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A design method for product safety MARIAN SCHOONE-HARMSEN



Faculty of Industrial Design Engineering, Delft University of Technology , 9, 2628BX Delft, Jaffalaan, The Netherlands Published online: 27 Mar 2007.

To cite this article: MARIAN SCHOONE-HARMSEN (1990) A design method for product safety, Ergonomics, 33:4, 431-437, DOI: 10.1080/00140139008927147 To link to this article:

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1990, VOL. 33, NO. 4,431-437

A design method for product safety MARIAN SCHOONE-HARMSEN

Faculty of Industrial Design Engineering, Delft University of Technology, Jaffalaan 9, 2628BX Delft, The Netherlands

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Keywords: Design methodology; Product design; Product safety. The Product Safety Method is a method to detect and solve product safety problems.It consistsof two parts, analysisand synthesis. The analysiscan be usedto evaluate products on their safety, bygaininginsight into possibleaccidentswith the product and into criticalfactorsconnectedwitheither the product, the actionsof the user or environmental conditions. The synthesisoffers a structured list of solution strategies for the generation of effective solutions to the detected safety problems. The method may be usedby both ergonomistsand product designers. In conclusion problemsin determiningthe usabilityand effectiveness of the method are discussed as well as how to adapt the method to fit the world of professional design practice.



Attention to safety problems has always been justified because of ethical and human motives. Recently product-liability legislation has added an important economic motive for manufacturers to scrutinize their products' safety. Therefore the product designer or specialist ergonomist will be confronted increasingly with manufacturers' requests to analyze and improve the safety of a product. In some cases this request has been initiated by consumers' complaints or by known accidents with the product. But in general the information available will be insufficient and lacking in the detail necessary to grasp the problem properly. In the case of a new or partly new product information concerning its actual use will be altogether absent (Warne 1982). A usable, systematic method to tackle safety problems effectively will have two important issues to contend with: first, the prediction of ways of using and the connected hazardous situations that might result in accidents; second, to find effective and practical solutions to prevent these accidents.

2. The Product Safety Method The product ergonomics group of the Faculty of Industrial Design Engineering is developing a method that concentrates on product design concerning safety issues. This method is called the Product Safety Method (figure 1). The method is intended to support the product designer when designing products that are safe(r) to use, but it can also be an aid for the ergonomist when analyzing the use of a product. The method reflects a part of the design process and consists of four steps.

2.1. Step 1: Analysis of the problem In most cases, accident information is scarce, so a prediction must be made of possible hazardous situations connected with product use. A conceptual approach to deal with this part of the process is currently available, based on the matrix shown in figure 2. 0014-{)139/90 $)00

© 1990 Taylor & Francis Ltd.

M. Schoone-Harmsen


description of the possible




... product fellUre. (PIP')

... critical prodUCl fealUre. (1")

... selection of a diffelaJl wotlting principle;



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... ICtions of the user (AlA')

-+ environmental

cooditiCilI (SIS')

-+ deactivatiCl'l during the use before damage and injury occurs; -+ separation of the user from the source of danger, ... limilation of the possibililyof modification of Ibe product by Ibe user. influence theactions of the user through the

~ :;'.:"~'F ... environmental critical conditions (S')


-.. safer

product; selection of the user by anthropometric or cognitive characteristics, influence \be selection of the place of use through the product,


" - - - - - - - - - - - - feedback

Figure I.

relevant fadors ... phases In the use


ccnnecsed with prodUCl

situation or ICcept risk

Product Safety Method.

connected with actions

coanected with

of user

situation of use

felch product bring product to place of use make produci rudy for use use product interrupt lask refill product clean product store produci

Figure 2. Product Safety Matrix.

Although designed for use as an analysis tool to make consistent descriptions of known accidents with products (Kanis and Weegels 1990), in this context the matrix may serve to help predict possible situations occurring during the product's use. In order to create a complete picture of the product use many questions have to be answered, such as: which product features play a role when the product is being cleaned?, what actions are necessary to refill the product?, what other articles are stored with the product?, etc. However, a lot of assessment and dedication is needed to cover all relevant situations, places, and ways of using the product and to pose all essential questions.

