ZEITSCHRIFT FÜR ARBEITSWISSENSCHAFT

Process integration of Virtual Reality in ergonomic evaluation is tested on a specifi c industrial system. Perception of the driver’s workplace depends on the actual driver’s position. The driver’s position is affected by perturbations caused by the system characteristics such as limited realism and modelling accuracy in the Virtual Reality System. The driver’s positions in the Virtual Reality System and in the corresponding real car are compared. The tests are based on the hypothesis that different procedures influence the seat and steering wheel position in Virtual Reality (hypothesis 0). The following hypotheses are tested using different adjustment procedures: Influence of preadjustment without Virtual Reality Visualisation (hypothesis 1): Seat and steering wheel adjustment in Virtual Reality with preadjustment without Virtual Reality Visualisation leads to different positions in comparison to direct adjustment with HMD starting from a neutral position. Influence of preadjustment with human modelling tool (hypotheses 2): Seat and steering wheel adjustment in Virtual Reality with preadjustment using a human modelling tool leads to different positions in comparison to direct adjustment with HMD starting from a neutral position. Preadjustment with eyes shut (hypothesis 3): Seat and steering wheel adjustment in Virtual Reality with preadjustment with shut eyes leads to different positions in comparison to direct adjustment with HMD starting from a neutral position. The comparison of the fi nal seat and steering wheel positions in Virtual Reality with those in the real car shows the deviation of the fi ve procedures. Additional information about influencing effects in Virtual Reality can be seen by comparing the interim values. To validate the procedures the seat and steering wheel positions are compared to the real car: Differences between the procedures and the real car (hypothesis 4): Seat and steering wheel adjustment in Virtual Reality and in the real car lead to similar values. The tests show significant procedural influence on the seat position (hypothesis 0): • Influence of preadjustment without Virtual Reality Visualisation

(hypothesis 1) significant when starting from a neutral position not significant when starting from the simulated position • Influence of preadjustment with human modelling tool (hypothesis 2) not significant with preadjustment without HMD highly significant when using the HMD to perform a direct adjustment • Preadjustment with eyes shut (hypothesis 3) not significant There is no significant influence of the procedures for the steering wheel. Adjustments of the seat and steering wheel starting from a neutral and standardized position using the Virtual Reality Visualisation deliver the best match to a real vehicle (hypothesis 4). The result is based on the system used, but the process is comparable.

Practical Relevance

Objective of the experiments is to find a realistic seating position in Mixed Reality Systems. The result is specific for the system used, but the method can be adopted to other systems. The experiment helps to develop a work procedure for VR used in ergonomic car design.

Contribution of psychological knowledge and methods to the assessment of ADAS

Author: Wolfgang Fastenmeier und Herbert Gstalter

Keywords: Driving task, analysis of behavioural requirements, driver assistance systems, Risk-benefit assessment, HMI (humanmachine interface/driver-vehicle interface)

Summary

Safety problems in car-driving are easily associated with driver errors. Therefore, the classic engineering approach has called for more automation to replace human functions by machines in man-machine systems. But experience in human factors engineering has shown that automation can have disadvantages like deskilling or overconfidence on the side of system users. In car-driving, the idea of assistance has substituted pure automation. The driver is to be supported by information, warnings or interventions, but he can always override the system, thus still being part of the control loop. Assistance systems are nowadays available at all three levels of the driving task. Their development leads to changed task allocations between the driver and the car/system compared to conventional cars. The introduction of the contribution derives somes inferences from this fact. At first, possible problems associated with the introduction of ADAS are mentioned and shortly discussed. A focus of the discussion is the ergonomic design of coded information. The information flow between the driver and the car and its subsystems should be on time, restricted to relevant data, situation specific, acceptable and clearcut. Because of the need for situational adequacy of the information to be presented, the designer should have deeply understood the central role of the driving task in the conception and design of assistance systems. Recently the authors of this article have developped a procedure for analysing driving task requirements (SAFE: Situational analysis of behavioural requirements in driving tasks). It is based on a model of human information processing that is used to model the driver and a taxonomy of driving tasks. The text gives a short summary of the central ideas of the methods and its main procedural steps. The main part of the paper describes the application of the method to evaluate the safety impact of a prototype driver assistance system. The system is composed of a navigation aid and a function to support lane-changing. The driving task under investigation is the approach to a signalised junction including a lane change to the left to prepare a left-turning manoeuvre in the junction. The idea is to model this task using the SAFE-method twice: with and without the assistance system and to compare the resulting requirements for the driver with respect to complexity and risk in the different subtasks. The results show that the assistance system eases the task for the driver. This can clearly be demonstrated in the complexity ratings: Without the system parts of the navigation subtasks are assessed to be medium complex; this assessment is changed to ratings of low complexitiy with the system components. The early announcement of the junction by the system helps to gain time, thus reducing time-pressure linked to various subtasks in the navigation context. Through the redundancy of information in the speech output component, display elements and out of the vehicle information, the accuracy of information intake by the driver is of less importance. The sum of mental requirements is lower with the assistance system. There are less memory and decision processes nesessary, reducing the ratio of conscious to automatic processes. In summary, the complexity of the navigation subtasks in the approach to the intersection is lowered by the system components and the navigation descision is supported in a powerful way. The estimation of risk points into the same direction, based on lower time-pressure with the system. Moreover, less errors are expected with the system. Typical lane change errors like “changing to a wrong lane” or “lane-changing too late” are less probable. After the navigation task has been completed the lane-changing task itself has to be managed. The subtasks related to that phase of the junction approach also gain from the system messages. The ratings of complexity tend to be lower compared to the case without system. Time-pressure and required accuracy of some mental requirements are less critical, e.g. because the system supports diffi cult judgements such as “time gap to car on the left lane too short”. Several demands on driver expectation and memory are eased as well. Whereas the complexity of the subtasks related to the lane-changing manoeuvre is lowered considerably, its riskiness does not change in the two cases. At the end of the contribution some conclusions are drawn. In the framework of the conception and design of ADAS the driver remains the central component of the driver-car-environment system. A reasonable application of an ADAS presupposes a detailed knowledge of the requirements of each driving subtask. The information need of the driver has not only to be determined with respect to its quality, extent and temporal structure, but also the information exchange between the system components has to be optimized to bridge the gulf between the biological system (driver) and the physical system (car). Up to now, there existed no standardized method for a risk-benefit analysis of ADAS. For an early evaluation of prototype system versions the SAFE- method seems to be a very powerful tool. Finally some more applications of the method are reflected.

Practical Relevance

The implementation of ADAS modifies the task allocation between driver and vehicle and therefore changes the mental and psychomotoric driver requirements in task accomplishment. A task analytic approach such as SAFE proves to be useful in a prospective Risk-Benefit analysis of ADAS without having to rely on driver observation and used prior to simulator and field trials. Effects of an ADAS can be listed precisely and appointed to the spatial and temporal structure of the driving task under consideration. Moreover, it may be predisposed as a conceptual design-tool in modelling various variants of HMI-specifications.

