روش مبتنی بر تحلیل سلسله مراتبی برای انتخاب وسایل ایمنی ماشین آلات صنعتی

Safe machines make a major contribution to personnel safety on the workplace. Safety of machines is often guaranteed or enhanced by safety devices. The choice of a safety device involves multiple criteria decision making and a ranking of alternatives according to often contrasting performance measures. In this paper, a systematic methodology for selecting safety measures aimed at reducing mechanical hazards of industrial machinery is presented. The method at first includes a classification of mechanical hazards and applicable safety devices, then introduces an exhaustive list of 15 factors useful to judge the suitability of safety devices for comparison purposes. A comparison of relative importance between the rating criteria is then carried out in the framework of the Analytic Hierarchy Process decision making approach, based on expert opinion, allowing unambiguous prioritization of the above decision making factors. This allows a rapid ranking of alternatives and the selection of the most suitable device for a given machine that suits the mission requirements and the preferences of the decision maker. An application example is included to demonstrate the utilization of the method.

Workers are killed or injured as a result of hazardous contact with machinery and equipment. According to NIOSH data, from 1980 to 1998 in the USA occupational injury from machinery was ranked third after motor vehicle and homicide as cause of death, accounting fatalities for approximately 13% of the total. The industry sectors that ranked the highest in injury due to machinery were: agriculture, mining, manufacturing and construction. Similar data are reported even for the other industrialized countries. Some of the leading injuries experienced in these industries were: struck by or against an object, caught in or compressed by equipment, and caught in or crushed in collapsing materials. Safe machines are, therefore, a prerequisite to ensure personnel safety on the workplace. Safety of machines is often guaranteed or enhanced by safety devices. Strict regulations have been enforced in most Countries dictating specific safety requirements to be satisfied by newly built machines or older ones which are to be maintained in service. According to European Union Directives 2006/42/EC and 98/37/EC (superseding previous Directive 89/392/EC) machinery needs to satisfy a number of so called Essential Health and Safety Requirements (EHSRs) contained in Annex I of the Directive. To certify satisfaction of EHSRs, a conformity assessment must be carried out, a “Declaration of Conformity” must be given and the CE marking must be affixed. It is an offence to supply and use machinery not complying with the Directives. This applies to the supply and utilization of new and used machinery and other equipment including safety components. Compliance to Directive can be accomplished by utilizing a hierarchy of methods, namely inherently safe design (to prevent any hazards if possible), adoption of proper safety devices (i.e. Additional Protection Devices, APD), or resorting to Personal Protective Equipment and/or training to contain any residual risk which cannot be dealt with by the above methods. In most cases APDs are adopted given that most operations performed by industrial machinery to process materials are hazardous, unavoidable, and can harm the operator in case he enters in contact with moving parts and working tools. Then the problem of selecting the right safety device arises and involves a number of parties, namely designers and manufacturers of new machines, sellers, renters, buyers and users of new as well as old machines, those modifying a machine to adapt it to new purposes and those upgrading, refurbishing and reconditioning used machines. The EU certification process involves specific penal responsibilities in charge of those issuing the certification. So that the selection of safety device has relevant effects either on workers safety, and on all peoples involved in the machinery acquisition, installation and certification process. Provided that the selection of proper safety devices for industrial machinery is often left to designers of new machines or users of the older ones, the choice is hard given that a vast array of alternative safety devices is available on the market, that many machines are one-of-a-kind and custom-built so that standard choices are often not allowable, and that the installation of an unsuitable device increases risk to workers. This also means that the designer or user can be held liable of any damage caused by an improper selection of safety devices (Baram, 2007). The choice of a safety device, on the other hand, is influenced by many factors, such as cost, reliability, effectiveness, risk of neutralization or new hazards creation, work interference potential and so on. As a consequence, the selection of a safety device involves a multiple criteria decision making and a ranking of competing devices according to often contrasting performance measures. As a contribution to solving this problem in this paper an AHP based approach is thus developed to allow ranking of alternative safety devices, to be used as a decision making tool when selecting the most suitable device for a given machine. The paper is organized as follows. At first the relevance of machine-related injuries is highlighted by presenting statistical data. Then the critical role of design in providing safe machines is outlined. Subsequently a classification of mechanical hazards and risk factors from machinery is provided. Available approaches to risk assessment are then reviewed. A classification of available safety devices is thus carried out to help in screening the set of safety devices in order to define a subset of alternatives to be ranked. Afterwards, the parameters able to characterize any safety devices are also discussed and a set of decision making criteria is defined. Subsequently the AHP methodology for safety devices selection is described. Finally, a numerical example is presented to practically show the capabilities of the method, and a discussion of results concludes the paper.

In this paper the problem of machine safety and safeguarding has been examined in detail. Then the problem of selecting the proper safeguard has been examined. A comprehensive set of problem-specific rating criteria has been defined to compare safeguarding options and AHP has been utilized as a means of providing a consistent ranking of candidate alternatives. This demonstrated how AHP methodology can assist in the selection of safety devices for industrial machinery. Moreover, as a general contribution to the practical applicability of the proposed approach a general purpose pair-wise comparison matrix of rating factors was determined. This allows the user to immediately apply the method, as only the statement of relative rating judgments about case-dependent candidate solutions is left to the analyst. The application example showed that an effective quantitative ranking of candidates can be rapidly obtained using the proposed method. The advantage of the proposed method is not that of avoiding arbitrary or subjective decisions, but rather that of providing an assisted and systematic decision process using consistent rating criteria and consistent evaluations of the alternatives, based on an explicit statement of the decision maker’s subjective preferences. This helps in avoiding much of the guesswork and inconsistency in qualitative and naïve multiple-criteria decision making.