Design method for product safety


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2.2. Step 2: Identification of critical factors Among the factors found in the analysis, we must identify those which are critical in causing the accident. By changing such a critical factor the product's use can be influenced and made more safe. If a critical factor is related to the product, changing this characteristic may directly lead to safer product use. If, on the other hand, actions or the posture of the user or environmental conditions playa critical role in the hazardous situation, the product designer has to find product characteristics that can be changed to affect these critical factors. Thus the product designer can indirectly influence critical user actions or critical environmental conditions by changing product characteristics. 2.3. Step 3: Synthesis, finding the solution If the problem is well defined as described above, the step to the actual solution of the problem will be a very logical one. According to the aforementioned subdivision, one of the solution strategies may lead to an effective solution. Seven solution strategies are currently available: • to correct a critical product feature (P' ..... Pi:

selection of a different working principle; deactivation during use before damage and injury occurs; separation of the user from the source of danger; limitation of the possibility of modification of the product by the user. • to correct or prevent a critical action of the user (A' ..... A):

influence the actions of the user through the product; selection of the user by anthropometric or cognitive characteristics. • to correct or prevent a critical environmental condition (S' ..... S):

influence the selection of the place of use through the product. Although the systematic approach offered by these solution strategies will be helpful, the skill of a trained product designer is required to develop solution principles into effective and technically feasible product designs. 2.4. Step 4: Evaluation of the effectiveness of solutions The success of a design solution can be defined by a combination of aspects such as producibility, technical functioning, ease of use, service life,psychological performance, etc. In this context, however, it is primarily the effect with regard to the safety of use of the product that has to be measured. Also, restrictions such as safety standards and regulations have to be taken into account in the safety evaluation. The design idea has to reach a certain level of development before predictions of its effect can be made, but evaluating the design at an early stage in the design process offers better possibilities to intervene, where necessary. To perform this analysis the analysis method described above can again be used. This is indicated by the feedback arrow in figure I. If the hazard cannot be eliminated completely the analyst must determine whether or not the remaining hazard is acceptable. If the improvement is not sufficient or the analysis shows new hazards in connection with the product, the whole process can be repeated in order to find a solution that will further eliminate or restrict the hazards. Optimizing the safety aspects


M. Schoene-Harmsen

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of the product will continue as long as the improvements made justify the effort made; economic motives will necessitate the acceptance of a certain level of unsafety. 3. Who can use this method? Until now the method has been used only by students in either projects on product safety or during practical work in industry for graduate projects at the end of their studies. From this it has become clear that becoming familiar with the method is a condition for its successful application. Especially as far as the analysis is concerned; experience with the analysis method is essential. Insight into the relevance of certain factors as well as their critical value will develop with the application of the method for all sorts of products. Confrontation with descriptions of real accidents will contribute to the reliability of the outcome of the analysis. The analysis may well be carried out by a specialist ergonomist. Knowledge of human behaviour in general, including cognition and risk-perception, and more specifically the influence of product characteristics such as colour, shape or weight on the actions of the user is essential. Insight is also required into product failure modes. Further research into these aspects of product ergonomics is needed. Generating solutions, developing- them and weighing up the conflicting requirements are the specific skills of a product designer, required for the synthesis and evaluation of this method. Further experience has to be developed in the indentification of the product features that will, if changed, eliminate the cause of the accident. If a product designer is trained to carry out the analysis of accidents according to the suggested approach and also uses the knowledge gathered to generate solutions and evaluate them, an effective change-over from analysis to synthesis is guaranteed. If on the other hand analysis and synthesis are carried out separately by two different persons, standard presentation of the results of the analysis is important to guarantee the usability of the information for synthesis and evaluation purposes.

4. Applying the method: an illustration The object ofthis example was an ordinary foot-pump (see figure 3). This kind of footpump can be used to inflate the tyres of a car or bicycle, an air-mattress, etc. By pushing down pedal (a) air is compressed in cylinder (b) and forced by way of a rubber hose (e) into the object to be inflated. A metal hook (f) holds the frame parts together for storage.

Figure 3. Foot-pump.

Design method for product safety


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In this case no detailed accident descriptions were available, but a survey of circumstances of use of the pump, including all possible places where it could be stored or used, and of all necessary actions for use, revealed that the unexpected opening of the frame (when the hook slips from the upper part of the frame) was one of the situations most likely to lead to an accident. User actions that may lead to this situation are for instance: carrying the pump by the hook or loosening the hook with one hand without restraining the movement of the frame. The space needed to store the product is also important. Relevant factors connected with the product are: the dimensions of the hook and the force of the spring inside the cylinder that forces back the piston and causes the frame to open. Correction of any of these critical factors may lead to effectivedesign solutions. A few examples are: • optimizing the pump size, making the folding of the pump no longer necessary for storage; • damping the spring energy will cause the frame to open more slowly, however, this may be irritating during use; • disconnecting the cylinder (with piston and spring) from the upper part of the frame, making it possible to fold the pump for storage without forcing the spring out of shape. This last solution may appear to be economically and technically feasible and involves only a relatively small change to the product. Therefore a few solutions in this direction were developed and one of the ideas can be seen in figure 4. After rotating the upper frame part (indicated by arrow 1) the cylinder can be disconnected. Folding is completed by the manipulations indicated by arrows 2 and 3. To make the product ready for use these actions should be conducted the other way round. When evaluating this redesign it is clear that not all safety problems were solved, new hazards may be introduced because of the extra moving parts and because of the possibility of incorrect connection offrame and cylinder before use. It is difficult to give a decisive answer on how to compare the pro's and con's of the redesign.