How to evaluate safety-critical driver assistance systems? Results of a driving simulator study

Author: Nicola Fricke, Mónica De Filippis und Manfred Thüring

Keywords: Driver assistance system, driving simulator, collision warning

Summary

Evaluation of driver assistance systems mostly focuses on driver distraction which is imposed by the new technology. However, in the case of safety-critical driver assistance such as collision warning systems one should instead use other parameters. As the most important aspect in warning design is whether warnings lead to desired behavior the interesting aspects for evaluation are speed of reaction and appropriateness of actions. Since collision warnings happen to be rare events they should also need hardly any learning. For an ecologically valid investigation of several warning types it is best to use a driving simulator and to assess spontaneous driving behavior. This is reasonable because there does not exist any danger for participants and it is more natural as simple laboratory tests. Investigating in a driving simulator still remains different to field investigations and the conclusions which can be drawn are limited, but relative tendencies between the studied warning types can be assumed and suggestions be made for applications in real cars. Most studies so far concentrated on either laboratory studies or driving simulator studies with instructed tasks. In the reported study 73 participants were continuously driving and confronted with six critical collision scenarios in which collision objects such as car, bicycle and dog could not bee seen by the participants and they were warned before the objects suddenly entered the street. Participants did not receive an instruction on the meaning of the warning. The research question was which warning type would lead to fastest and most appropriate reactions. The investigated independent variable warning type consisted of: spatial sound, spatial tone, simple tone and no-warning condition. Dependent variables consisted of brake-reaction time, distance to collision object, number of collisions and simple reaction pattern analysis. Hypotheses were that the spatial sound warning should lead to fastest reactions, greatest distance to collision object as well as least collisions compared to all other warnings and no-warning condition. In addition all warnings should be better and lead to faster reactions and least collisions compared to no-warning condition. Data analysis consisted of a hypothesesoriented approach combined with post-hoc analysis of the reaction patterns of brake-reactions. Results showed that within scenarios the warning types did not produce much differentiation. Beginning in scenario three, there was an effect for all warnings leading to faster reactions and more distance to collision object compared to no-warning condition. In scenario one this effect was only a tendency and in scenario two only the spatial tone led to improved reactions. For number of collisions there were some differences in the first scenario: simple tone warning led to fewest collisions (50%), all warnings together (57,4%) produced fewer collisions than the no-warning condition (78,9%). Analysis of brake-reactions showed that many people braked before they could see the collision object (starting in scenario 2). Therefore participants were divided into groups of people who reacted before and after the collision object could be seen. This revealed the tendency that most reactions before the object was in sight happened in the toneconditions whereas most reactions after seeing the object took place in the spatial sound condition. In summary a benefit in preventing most collisions existed for the simple tonal warning. In terms of reaction times and distance to collision object there were advantages for the warnings only from the third scenario on and for all conditions compared to the no-warning condition. In contrast to these findings the tone conditions produced very strong reactions which persisted throughout all scenarios and starting in the second scenario most reactions happened before participants could see the collision object. Since this was the time when a learning effect had taken place one has to question whether this behavior is appropriate at all times. If traffic is following very closely for example, such fast reactions without evaluation of the surrounding environment can be dangerous. The spatial sound condition led to most reactions after the collision object could be seen and one can assume that this behavior is more reasonable and the warnings might prepare people for the execution of the correct response. This assumption should be tested in further studies. Concluding, it can be helpful to not just evaluate such systems using well-known driving parameters but adding behavior-analyses as well. It is anyhow most important to assess spontaneous driving behavior for a realistic and reasonable evaluation of safety-critical driver assistance systems.

Practical Relevance

The paper addresses the evaluation of critical driver assistance systems through assessment of spontaneous driving behaviour in a driving simulator. Besides traditional variables such as brake-reaction time and number of collisions a simple reaction pattern analysis is introduced as well. The human factors practitioner gains insights in the design and evaluation of collision warnings as an example for critical driver assistance systems through discussion and presentation of the study and its results.

A Master-controller to help driving locomotives and multiple units devoted to cross-border traffic

Author: Manfred Rentzsch, Denis Seliger

Keywords: Railway traffic, Ergonomics, Driver´s desk, Mastercontroller

Summary

With a view to promoting cross-border railway operations, a driver´s desk has been developed that, thanks to its modular structure, can be flexibly adapted for use in different locomotives, multiple units, etc.. An integrated controller for both traction and braking including the vigilance button – the so-called Mastercontroller – ensures safe and effective driving of the railway vehicles. This multifunctional driving assistance system as part of the driver´s desk was tested by engine drivers of different European countries. The extensive functional and integration tests as well as a preliminary study were followed by the performance and acceptance tests, using the demonstrator in a virtual demonstrator environment provided by Siemens. It was not practical to carry out tests with more than five drivers from each railway company, so those selected were ones with at least ten years´ professional experience overall or have had experience of driving trains across national borders. A total of 39 experienced drivers from six European countries took part in the tests. The test group included drivers of different statures (ranging from 160 to 202 cm), which made possible to use the mock-up variants for an ergonomic appraisal depending on body height. In order to ensure that all the test drivers started from the same position, they were prepared by means of extensive documentation beforehand. Extensive data was collected during the tests by means of questionnaires, final interviews in a structured form, visualized data, computerized tachograph data and stress scales. Two different variants of the integrated traction/ braking controller were created during the development phase. These are: The mono master controller, which is comprised of a single set-point adjuster moving through a radial trajectory, The duo master controller, which is comprised of two sliding set-point adjusters very close to one another and moving in parallel. In an initial series of tests, the demonstrator was tried out by thirty test drivers, who had to drive a locomotive (hauling a freight train) and a multiple unit over a virtual conventional railway line. In a second series of tests, nine drivers had the opportunity trying out the functional configuration of an ICE train set firstly with a reduced duo master controller and secondly with a mono master controller in a virtual high-speed environment. The Mastercontroller and the Industrial Design of the drivers desk were evaluated positively and accepted by the drivers. One of the findings to emerge from questioning the engine drivers from the various European countries was that about three quarters of them considered it advantageous to have the traction and braking functions integrated in a master controller. The single-handed control of the locomotive, multiple unit, etc. with an integrated traction/braking controller positioned to the driver´s right turned out to be suitable solution for both heavy freight trains and multiple units. The functionally based grouping of the control elements and their arrangement on the console ensures that drivers will quickly understand the operating concept. The test participants welcomed the dual use of the terminals as both displays and control elements as a forward-looking solution. As regards the actual display (light-density contrasts) and the information content (the total amount and the menu-based navigation), it was considered that there is still scope for further development and improvements. The demonstrator and the industrial-design mock-up are well designed for both small individuals (arrangements of the controls and monitors) and taller one (leg room). For ergonomic reasons, it is recommended that the driver´s desk has to be constructed so that their height can be varied (footrest and working surface), since that guarantees that it will be possible for a wide group of users to adjust the conditions for driving trains, either seated or standing, which helps combat premature fatigue.

One of the project´s other objectives was to obtain assured ergonomic and technical findings for recommending their inclusion in UIC leaflet 651 “Layout of driver´s cabs in locomotives,

multiple unit trains and driving trailers.

