faulty connections, start signals that remain in the system and later give rise to unexpected starts, build-up in air pressure, and sensors that have come loose may all cause failure of protective equipment.

Summary

As has been shown, technical solutions to problems may give rise to new problems. Although injuries are caused by machine movements, which are essentially technical by nature, this does not automatically mean that the potential for their eradication lies in purely technical factors. Technical systems will continue to malfunction, and people will fail to handle the situations to which these malfunctions give rise. The risks will continue to exist, and can be held in check only by a wide variety of means. Legislation and control, organizational measures at individual companies (in the form of training, safety rounds, risk analysis and the reporting of disturbances and near accidents), and an emphasis on steady, ongoing improvements are all needed as complements to purely technical development.

 

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Contents

Preface
Part I. The Body
Part II. Health Care
Part III. Management & Policy
Part IV. Tools and Approaches
Part V. Psychosocial and Organizational Factors
Part VI. General Hazards
Part VII. The Environment
Part VIII. Accidents and Safety Management
Accident Prevention
Audits, Inspections and Investigations
Safety Applications
Resources
Safety Policy and Leadership
Safety Programs
Part IX. Chemicals
Part X. Industries Based on Biological Resources
Part XI. Industries Based on Natural Resources
Part XII. Chemical Industries
Part XIII. Manufacturing Industries
Part XIV. Textile and Apparel Industries
Part XV. Transport Industries
Part XVI. Construction
Part XVII. Services and Trade
Part XVIII. Guides

Safety Applications Additional Resources

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Safety Applications References

Arteau, J, A Lan, and J-F Corveil. 1994. Use of Horizontal Lifelines in Structural Steel Erection. Proceedings of the International Fall Protection Symposium, San Diego, California (October 27–28, 1994). Toronto: International Society for Fall Protection.

Backström, T. 1996. Accident risk and safety protection in automated production. Doctoral thesis. Arbete och Hälsa 1996:7. Solna: National Institute for Working Life.

Backström, T and L Harms-Ringdahl. 1984. A statistical study of control systems and accidents at work. J Occup Acc. 6:201–210.

Backström, T and M Döös. 1994. Technical defects behind accidents in automated production. In Advances in Agile Manufacturing, edited by PT Kidd and W Karwowski. Amsterdam: IOS Press.

—. 1995. A comparison of occupational accidents in industries with of advanced manufacturing technology. Int J Hum Factors Manufac. 5(3). 267–282.

—. In press. The technical genesis of machine failures leading to occupational accidents. Int J Ind Ergonomics.

—. Accepted for publication. Absolute and relative frequencies of automation accidents at different kinds of equipment and for different occupational groups. J Saf Res.

Bainbridge, L. 1983. Ironies of automation. Automatica 19:775–779.

Bell, R and D Reinert. 1992. Risk and system integrity concepts for safety related control systems. Saf Sci 15:283–308.

Bouchard, P. 1991. Échafaudages. Guide série 4. Montreal: CSST.

Bureau of National Affairs. 1975. Occupational Safety and Health Standards. Roll-over Protective Structures for Material Handling Equipment and Tractors, Sections 1926, 1928. Washington, DC: Bureau of National Affairs.

Corbett, JM. 1988. Ergonomics in the development of human-centred AMT. Applied Ergonomics 19:35–39.

Culver, C and C Connolly. 1994. Prevent fatal falls in construction. Saf Health September 1994:72–75.

Deutsche Industrie Normen (DIN). 1990. Grundsätze für Rechner in Systemen mit Sicherheitsauffgaben. DIN V VDE 0801. Berlin: Beuth Verlag.

—. 1994. Grundsätze für Rechner in Systemen mit Sicherheitsauffgaben Änderung A 1. DIN V VDE 0801/A1. Berlin: Beuth Verlag.

—. 1995a. Sicherheit von Maschinen—Druckempfindliche Schutzeinrichtungen [Machine safety—Pressure-sensitive protective equipment]. DIN prEN 1760. Berlin: Beuth Verlag.

—. 1995b. Rangier-Warneinrichtungen—Anforderungen und Prüfung [Commercial vehicles—obstacle detection during reversing—requirements and tests]. DIN-Norm 75031. February 1995.

Döös, M and T Backström. 1993. Description of accidents in automated materials handling. In Ergonomics of Materials Handling and Information Processing at Work, edited by WS Marras, W Karwowski, JL Smith, and L Pacholski. Warsaw: Taylor and Francis.

—. 1994. Production disturbances as an accident risk. In Advances in Agile Manufacturing, edited by PT Kidd and W Karwowski. Amsterdam: IOS Press.

