Occupational heat stress assessment by the Predicted Heat Strain model.

The work of the main European research teams in the field of thermal factors was coordinated in order to improve significantly the Required Sweat Rate model published as an international standard. Many significant modifications were brought, in particular concerning the effects of forced convection, body movements and exercise and the prediction of the skin temperature as a function of the rectal temperature and in case of severe conditions of radiation, humidity and clothing. The criteria for acceptable work durations in hot environments were updated concerning the maximum increase in core temperature and the acceptable water loss. The revised model, called Predicted Heat Strain model, was validated through a set of lab and field experiments involving stable and fluctuating conditions with high and low radiation, humidity and air velocity. It is meanwhile adopted as an ISO and CEN standard. In addition, a strategy was developed to assess the risks of heat disorders in any working situation. It is based on the three highest stages of the SOBANE strategy: an "Observation" method for improving simply the thermal conditions of work; an "Analysis" method to evaluate the magnitude of the problem and optimise the choice of solutions and an "Expert" method for in depth analysis of the working situation when needed.

Temperature limit values for touching cold surfaces with the fingertip.

OBJECTIVES: At the request of the European Commission and in the framework of the European Machinery Directive, research was performed in five different laboratories to develop specifications for surface temperature limit values for the short-term accidental touching of the fingertip with cold surfaces. METHODS: Data were collected in four laboratories with a total of 20 males and 20 females performing a grand total of 1655 exposures. Each touched polished blocks of aluminium, stainless steel, nylon-6 and wood using the distal phalanx of the index finger with a contact force of 1.0, 2.9 and 9.8 N, at surface temperatures from +2 to -40 degrees C for a maximum duration of 120 s. Conditions were selected in order to elicit varying rates of skin cooling upon contact. Contact temperature (TC) of the fingertip was measured over time using a T-type thermocouple. RESULTS: A database obtained from the experiments was collated and analysed to characterize fingertip contact cooling across a range of materials and surface temperatures. The database was subsequently used to develop a predictive model to describe the contact duration required for skin contact temperature to reach the physiological criteria of onset of pain (15 degrees C), onset of numbness (7 degrees C) and onset of frostbite risk (0 degrees C). CONCLUSIONS: The data reflect the strong link between the risk of skin damage and the thermal properties of the material touched. For aluminium and steel, skin temperatures of 0 degrees C occurs within 2-6 s at surface temperatures of -15 degrees C. For non-metallic surfaces, onset of numbness occurs within 15-65 s of contact at -35 degrees C and onset of cold pain occurs within 5 s of contact at -20 degrees C. The predictive model subsequently developed was a non-linear exponential expression also reflecting the effects of material thermal properties and initial temperature. This model provides information for the protection of workers against the risk of cold injury by establishing the temperature limits of cold touchable surfaces for a broad range of materials, and it is now proposed as guidance values in a new international standard.

The SOBANE strategy for the management of risk, as applied to whole-body or hand-arm vibration.

OBJECTIVE: The objective was to develop a coherent set of methods to be used effectively in industry to prevent and manage the risks associated with exposure to vibration, by coordinating the progressive intervention of the workers, their management, the occupational health and safety (OHS) professionals and the experts. The methods were developed separately for the exposure to whole-body and hand-arm vibration. RESULTS: The SOBANE strategy of risk prevention includes four levels of intervention: level 1, Screening; level 2, Observation; level 3, Analysis and; level 4, Expertise. The methods making it possible to apply this strategy were developed for 14 types of risk factors. The article presents the methods specific to the prevention of the risks associated with the exposure to vibration. CONCLUSIONS: The strategy is similar to those published for the risks associated with exposure to noise, heat and musculoskeletal disorders. It explicitly recognizes the qualifications of the workers and their management with regard to the work situation and shares the principle that measuring the exposure of the workers is not necessarily the first step in order to improve these situations. It attempts to optimize the recourse to the competences of the OHS professionals and the experts, in order to come more rapidly, effectively and economically to practical control measures.

Participative management strategy for occupational health, safety and well-being risks.

The article discusses the principles that underlie a coherent and efficient prevention program for occupational health, safety and well-being: the need of a global approach of these problems not only at the workplace but for the whole of the living conditions at work; a clear understanding of the complementarity between the different partners of this prevention; the role of actor of the workers and therefore the absolute necessity of a participative approach; the real usefulness of measurements and of risk quantification in general; the differences between risk assessment and risk management and the specificities of small and medium size enterprises. On the basis of these principles, the various steps and levels of intervention are defined. The SOBANE prevention strategy is introduced and its 4 levels (Screening, Observation, Analysis and Expertise) are described as well as the consultation guide Déparis for the Screening level. The strategy proved to make it possible to approach the work situations progressively in small as well as in large companies, to coordinate the cooperation between the workers, the technical staff and the occupational health practitioners and to prevent the problems more rapidly, more efficiently and more economically. The paper describes the role of a 'facilitator' to introduce the philosophy and the tools of the SOBANE strategy in the company, to monitor its application and insure the continuity and the efficiency of the participatory approach.