Practical Relevance

A driver´s desk for railway vehicles, which is suitable for cross-border traffic and which enables an optimal strain of the engine driver, has been developed and tested successfully. Further on assured ergonomic and technical findings were derived for recommending their inclusion in an UIC leaflet regarding the design of driver´s cabs in locomotives and multiple unit trains.

Vol. 2 - 2008

Integration of ergonomic aspects within a lifecycle oriented product management

Author: Klaus J. Zink, Dunja B. Eberhard

Keywords: Product Ergonomics, Production Ergonomics, Product Development, Product Lifecycle, Product Management

Summary

The competitive advantage of a company depends – among other variables – on the effi ciency and effectivity of employees and structures and how quickly necessary adjustments can be accomplished. Product development as a knowledge-intensive area plays a crucial role for competitiveness of enterprises. The integration of Human Factors or Ergonomics in the planning of work systems starts with the product development process. Such an understanding implies new challenges in regard of integrating ergonomic aspects in the product development process as well as connecting product development with the work systems design process. In the recent discussion about product development infl uences of the work systems design play hardly any role, although it is precisely the creativity and motivation of the employees that form the product development process. Therefore the design of organizational structures has to consider these facts. So far, traditional concepts of product development focus purely on technical and economic aspects of the product, whereas the ecological and social dimensions are not considered with a similar weight. The concept of lifecycle oriented product management referring to Ergonomics demands to design and manufacture products in such a way that companies meet (and sometimes exceed) the expectations of the customers – especially concerning usability criteria. This is in a certain contrast to the use of ergonomic knowledge in today’s product and process design. There are several causes for not having used ergonomic knowledge in the past: Departments of Ergonomics had to be given up during lean management strategies or are not existing. There seems to be a wrong belief that cost effi cient manufacturing does not need Ergonomics. This may be caused by the fact that respective business cases are not known. Other arguments can be reasoned by time pressure, especially because of reduced product innovation cycles. This behavior leads to a poor ergonomic quality of products and work systems. From an Ergonomics point of view a lifecycle oriented product management seeks for an added value for products and work system design. First of all, this task is related to the two primary objectives of Ergonomics: To seek to enhance the effectiveness and effi ciency of work systems, and secondly, to satisfy customers’ and employees’ needs. The last one can be measured by the usability of products and the overall quality of (working) life. Within a lifecycle oriented product management Ergonomics has several tasks: To build up a relationship between product design and work system design (especially for assembly, maintenance and repair, and disassembly of the product), as well as the usability of the product for the customer (user of the product). Usability is a relevant aspect, not only for the end-user – but also for employees in respective work systems to realize effi cient and ergonomically acceptable working conditions. Strategies for the integration of ergonomic aspects within an integrated product management can be evaluated by four criteria: time of integration, method of integration, area of integration and focus of integration („product“ Ergonomics and „production“ Ergonomics). Ergonomic aspects in production (including assembly) again affect the work system respectively the work content design. In many production plants, the assembly is an important organizational unit that ties extensive personnel capacity together. In this context negative impacts like absenteeism, employee turn-over, and quality problems are important cost drivers. Therefore, a more interesting work content combined with social identifi cation within small (self managing working) groups could be a helpful solution to reduce negative impacts. Whether such groups can be realized or not also depends on the structure of the product itself (e.g. modular design). Insofar, those questions have to be part of the product development. Structural changes not only require small organizational units with a stronger object- respectively process-orientation, but also a thinking in customer-supplierrelationships. This cannot be gained by only extending the work content, but also by creating cross-functional networks. By integrating the design of the work content within production respectively assembly in the product development process not all relevant design goals are included. Thus, the specific ergonomic goal (adjustment of working conditions to human characteristics and capabilities) has to be realized in designing the production system. Any design solution should be evaluated based on three quality factors: effi ciency, effectiveness, and humanity. The discussion shows that the integration of product development and lifecycle oriented process development into a new understanding of product management is able to create win-win-situations. On the one hand, better products will create competitive advantages. Herewith the sales aspect is focused. Additionally, companies realize corporate social responsibility in creating better working conditions by designing work systems with a more demanding (and interesting) work content. This may lead to a growing reputation within and outside the enterprise.

Pracical Relevance

The European Union has recently defi ned new legal requirements as part of its sustainability policy regarding the recycling or disposal of products. The technical quality of products has been increasing more and more during the last years – therefore there is a need for further features to be successful in global competition. This development also demands from compa-nies to design and manufacture their products in a way that they meet the expectations of their customers – in a society that is getting older – especially in relation to usability.

The Software Incarnate: Digital Human Models for CAx- and PLMSystems

Author: Jens Mühlstedt, Hans Kaußler, Birgit Spanner-Ulmer

Keywords: Digital Human Models, Computer Aided Design (CAD, CAx), Product Lifecycle Management (PLM), Product Design, Process Design

Summary

Introduction

Digital human models are important tools for product and process design. This paper describes state of the art models used within CAx- or PLM-Systems. Digital human models are three-dimensional, exemplary, virtual reproductions of real humans. Since the 1960es many different models have been developed, for example BoeMan (Ryan, Springer 1969), Safework (Safework Inc. 2000) or Tempus (Kroemer et. al. 1988; Badler et. al. 1985). Initially these models were two-dimensional digital copies of anthropometric templates. Issues of industrial companies or universities pushed the development and over the years they reached a number of functionalities and applications.

State of the Art

The product lifecycle management software Tecnomatix (Siemens/UGS) is using a model called eM-Human. In the past years this meant the AnySim-model, which has been replaced by the Jack-Model in version 8.1. For major use in the digital factory eM-Human is able to do ergonomical and time analyses, i.e. posture analysis, reachability, visibility, MTM / time analysis). The Jack-model was developed at the University of Pennsylvania together with the NASA and Transom Technologies Inc. The initally Tempus called model is now owned by Siemens/UGS. With 68 joints and 135 degrees of freedom a number of analyses can be done (i.e. force analyses, push/ pull- or lift/carry-analyses). In addition to eM-Human the Ramsis-Model can be used within Tecnomatix, too. Human Builder is the human model for Catia, Enovia and Delmia from Dassault Systemes. It uses 148 degrees of freedom and 99 joints. The anthropometry can be customized, different activity and posture analyses are available and working tasks can be simulated. The german model RAMSIS (from Human Solutions) was developed by the University of Eichstätt, the Technische Universität München, the company techmath and some automotive manufacturers. Thus, it is used mainly for automotive, aircraft and industrial vehicle issues. The model uses 53 joints and 104 degrees of freedom. Analyses of comfort, visibility and reachability surveys and force analyses can be done. Beside anthropometrical databases the scans of 3D-body-scanner can be imported to form a model. An interface to virtual reality software is also available. The model Santos is used in the Virtual Soldier Research Program of the University of Iowa. It uses accurate biomechanics with models of muscels, deformable skin and the simulation of vital signs. With these systems analyses of fatigue, discomfort, force or strength can be done. Furthermore modules for clothing simulation, artifi cial inteligence and virtual reality integration are available for the real-time system. Some other models like the Boeing Human Modeling System (BHMS) or the System for Aiding Man-Machine Interaction Evaluation (SAMMIE), complete this listing. Many problems are solved with nowadays digital human models. Nevertheless, there are many issues which in the future can be integrated in the existing or in new models.