Figure 4. Redesign idea for the foot-pump.


M. Schoone-Harmsen

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5. Evaluation of the method Until now method improvement has been based on theoretical grounds and on comments from the students who used the method. These comments produced some optimism regarding the usefulness or the method. The solution strategies were considered especially helpful for getting started with the generation or ideas, and in general the method was said to be a good framework for systematic working. Ofcourse this does not guarantee the general applicability or the method, nor its effectiveness. Research is needed to improve both the method's usability and its effectiveness. However, these qualities are difficult to quantify.

5.1. The usability of the method There is no reason to assume that the usability of the method was restricted to certain products, but it was primarily meant for consumer products Ior non-professional use. A serious handicap was the lack or detailed accident descriptions for this kind or product that could serve as a starting point for the analysis. If this missing information is generated as suggested above there is no guarantee whatsoever for completeness and reliability of the facts. Research, already started, must provide adequate ways of gathering the relevant information on accidents and of presenting this information in a useful way to product designers confronted with the task of improving a product's safety, An outline of this research is given by Kanis and Weegels (1990). The same problem occurs if solutions are generated with the help of the solution strategies. The dedication and skill of the designer is the only guarantee that all promising possibilities are checked. With regard to this aspect, research into creativity and the idea-generation process must provide assistance.

5.2. The effectiveness of the method Since the purpose of the product safety method is to help the product designer to design a product in order to make it safe to use, the effectiveness of the method should be measured by the safety of the product use of the newly-designed product. The safety of product use can be understood as the probability of the occurrence of an accident. In fault sequences and risk analysis models probability calculations are made, but most of these models only take into account technical failure leading to unwanted situations (Hammer 1980).Research on construction or component failure has made it possible to quantify the probabilities of technical failures. In theories based on human error attempts are made to estimate the probability of human failure, These estimations are, however, judged to be non-realistic (Wagenaar 1983). Opponents of the human-error theory claim that it is not the user who must be blamed for the mismatch of the product, but the product that should be adapted to the possibilities and restrictions of the user. Looking at accidents with consumer products it is clear that only in a small number of cases is technical failure alone responsible for the accident. User actions, due to the poor adaptation ofthe product to user restrictions, are at least as influential: this form of 'ergonomic failure' was never quantified. In order to be able to say something about the effectiveness of this method, one should measure the improvement in safety after application ofthe method. This means that the safety of product use has measured comparatively.

Design method for product safety


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Research must identify product features that must be changed in order to influence its use, product features that will make the difference between the 'ergonomic success' and the 'ergonomic failure' of a product. 6. Marketing the Product Safety Method The academic world, where this method was developed and tested, differs in many ways from professional design practice. It is not known what information is available to manufacturers and designers regarding the use of their products or regarding accidents with these products. This knowledge may be used to improve the analysis strategy and better adapt it to the information available. Because the Product Safety Method is unknown in the professional world, active marketing is necessary to make it generally accepted. This can be achieved partly through education. Students who have learned to use the method during their training, may continue using it in their professional career. Manufacturers and professional designers can become acquainted with the method by way of the graduate projects, which often take place in industry. Above all, the method must show its economic value, and here the proof of the pudding is in the eating. Active promotion among designers and manufacturers, supported by evidence on the effectiveness and usability of the method is necessary. References HAMMER, W. 1980, Product Safety Management and Engineering (Prentice Hall, Englewood Cliffs, NJ). KANIS, H. and WEEGELS, M. F. 1990, Research into accidents as a design tool, Ergonomics, 33, 439-445. WAGENAAR, W. A. 1983, Menselijk falen, Nederlands Tijdschrift voor Psychologie, 38,209-222. WARNE, C. A. 1982,Designing out accidents-first understand the problem, Applied Ergonomics, 13,2-6.

A design method for product safety.

The Product Safety Method is a method to detect and solve product safety problems. It consists of two parts, analysis and synthesis. The analysis can ...
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