European Economic Community (EEC). 1974, 1977, 1979, 1982, 1987. Council Directives on Rollover Protection Structures of Wheeled Agricultural and Forestry Tractors. Brussels: EEC.

—. 1991. Council Directive on the Approximation of the Laws of the Member States relating to Machinery. (91/368/EEC) Luxembourg: EEC.

Etherton, JR and ML Myers. 1990. Machine safety research at NIOSH and future directions. Int J Ind Erg 6:163–174.

Freund, E, F Dierks and J Roßmann. 1993. Unterschungen zum Arbeitsschutz bei Mobilen Rototern und Mehrrobotersystemen [Occupational safety tests of mobile robots and multiple robot systems]. Dortmund: Schriftenreihe der Bundesanstalt für Arbeitsschutz.

Goble, W. 1992. Evaluating Control System Reliability. New York: Instrument Society of America.

Goodstein, LP, HB Anderson and SE Olsen (eds.). 1988. Tasks, Errors and Mental Models. London: Taylor and Francis.

Gryfe, CI. 1988. Causes and prevention of falling. In International Fall Protection Symposium. Orlando: International Society for Fall Protection.

Health and Safety Executive. 1989. Health and safety statistics 1986–87. Employ Gaz 97(2).

Heinrich, HW, D Peterson and N Roos. 1980. Industrial Accident Prevention. 5th edn. New York: McGraw-Hill.

Hollnagel, E, and D Woods. 1983. Cognitive systems engineering: New wine in new bottles. Int J Man Machine Stud 18:583–600.

Hölscher, H and J Rader. 1984. Mikrocomputer in der Sicherheitstechnik. Rheinland: Verlag TgV-Reinland.

Hörte, S-Å and P Lindberg. 1989. Diffusion and Implementation of Advanced Manufacturing Technologies in Sweden. Working paper No. 198:16. Institute of Innovation and Technology.

International Electrotechnical Commission (IEC). 1992. 122 Draft Standard: Software for Computers in the Application of Industrial Safety-related Systems. IEC 65 (Sec). Geneva: IEC.

—. 1993. 123 Draft Standard: Functional Safety of Electrical/Electronic/Programmable Electronic Systems; Generic Aspects. Part 1, General requirements Geneva: IEC.

International Labour Organization (ILO). 1965. Safety & Health in Agricultural Work. Geneva: ILO.

—. 1969. Safety and Health in Forestry Work. Geneva: ILO.

—. 1976. Safe Construction and Operation of Tractors. An ILO Code of Practice. Geneva: ILO.

International Organization for Standardization (ISO). 1981. Agricultural and Forestry Wheeled Tractors. Protective Structures. Static Test Method and Acceptance Conditions. ISO 5700. Geneva: ISO.

—. 1990. Quality Management and Quality Assurance Standards: Guidelines for the Application of ISO 9001 to the Development, Supply and Maintenance of Software. ISO 9000-3. Geneva: ISO.

—. 1991. Industrial Automation Systems—Safety of Integrated Manufacturing Systems—Basic Requirements (CD 11161). TC 184/WG 4. Geneva: ISO.

—. 1994. Commercial Vehicles—Obstacle Detection Device during Reversing—Requirements and Tests. Technical Report TR 12155. Geneva: ISO.

Johnson, B. 1989. Design and Analysis of Fault Tolerant Digital Systems. New York: Addison Wesley.

Kidd, P. 1994. Skill-based automated manufacturing. In Organization and Management of Advanced Manufacturing Systems, edited by W Karwowski and G Salvendy. New York: Wiley.

Knowlton, RE. 1986. An Introduction to Hazard and Operability Studies: The Guide Word Approach. Vancouver, BC: Chemetics.

Kuivanen, R. 1990. The impact on safety of disturbances in flexible manufacturing systems. In Ergonomics of Hybrid Automated Systems II, edited by W Karwowski and M Rahimi. Amsterdam: Elsevier.

Laeser, RP, WI McLaughlin and DM Wolff. 1987. Fernsteurerung und Fehlerkontrolle von Voyager 2. Spektrum der Wissenshaft (1):S. 60–70.

Lan, A, J Arteau and J-F Corbeil. 1994. Protection Against Falls from Above-ground Billboards. International Fall Protection Symposium, San Diego, California, October 27–28, 1994. Proceedings International Society for Fall Protection.

Langer, HJ and W Kurfürst. 1985. Einsatz von Sensoren zur Absicherung des Rückraumes von Großfahrzeugen [Using sensors to secure the area behind large vehicles]. FB 605. Dortmund: Schriftenreihe der bundesanstalt für Arbeitsschutz.