Practical Relevance

Companies and universities use and plan to increasingly use digital human models. This paper compares the most important state of the art models. Practical hints for the use of the models are given.

Personal goals, organizational goals and indicators of job strain

Author: Klaus-Helmut Schmidt, Barbara Neubach

Keywords: Person-organization-fit, goal divergence, burnout

Summary

The concept of personal goals has been developed by social and motivational psychologists to analyze people’s feelings, thoughts, and actions in natural contexts. Personal goals can be defined as future-oriented representations of what individuals are striving for in their current life situations and what they seek to attain in various life domains. There is a growing body of evidence to suggest that the successful pursuit of personally meaningful goals represents a major source of psychological well-being. In the majority of studies addressing this issue, respondents were asked to first describe their goals and then to assess them according to a number of attributes. Commitment to goals, attainability of goals, and perceived progress in goal achievement were found to account for interindividual differences in measures of well-being. In contrast, poor conditions to attain personal goals were associated with impaired progress and predicted a decrease in well-being. In work contexts, personal goals have been examined in relations to their fit with the goals of the organization. In general, the fi t between people and the organizations in which they work is defined as the compatibility between people and organizations that occurs when (a) at least one entity provides what the other needs, or (b) they share similar fundamental characteristics, or (c) both. In a recent meta-analyse of corresponding studies, it was found that an increasing fit between personal goals and goals of the organization was associated with an increase in job satisfaction. In contrast, goal divergence resulted in a decrease in job satisfaction. However, evidence is lacking so far whether goal divergence exerts unique influences on measures of well-being. Going beyond bivariate relationships observed in previous studies, in the present study goal divergence was investigated in combination with well-established forms of work load

(time pressure, task complexity). Furthermore, instead of job satisfaction various indicators of psychological strain were used as criterion measures. Data from 341 staff members of a large civil service organization revealed that goal divergence contributed significant portions of incremental variance to the prediction of psychological strain, over and above that accounted for by the measure of work load. A misfit between personal goals and goals of the organization resulted in an increase in psychological strain. The discriminant validity of these expected relationships was supported by a measure of musculoskeletal complaints which, as an indicator of physical strain, did not reflect comparably strong influences of goal divergence.

Practical Relevance

The adverse effects of goal divergence on indicators of psychological strain suggest certain strategies for improving the fit between personal goals and goals of the organization. This can be achieved by (a) communicating the goals of the organization in the process of personnel recruitment in a clear and understandable way, (b) assessing the personal goal- and value-profi les of job applicants, and (c) promoting organizational socialisation processes which give a precise idea of the organization’s mission and goals.

A validation study of the EFQM Excellence Model from a work psychological perspective

Author: Sylvie Vincent

Keywords: Validation Study, EFQM-Model, Total Quality Management, Industrial Science, Work Psychology

Summary

This study starts from the theorised conceptual connection between Total Quality Management (TQM) and industrial science. This paper asks whether TQM integrates the original concepts from work psychology that target health promotion and personality development as a goal of humane work. The subject of the study presented is the European reference model for the implementation of TQM-strategies of the European Foundation for Quality Management (EFQM). The EFQM Excellence Model is the most widely used framework for total quality self-assessment in Europe (Eskildsen & Dahlgaard 2000; Hakes 1996; McAdam & Welsh 2000; Westlund 2001; Yang et al. 2001). According to the European Foundation for Quality Management, more than 30,000 companies comply with the principles of this model (Tanner 2005). It is emphasised that the model especially focuses on the consideration of employees as the human resources of an organisation (Kämmer et al. 2001; Zink 2004). However, it should be noted that the accentuation of human resources within the EFQM-Model does not automatically imply any special consideration of the employees’ needs for health promotion and personality development in the workplace. What this quality instrument exactly assesses via its employee-oriented criteria remains unexplored. Theoretical papers indicate the relevance of concepts from work psychology as an integral part of the TQM-approach. A conceptual integration of areas of application of industrial psychology into the EFQM-Model is assumed (Wojda & Hacker 1995; Zink 1995b, 2004). Due to the fact that this theoretical foundation lacks empirical evidence, this assumption turns out to be problematic. It is apparent that the employee-related criteria constitute, from a quantitative perspective, a considerable part of the model. It remains unclear what they actually measure as regards content, and whether they integrate concepts of health promotion and personality development. Within the framework of this study, the EFQM Excellence Model is considered in its function as an instrument for organisational diagnosis. The research objectives are to identify the constructs that form the basis of the employee-oriented criteria of the EFQM-Model, and to empirically verify their construct validity. The rationale behind this approach is to identify which constructs are effectively measured in practice. The analysis is carried out under the hypothesis that the holistic quality model of the EFQM can be regarded as an organisational diagnosis instrument that measures original work psychological concepts that integrate health promotion and personality development in the workplace with the intention of improving the quality of working life. To verify the conceptual connection between the content of work psychology and the employee-related criteria of the EFQM-Model postulated in theoretical papers, a step-by-step methodological approach was chosen which combines qualitative and quantitative research techniques. At first it was necessary to explore what exactly the EFQM instrument measures regarding its employee-oriented criteria. The EFQM-interview-guideline was analysed by content. By means of the structuring qualitative content analysis (Mayring 2007), the employee-related aspects were assigned to theoretically founded categories based on theoretical constructs of work psychology. In order to prove the validity of the identified underlying constructs empirically, an analogue quantitative survey instrument was developed by assembling scales from validated and evaluated work psychological instruments according to the extracted categories. The data collection included a qualitative and a quantitative survey. The analysis was based on interviews pertaining to the EFQM criteria “leadership” and “employee orientation”. The interviews were conducted among 25 employees of a Transport and Logistics Company in Switzerland. Subsequently the subjects completed the analogue questionnaire. This quantitative instrument fulfilled the function as external criterion. A comparison of the results of the interviews with the results of the questionnaire should give information regarding the construct validity of the categories. The juxtaposition of the quantitative and qualitative data requires a quantification of the EFQM-interview-data, which was realised through scaling structuring (Mayring 2007). In order to asses the construct validity, an analysis of the Mulitrait-Multimethod-Matrix by Campbell and Fiske (1959) was conducted. An analysis of the Multitrait-Multimethod-Matrix reveals that the criterion of the convergent validity is fulfi lled and that the criteria of the discriminant validity are also tendentially confirmed. These results indicate that industrial scientific concepts do constitute an integral component of the model. Consequently, the EFQM-Model, in its function as an analytical tool, has the potential to adequately contribute to health promotion and personality development in the work environment.

Practical Relevance

The results show that the model supports the requirement that health-related interventions should be integrated in holistic management systems. The analysis of the EFQM-Model discloses that the model is an appropriate tool for this purpose, since it is considered to be an “integrative management system“ and encompasses concepts of health promotion and personality development. In addition, these results warrant the conclusion that the synthesis of work psychology and TQM releases synergetic potential through the integration of work psychological concepts, such as worksite health promotion, in a superior, holistic quality-enhancing approach. Accordingly, holistic total quality frameworks such as the EFQM-Model open up new possibilities for the implementation of health promotion concepts.

Vol. 3 - 2008

Trajectory preview in vehicles by means of contact analogue display: an evaluation using eye movements tracking

Author: Christian Lange and Heiner Bubb

Keywords: Eye-tracking, driver assistance, contact analogue Head-up-Display

Summary

In this work, visual parameters which are related to driver’s distraction and strain are discussed. These parameters can be extracted and afterwards evaluated using eye-tracking. It is also shown how the manual evaluation of visual data can be supported and facilitated by specifically developed software. In presented experiment, results of such eye-tracking data analysis are used to evaluate driver assistance system, which uses head-up-display for presentation of the movement trajectory of a driven car by means of contact-analogue technique.

Pracical Relevance

A method is presented, which allows to evaluate driver assistance systems with the help of eye tracking. Moreover, statistically consolidated, ergonomic findings for the contact analogue version of a driver assistance system are established and presented with the help of this method.

Mapping the distribution of focused visual attention in real 3D space: Potential implications for interface design

Author: Gerhard Rinkenauer and Marc Grosjean

Keywords: Focused attention, flanker compatibility effect, distribution of attention, 3D interface design

Summary

Previous studies suggest that the focus of visual attention, typically investigated with 2D displays, is limited to a certain area of the visual field and shows a central-to-peripheral gradient. In the current study we relied on the flanker interference task to assess the size, shape, and temporal dynamics of the distribution of attention in 3D space. This was achieved by manipulating both the eccentricity and depth of the flankers relative to the target. The amount of flanker interference at the various flanker locations was then used to estimate the gradient of attention at surrounding locations. Based on these estimates, contour plots were created to visualize the distribution of attention. Our results demonstrate that (a) the distribution of attention is limited in depth, (b) the attentional gradient in depth differs from the 2D gradient, and (c) the shape and size of the attentional distribution seems to change over time.

Practical Relevance

The implications of this study are especially relevant for the design of 3D interfaces in which visual information has to be extracted within a glance, such as stereo head-up displays. By relying on the task and statistical techniques employed here, it should be possible to map the distribution of attention in space for any type of 3D display. On this basis, the density of visual information in the display could be adjusted in order to minimize the risk of distraction by other visual signals in the display or environment.

Limitations to miniaturization in CCD – technology

Author: Nicolas Rohner and Roman Boutellier

Keywords: Miniaturization, Optics, CCD, Photography, Technology speed, Technology management

Summary

In modern photography CCD-sensors are the dominant technology for image recording. Big progresses in miniaturization led to this success. But especially in the largest market segment for compact cameras, accounting for over 120 units in 2007, a technological dilemma surfaces. Firstly, picture quality has reached a satisfactory level, making further improvements almost obsolete. Secondly, experience shows that cameras with pixel sizes beyond 3 μm witness loss of picture quality, whereas average pixel size already in 2003 dropped beyond this threshold. New compact cameras often show inferior picture quality compared to their predecessors. This is no new finding for photographers; though this paper shows the severeness of these problems as an industry-wide issue by analyzing technical properties of over 1000 digital cameras since 1996.

Practical Relevance

Product ergonomics considers human skills and customer needs marketing products. But such marketing influence can have negative effects too, as is the case with digital cameras where expectations raised cannot be fulfilled technologically. Technological progress reached a deadlock, this finding is of importance for both the manufacturers and customers. The former ones need to shift their focus in marketing and development in order to create new potential for differentiation. The latter bases his buying criterion on long past and obsolete criteria. Cameras require new measurands substituting for megapixels declaring image quality.

Do multi-view X-ray systems improve X-ray image interpretation in airport security screening?

Author: Claudia Christina von Bastian, Adrian Schwaninger and Stefan Michel

Keywords: Aviation security, display technologies, human machine interaction, object recognition, visual psychophysics, X-ray imaging

Summary

X-ray screening of passenger bags is one of the core elements in aviation security in order to prevent terrorist attacks. Large investments have been made into new technologies, for example in multi-view X-ray systems. Because of several Xrays, multi-view systems provide more than one X-ray image of the same passenger bag and hence present the security screener multiple perspectives of that bag. In this study, we evaluated the benefit of multi-view X-ray systems compared with state-of-the-art single-view X-ray systems. Single- and multi-view X-ray images of passenger bags were presented to 32 novices who had to decide if the bag contained a prohibited item or not. The results show that multi-view X-ray systems lead to a higher detection performance of prohibited items in difficult conditions, such as when it is rotated in a non-canonical manner or superimposed by other objects. Additionally, the results indicate an increase of the reaction time for performing the screener’s task with multi-view in comparison with single-view X-ray systems. A specific training for airport’s security screeners might increase the advantages and reduce the disadvantages of multi-view X-ray systems.

Practical Relevance

Due to increase in global mobility and in security requirements, load caused by security checks in air traffic becomes an important issue. New X-ray scanners enable a multi-view display of luggage in order to facilitate detection of threat objects. Performance and, therefore, strain caused by the security check task depends on the number of presented views. Reduced load can be achieved by means of training detection of threat objects.

Complexity Assessment of Visual Search Processes in Human-Computer Interaction

Author: Christopher Schlick, Carsten Winkelholz, Florian Motz, Sönke Duckwitz and Morten Grandt

Keywords: Visual search for multiple targets, information theory, complexity, navigation information systems

Summary

A quantitative complexity theory of human-computer interaction is presented and validated by means of laboratory experiments. Based on the seminal work of Grassberger in theoretical physics, an information-theoretic complexity measure is introduced. The measure has several advantages with respect to previous approaches. First, it relies solely on information-theoretic quantities such as dynamic entropies, which are intimately connected with the concept of complexity and not randomness. Second, the measure is model independent and can be estimated efficiently from data. Third, the estimates can be derived from behavioral patterns in terms of observable interaction events and do not need subjective ratings or psychophysiological measurements. The validity of the novel measure is studied in experiments of visual search processes with computer-based navigation information systems for modern ship bridges. The experiments were carried out in a high-fidelity marine simulator with 30 participants. The platform motion (with or without motion) and the workplace illumination (800 lux or 30 lux) were varied systematically and the complexity effects of the variation were studied. The results show that the complexity of the visual search processes is significantly lower when the simulator is put in sea state characteristics and the human is facing considerable motion forces. In addition, interaction complexity is significantly lowered when illuminance is reduced from the daylight level of 800 lux to the twilight level of 30 lux. Therefore, the novel complexity theory seems to be a valid approach for the quantitative assessment of visual search processes in human-computer interaction.

Practical Relevance

The contribution presents a quantitative complexity theory of human-computer interaction and introduces an informationtheoretic complexity measure. Both the complexity theory and the measure are useful for the software-ergonomic design and evaluation of interactive computer systems.

Eye-neck/scapular area interactions during strenuous near work – Biologically plausible pathways with relevance for work related musculoskeletal disorders of the neck and upper extremity

Author: Hans O. Richter

Keywords: Accommodation, asthenopia, convergence, musculoskeletal, pain, workplace

Summary

The time honoured dictum “the eyes steer the body” has gained additional legitimacy in recent years with the advent of new mechanisms which link the visual and musculoskeletal system with one another. A systematic review of the circumstances, under which a change in accommodation/ vergence loads actually lead to alterations in physiological levels of musculoskeletal tonus, or vice versa, therefore, appears timely.