Levenson, NG. 1986. Software safety: Why, what, and how. ACM Computer Surveys (2):S. 129–163.

McManus, TN. N.d. Confined Spaces. Manuscript.

Microsonic GmbH. 1996. Company communication. Dortmund, Germany: Microsonic.

Mester, U, T Herwig, G Dönges, B Brodbeck, HD Bredow, M Behrens and U Ahrens. 1980. Gefahrenschutz durch passive Infrarot-Sensoren (II) [Protection against hazards by infrared sensors]. FB 243. Dortmund: Schriftenreihe der bundesanstalt für Arbeitsschutz.

Mohan, D and R Patel. 1992. Design of safer agricultural equipment: Application of ergonomics and epidemiology. Int J Ind Erg 10:301–310.

National Fire Protection Association (NFPA). 1993. NFPA 306: Control of Gas Hazards on Vessels. Quincy, MA: NFPA.

National Institute for Occupational Safety and Health (NIOSH). 1994. Worker Deaths in Confined Spaces. Cincinnati, OH, US: DHHS/PHS/CDCP/NIOSH Pub. No. 94-103. NIOSH.

Neumann, PG. 1987. The N best (or worst) computer-related risk cases. IEEE T Syst Man Cyb. New York: S.11–13.

—. 1994. Illustrative risks to the public in the use of computer systems and related technologies. Software Engin Notes SIGSOFT 19, No. 1:16–29.

Occupational Safety and Health Administration (OSHA). 1988. Selected Occupational Fatalities Related to Welding and Cutting as Found in Reports of OSHA Fatality/Catastrophe Investigations. Washington, DC: OSHA.

Organization for Economic Cooperation and Development (OECD). 1987. Standard Codes for the Official Testing of Agricultural Tractors. Paris: OECD.

Organisme professionel de prévention du bâtiment et des travaux publics (OPPBTP). 1984. Les équipements individuels de protection contre les chutes de hauteur. Boulogne-Bilancourt, France: OPPBTP.

Rasmussen, J. 1983. Skills, rules and knowledge: Agenda, signs and symbols, and other distinctions in human performance models. IEEE Transactions on Systems, Man and Cybernetics. SMC13(3): 257–266.

Reason, J. 1990. Human Error. New York: Cambridge University Press.

Reese, CD and GR Mills. 1986. Trauma epidemiology of confined space fatalities and its application to intervention/prevention now. In The Changing Nature of Work and Workforce. Cincinnati, OH: NIOSH.

Reinert, D and G Reuss. 1991. Sicherheitstechnische Beurteilung und Prüfung mikroprozessorgesteuerter
Sicherheitseinrichtungen. In BIA-Handbuch. Sicherheitstechnisches Informations-und Arbeitsblatt 310222. Bielefeld: Erich Schmidt Verlag.

Society of Automotive Engineers (SAE). 1974. Operator Protection for Industrial Equipment. SAE Standard j1042. Warrendale, USA: SAE.

—. 1975. Performance Criteria for Rollover Protection. SAE Recommended Practice. SAE standard j1040a. Warrendale, USA: SAE.

Schreiber, P. 1990. Entwicklungsstand bei Rückraumwarneinrichtungen [State of developments for rear area warning devices]. Technische Überwachung, Nr. 4, April, S. 161.

Schreiber, P and K Kuhn. 1995. Informationstechnologie in der Fertigungstechnik [Information technology in production technique, series of the Federal Institute for Occupational Safety and Health]. FB 717. Dortmund: Schriftenreihe der bundesanstalt für Arbeitsschutz.

Sheridan, T. 1987. Supervisory control. In Handbook of Human Factors, edited by G. Salvendy. New York: Wiley.

Springfeldt, B. 1993. Effects of Occupational Safety Rules and Measures with Special Regard to Injuries. Advantages of Automatically Working Solutions. Stockholm: The Royal Institute of Technology, Department of Work Science.

Sugimoto, N. 1987. Subjects and problems of robot safety technology. In Occupational Safety and Health in Automation and Robotics, edited by K Noto. London: Taylor & Francis. 175.

Sulowski, AC (ed.). 1991. Fundamentals of Fall Protection. Toronto, Canada: International Society for Fall Protection.

Wehner, T. 1992. Sicherheit als Fehlerfreundlichkeit. Opladen: Westdeutscher Verlag.

Zimolong, B, and L Duda. 1992. Human error reduction strategies in advanced manufacturing systems. In Human-robot Interaction, edited by M Rahimi and W Karwowski. London: Taylor & Francis.