Practical Relevance

There is full consensus regarding the vital importance of the visual and musculoskeletal ergonomics of a modern office work (Piccoli, 2003). If both visual and the musculoskeletal aspects are given full and equal weight in the design and evaluation of work places, it is predicted to lead to an improved quality the individual worker, improved productivity and profit for the employer.

Evaluation of progressive lenses by means of a field study

Author: Marino Menozzi, Esther Bergande and Philipp Sury

Keywords: Progressive lenses, vision, presbyopia, lens fitting, lens dispensing

Summary

Amplitude of accommodation decreases with increasing age. This effect, termed presbyopia, reduces the ability to focus objects at near. Since in everyday visual tasks viewing distance varies, a continuous range of powers are required to best compensate for reduced accommodation in elderly. In progressive lenses a continuous range of powers is installed along the vertical. By varying the inclination of gaze, the user of a progressive lens selects an appropriate power. Unfortunately, the advantage of continuous range in powers in progressive lenses comes along with unwanted astigmatisms, which are distributed over the lens. Different designs of progressive lenses are available on the market. Designs differ among other in gradient of power along the vertical and in the topography of unwanted astigmatisms. In order to assess suitability of four different lens designs, we run a field study, in which 105 presbyopic subjects tried all lenses. Each subject tried each lens for three weeks. Objective as well as subjective data were collected during the trial. Statistical analysis revealed a clear distinction in suitability of tested lenses. The lens, in which individual demands and habits are considered, turned out to be the best suitable. In this lens, prescription and therefore the design of the lens considers individual scoring of demands in different sectors of the field of gaze.

Practical Relevance

The results of the study emphasises the role of individual visual preferences in selection of a suitable design of progressive lenses. A careful evaluation of individual preferences is a prerequisite for a successful dispensing of progressive lenses.

A first step on eye movements in office settings

Author: Philipp Sury, Sylvia Hubalek and Christoph Schierz

Keywords: Light, office environment, eye tracking

Summary

There is increasing awareness of the importance of light management for office environments. The positive effects of light on human mood are known for a while already, but in this exploratory study it is examined if an operationalization by gaze shifts results in significant patterns depending on the light source. Eye tracking data was gathered of 24 office workers during their daily routine under four different light conditions. Results show the importance of windows as a primary resting place for the worker‘s gaze when taking a break from computer work.

Practical Relevance

The findings in this study can be seen as a further puzzle piece adding to the already existing DIN EN ISO 9241-6:1999 and DIN EN 12464-1:2003 standards on recommended light design in offices.

Sound protection of musicians according to the new EC Directive 2003/10/EG

Author: Helmut V. Fuchs

Keywords: Musician´s workplace, sound load, ear protection, roomacoustics, acoustical ergonomy, orchestra pit

Summary

In February 2008 a new directive replacing the German UVV “Lärm” of 1997 has established more demanding limits for the noise exposure in musicians (Fallenstein 2007). Employers and employees are, however, confronted here – by contrast to the situation in noisy industrial environments – with a seemingly unsolvable dilemma: On one hand, a reduction of the sound emission at the sources themselves by the necessary 5 to 10 dB(A) according to Table 1 after Hohmann 2007 appears absurd and contra-productive in view of the musical events strived for by the artists and expected by their audiences. On the other hand, a majority of the actors affected refuse to wear personal ear protectors according to Figs. 1 and 2 during the decisive services in the orchestra determining the exposure – for very plausible reasons (Richter et al. 2007). Organisational and conventional sound shielding and damping measures, likewise, cannot solve this problem consistently. In the still escalating conflict between acoustically more and more powerful musical instruments and artistically ambitious musicians on one hand and ergonomic as well as medical requirements on the other a practicable solution was sought and found in constructional measures yielding an amazing sound reduction at the sources themselves (Fuchs 2007 a). For these to become effective it is necessary to acoustically treat the respective working environments in a fundamentally new way (Zha et al. 2002): By reducing the room response especially at the low frequencies, which normally do not even dominate in performance spectra, by means of highly efficient broadband resonance absorbers according to sections 5.3 and 10.1 in Fuchs 2007 b. These can considerably improve the overall working conditions of musicians in spaces like orchestra pits, rehearsal halls, teaching and exercising rooms, refer e.g. to section 11.6.5 in Fuchs 2007 b. They essentially avoid any increase of the reverberation time in the room towards the lower frequencies below 500 Hz as shown on Figs. 6 and 9 – a condition which is very rarely experienced in existing enclosures and which admittedly lacks much of the “resonance”, “envelopment”, “roomliness” and “warmth” traditionally sought after by, in particular, elder listeners of preferably romantic music. By contrast, this alternative room-acoustic concept creates a high acoustic transparency which brings about a better ensemble play with less strain and less unintentionally raised sound emissions according to Fig. 4 thus enabling the required sound reduction mentioned above to be achieved with no deficit in the artistic and emotional results, provided that all musicians conform to a correspondingly thoughtful intonation and their managers to a responsible conducting – especially during rehearsals. Along with thoughtful organisational measures the daily or weekly sound exposure level of musicians can safely be lowered by 5 to 10 dB(A) without a recourse to the very hindering and therefore disliked sound screens after Wogram 2007 (see Figure 3 a) to be placed in the midst of an already densely packed orchestra or ear protectors after Richter et al. 2007 (Figure 1) to be worn by persons already loaded with heavy other burdens. Employers and managers now have two good reasons to embark on constructional improvements at the respective work places: firstly, to improve the environmental conditions for achieving high-level artistic glamour without extraordinary strain and power and, secondly, to protect their employees against unnecessarily high loads of sound exposure and severe risks of hearing damage. Correspondingly refurbished rooms have meanwhile found numerous grateful users: Orchestra pits in Stuttgart, Flensburg (Figure 5), Schleswig, Essen, Koblenz, Rendsburg, Duisburg, Mainz, Aachen, Regensburg, Birmingham, London and Zürich and larger rehearsal rooms in Stuttgart and Mainz according to Figs. 7 and 8 may serve as suitable demonstration projects for this novel approach to a longstanding problem. Clearing the undefined low-frequency rumbling in ill-conditioned music rooms can also improve the room-acoustic quality of auditoria and raise the delight of listeners – even of those who are traditionally accustomed to less articulated bass lines in opera or concert events. A good validation of the new concepts may be found in the “Großes Haus” of the Staatstheater Mainz, which was recently reconstructed as a multi-purpose environment for opera, ballet, concert and theatre events (Fuchs 2007 b, section 11.6.6).

Practical Relevance

The new EU Directive requires a more stringent sound control at the workplaces of musicians. With the aid of a novel constructional conditioning of the rooms for rehearsing, performing, teaching and exercising of music as well as of organisational measures the exposition levels between 85 and 95 dB(A) prevailing here may be reduced by 5 to 10 dB(A). Thus the obligation of wearing ear plugs can be avoided which is inadequate here.

Vol. 4 - 2008

Physiological responses of heart rate and blood pressure to order-picking in deep cold

Author: Karsten Kluth, Helmut Strasser

Keywords: Work Physiological Field Study, Severe Cold Exposure, Heart Rate, Blood Pressure, Manual Material Handling

Summary

Storing and manual handling of groceries in cold stores requires human work at a constant temperature of at least -24°C. Depending on the climatic environment and the physical activities demanded, and even with optimal cold-protective clothing, employees can work only for a limited amount of time in the extreme cold, followed by warming-up periods in suitable recreation rooms. But there is a lack of ergonomically approved human-compatible work-rest-schemes. Therefore, the physiological responses of heart rate and blood pressure were analyzed in a field study carried out in an industrial cold-storage depot. The results show strong inter-individual variations for both the reference level of the physiological parameters and for the work-related and cold-exposure-related responses.

Practical Relevance

Recommendations for tolerability of different cold exposures and the design of cold-protective clothing which, at present, can be found in standards, rules and regulations, as well as in the requirements of the Occupational Health and Safety Act, seem to be useful and very exact. Additionally, there is a controversial discussion about these recommendations and standards in the scientific literature because present knowledge about the impact of such limiting zones on stress and strain in occupational medicine and ergonomics is not secured. This deficiency needs to be ameliorated, primarily in order to create preventive occupational health and safety and, ultimately, also to increase the efficiency of the work process.

Physiological Responses of Core and Skin Temperature to Groceries Handling in Cold-Storage Depots and Sensations of Cold

Author: Helmut Strasser, Karsten Kluth

Keywords: Severe Cold Exposure, Groceries Handling, Core and Skin Temperature, Cold Sensations

Summary

Deep-cold-storage depot commissioners nowadays are continuously exposed to temperatures of -24°C or lower for up to 90 min. After a warming-up phase, exposures to such extreme conditions can be repeated several times a day. The average core temperature – which was taken at the eardrum via a tympanum thermometer – of 35.8°C after the cold exposure was only slightly lower than the maximum value of 36.7°C measured initially. Similar results were found when the temperature at the sole of the foot was measured (decreases of only 2 K to 5.7 K during the cold exposure). However, a substantial number of deep-cold-storage depot commissioners indicated “rather strong“ cold sensations on feet and toes after 90 min. The by and large well-designed protective gear in conjunction with physical work and warming-up phases apparently resulted in physical strain due to the cold that could be compensated almost entirely.

Practical Relevance

Occupational safety and health always has to be secured via investigations into the effects of workload on the employees. Physiological responses of the core and skin temperature to extreme cold exposures which have been recorded in on-the-job measurements during several shifts represent a central part of measures which have to be taken in order to prove endurability of the working conditions. With this respect, also subjectively experienced sensations of cold in various body parts are an indispensible part of a multi-dimensional recording of stress and strain.

Manual restrictions caused by cold exposure of the hands

Author: Karl Jochen Glitz, Uwe Seibel, Ulrich Rohde, Alexander Sievert, Daniel Ridder, Dieter Leyk

Keywords: cold exposure, hands, manual restrictions, manual coordination, hand-grip strength

Summary

In the cold, restrictions of manual dexterity are described below a local hand skin temperature of 15 °C without mentioning the detailed location of the point of measurement. Adequate hand skin temperature can be maintained by gloves or by high metabolic rates. Gloves, however, may restrict manual dexterity. Therefore, cold acclimated personnel performing jobs with high metabolic rates frequently remove their gloves for short periods to execute delicate manual tasks in order to compensate for perceived or actual encumbrance. Estimating the practicability of jobs with low metabolic rates in the cold, restrictions of sufficient manual dexterity and reduced thermal comfort have to be expected when gloves are removed. But are manual dexterity or coordination and hand-grip strength really affected by cold exposure while clothes with proper thermal insulation are worn?

Sixteen cold acclimated volunteers (male; 22.2±4.8 yr; 177.9±6.4 cm; 74.5±8.5 kg; BMI: 23.5±1.9 kg·m^-2; fat: 19.2±3.7 %; clothes: ca. 2 clo) were exposed to cold in a climatic chamber (-5 °C, v_air<1 m·s^-1) for one hour. Prior to cold exposure, baseline measurements of all tests were obtained under room temperature and served as controls. Tympanic membrane temperature was taken before and after cold exposure. Heart rate, mean body skin temperature and hand skin temperatures (dominant hand: little finger; non dominant hand: back of hand, thumb, middle finger and little finger) were measured continuously. Self-perceived thermal sensations ratings of the body and the hands (comfortable “0” - “6” icy) were ascertained. The study included two different conditions: bare hands (U) or gloves (H). Most of the time volunteers remained in standing position with low physical activity. A manual dexterity test (screw/bolt skill test) was conducted after minute 26. Gloves were removed after minute 43 and under both conditions the effects on manual coordination were assessed by means of a hand-steadiness device. Finally, maximal isometric hand-grip force of both hands was recorded over 15 s using a handheld hand-grip ergometer.

Mean heart rates (±SD) were similar: 84±9 min^-1 with U and 85±8 min^-1 with H (p>0.05). Neither core nor mean body skin temperatures showed statistical differences between the two conditions: With variant U, tympanic membrane temperature (±SD) decreased from 37.0±0.5 °C to 35.9±0.6 °C (p<0.001) and with variant H from 36.7±0.4 °C to 35.9±0.7 °C (p<0.001). Mean body skin temperature (±SD) fell from 33.8±0.4 °C to 32.3±0.6 °C (U, p<0.001) and from 33.8±0.7 °C to 32.4±0.9 °C (H, p<0.001). Skin temperature of the little finger from the dominant hand fell below the 15 °C limit in minute 8 with variant U and in minute 43 with the variant H. After removing the gloves (H), the temperature rapidly decreased below 10 °C and reached the level of variant U. In the end the temperatures (±SD) were 7.3±1.8 °C (U) and 7.3±2.0 °C (H). Self-perceived thermal sensation of the body steadily remained at a comfortable level under both conditions: For variant U (±SD) mean scores of 0.1±0.2 at the beginning and 0.5±0.7 in the end of cold exposure were recorded. With variant H the ratings were 0.1±0.2 at the beginning and 0.6±0.8 in the end. Self-perceived thermal sensation of the hands demonstrated the influence of the cold: With variant U (±SD) it was 0.4±0.6 at the beginning and increased to 4.1±0.9 (p<0.001) in the end of cold exposure. With variant H the rating changed from 0.2±0.4 to 3.2±1.0 (p<0.001).

In the screw/bolt skill test performance time (±SD) with bare hands (U) was 123±26 s in the control and 134±25 s in the cold (p>0.05). Compared to gloves (H) there was a statistically significant decrement (p<0.001): Time to completion was 187±64 s in the control and 220±52 s in the cold (p<0.01). In spite of the low hand skin temperatures, differences (±SD) in the hand-steadiness test between controls (14.6±11.7 contacts) and cold (U: 25.4±25.5 contacts; H: 24.4±26.0 contacts) were negligible and no statistical differences could be found. Even maximal isometric hand-grip force showed minor differences. For example: hand-grip force of dominant hand was 500±83 N (±SD) in the controls and remained at this level with 500±79 N (U) and 526±83 N (H) in the end of cold exposure.

In this study the thermal insulation restricted a distinct decrease of core or mean body skin temperature and was sufficient to maintain the thermal comfort of the body. But the low metabolic rates – illustrated-by low heart rates – were insufficient to keep the hands warm. Even with gloves the skin temperature of the little finger reached the 15 °C limit and the remaining benefit of the thermal insulation was rapidly lost when gloves were removed. But in spite of decreasing hand skin temperatures and increasing thermal discomfort of the hands, the effects of cold on manual dexterity or coordination and hand-grip strength were negligible, even when the hand skin temperature dropped below 10 °C.

Therefore, the isolated application of a fixed 15 °C limit for the local skin temperature of the hands as a predictor for manual dexterity is not convenient. The limit for maintaining sufficient manual dexterity might be lower.

Practical Relevance

To estimate the practicability of work with low metabolic rates in the cold it is necessary to maintain core and mean body skin temperature. Cold acclimated personnel may be able to remove gloves for short periods in order to compensate for perceived or actual encumbrance while performing delicate manual tasks. A thin “contact” glove can enlarge the “safety zone” in case of touching cold metal.

A general permit for cold exposure is impossible, due to the multitude of factors in everyday industrial work, such as exposure time, wind, wetness etc.. To prevent cold injury an easy rule should be considered: Only a warm body should be cold exposed!

Heat transfer through protective clothing under symmetric and asymmetric long wave thermal radiation

Author: Peter Bröde, Kalev Kuklane, Victor Candas, Emiel den Hartog, Barbara Griefahn, Ingvar Holmér, Harriet Meinander, Wolfgang Nocker, Mark Richards, George Havenith

Keywords: Heat stress, protective clothing, thermal radiation, skin temperature, heat budget models, thermal manikin

Summary

This report considers results of an EU funded research on thermal properties of protective clothing and their use in the assessment of the thermal strain at work. In order to study the effects of the asymmetry of long wave thermal radiation on the heat transfer through protective clothing, the heat loss under all-side and unilaterally applied radiation with the same incident radiant power of 279 W/m² was measured with a thermal manikin and compared to a reference condition where mean radiant temperature was equal to air temperature. With exposure to radiation a lowered heat loss, i.e. heat gain for the whole covered body area was observed, which did not depend on radiant asymmetry for the dry as well as for the combined dry and evaporative heat loss, and which was attenuated when wearing a more insulating underwear. However, under one-sided radiation a more inhomogeneous spatial distribution occurred with higher heat gains and higher surface temperatures at the irradiated body parts.

Practical Relevance

The direction of thermal radiation in the horizontal plane may be neglected when assessing the physiological heat strain in protective clothing by heat budget models. In contrast to this, it may be advisable to consider radiant asymmetries with respect to thermal comfort with low intensity radiation, and the most intense radiant source when assessing the risk of skin burns.

The Physiological Strain Index (PSI) during acclimation to hot climates

Author: Martin Schütte, Peter Bröde, Bernhard Kampmann, Barbara Griefahn

Keywords: Acclimation, core-temperature, heart rate, PSI

Summary

Acclimation as an adaptive response of the human body to repeatedly occurring heat stress causes a reduction of core temperature (T_co) and heart rate (HR) at the end of heat exposure. Recently, the lowering of T_co and HR was shown to occur already in the resting period preceding heat stress. In addition the so-called Physiological Strain Index (PSI) summarizes both HR and T_co for assessing simultaneously the cardiovascular and thermoregulatory heat stress response. The objective of the present re-analysis of a laboratory study was to examine the suitability of the PSI for describing the attenuation of physiological strain during acclimation, especially when taking into account the lowered resting values of T_co and HR.

The results demonstrated that the PSI indicates a reduced strain following heat acclimation. But since the initial values are also allowed to change during the acclimation process when calculating the PSI, the benefit of acclimation appears to be less pronounced.

All in all the PSI is an easily and quickly calculated index for comparing the physiological strain under different working conditions in hot environments. But its conception seems to be too simple to reproduce the impact of acclimation especially on the lowering of resting HR and T_co. The consideration of such effects requires more complex thermoregulatory models.

Practical Relevance

The present study provide indication of the application area of the PSI (Physiological Strain Index), which was developed for the evaluation of heat strain. The results show that the PSI does not adequately reflect the occurring strain related changes during acclimation particularly the reduction of the resting values of heart rate and core temperature.

Analysis of intra-individual variability of strain during uncompensable heat stress from a longitudinal study

Author: Bernhard Kampmann, Georg Bresser

Keywords: intra-individual variability, heart rate, body temperature, heat stress

Summary

Four mine rescue brigadesmen performed three different standardized trainings in uncompensable heat stress with different equipment, clothing and climatic stress. The subjects performed a standard mine rescue training in a training gallery, lasting for 120 minutes wearing a self contained breathing apparatus (climate: dry bulb temperature 30°C and wet bulb temperature 21°C. On other days a Heat Tolerance Test according to STOKLOSSA was performed in a climatic chamber: 30 minutes walking on a treadmill at an external load of 70 W at 3.5 km/; air temperature 39°C and relative humidity 88 %; clothing: t-shirt, shorts, socks and safety boots. After a further resting period of 1.5 hours a heat exposure in flame protective equipment (FP) was performed (air temperature 32°C wet bulb temperature 27°C; mainly work on a treadmill) in the climatic chamber lasting for a maximum of 90 minutes. The exposure was stopped at request of the subjects or at t_re > 38.5°C or HR > “220-age”, whatever occurred first. Physical and climatic stress of these trainings are typical for training and missions of mine rescue brigadesmen, firemen and other hard work performed in protective clothing.

Heart rates and body temperatures were recorded throughout the exposures. During ten years the diverse trainings were repeated. A significant linear increase over time only was found for body mass in three of the subjects. Specific physical fitness (fitness per body mass) as well as heart rates or body temperatures for initial or final values during the different training procedures showed no significant trend over time.

The intra-individual variability of physiological strain is described in good approximation by normal distributions. The origins of variability were estimated by means of an ANOVA, allowing to estimate confidence intervals e.g. for single measurements of strain parameters as well as the calculation of the required number of measurements that have to be carried out in order to achieve a confidence interval of a desired width. This may be of interest if the question arises whether – for a given subject – a strain parameter will be below a threshold value in the average.

The high degree of variability of strain parameters in a single subject – for the given work load and climatic stress that have been kept as constant as possible – might be explained by different extensions of body core and body shell at the beginning of the exposures.

Practical Relevance

During the ten years of the longitudinal study no linear trend of the strain parameters showed up.

Strain at work during uncompensable heat stress, as it may be considered as typical for firemen or mine rescue brigadesmen, shows high variability for heart rates and body temperatures. The results give confidence intervals for these variables that may be used to estimate whether the average strain e.g. is below or above a given threshold value. For confidence intervals of given widths the required number of measurements is calculated; this is of interest if the strain shall be compared e.g. when using different equipments, or when the evaluated physiological strain shall be compared to the results of mathematical modelling with a given accuracy.