The SOBANE risk management strategy and the Déparis method for the participatory screening of the risks.

INTRODUCTION: The first section of the document describes a risk-prevention strategy, called SOBANE, in four levels: screening, observation, analysis and expertise. The aim is to make risk prevention faster, more cost effective, and more effective in coordinating the contributions of the workers themselves, their management, the internal and external occupational health (OH) practitioners and the experts. These four levels are: screening, where the risk factors are detected by the workers and their management, and obvious solutions are implemented; observation, where the remaining problems are studied in more detail, one by one, and the reasons and the solutions are discussed in detail; analysis, where, when necessary, an OH practitioner is called upon to carry out appropriate measurements to develop specific solutions; expertise, where, in very sophisticated and rare cases, the assistance of an expert is called upon to solve a particular problem. METHOD: The method for the participatory screening of the risks (in French: Dépistage Participatif des Risques), Déparis, is proposed for the first level screening of the SOBANE strategy. The work situation is systematically reviewed and all the aspects conditioning the easiness, the effectiveness and the satisfaction at work are discussed, in search of practical prevention measures. The points to be studied more in detail at level 2, observation, are identified. The method is carried out during a meeting of key workers and technical staff. CONCLUSION: The method proves to be simple, sparing in time and means and playing a significant role in the development of a dynamic plan of risk management and of a culture of dialogue in the company.

Co-ordinated strategy of prevention and control of the biomechanical factors associated with the risk of musculoskeletal disorders.

OBJECTIVES: To propose a cost-effective set of methods (strategy) to improve biomechanical working conditions and prevent the development of musculoskeletal disorders. METHODS: The strategy was developed according to the philosophy already used for other aspects of working conditions. It was then tested in ten industrial situations with various characteristics, to check its understanding, its usability, and its efficiency. RESULTS: The strategy includes a five-page leaflet ( screening) aimed at motivating the operators to check the problems and bring about immediate solutions if possible. A stage-2 observation checklist is then proposed to guide the discussions during a meeting of the protagonists (workers and management). The assistance of an occupational health practitioner might become indispensable at stage 3 to deepen the analysis of the remaining problems, while experts are requested only in exceptional cases (stage 4, expertise). This strategy was positively judged by the users and proved to be effective in motivating and co-ordinating the protagonists. CONCLUSION: The strategy proved to consider effectively all biomechanical aspects that might contribute to the development of musculoskeletal disorders (MSDs). It proved also to be participatory, placing the operators and their management at the centre of the intervention as the main actors, and organising when to turn to an occupational health practitioner or an expert for assistance.

Temperature limit values for gripping cold surfaces.

OBJECTIVES: At the request of the European Commission and in the framework of the European Machinery Directive, research was conducted jointly in five different laboratories to develop specifications for surface temperature limit values for the gripping and handling of cold items. METHODS: Four hundred and fourteen experiments were run where male and female subjects were invited to grip for up to 20 min cold bars of different contact coefficients, i.e. polished wood, nylon, stone, steel and aluminium. The air temperature and the bars' initial surface temperatures ranged between 0 and -30 degrees C for the various experiments. While gripping the bars, either only the hand or the whole body was exposed to cold. RESULTS: The data were used to develop a prediction formula and a graph of the surface temperature limit values in order for the skin contact temperature not to reach <15 degrees C. This duration is shown to offer a significant degree of safety with respect to the minimal surface temperature spontaneously tolerated by the subjects. CONCLUSIONS: Experiments and modelling must be pursued to extend these data to other conditions of exposure.

Assessment of the risk of heat disorders encountered during work in hot conditions.

OBJECTIVE: To co-ordinate the work of the main European research teams in the field of thermal factors in order to develop and improve significantly the methods presently available for assessing the risks of heat disorders encountered during work in hot conditions. METHOD: Each item from the required sweat rate model was reviewed on the basis of the most recent literature. A database with 1,113 laboratory and field experiments, covering the whole range of hot working conditions, was assembled and used for the validation. RESULTS: Influence of clothing ensemble on heat exchange: methods and formulas were developed that take into account the dynamic effects associated with forced convection and the pumping effect associated with body movements and exercise. Prediction of the average skin temperature: the model used in the required sweat rate standard ISO 7933 was extended to cover more severe conditions with high radiation and high humidity and different clothing and take into account the rectal temperature for the prediction of the skin temperature. Criteria for estimating acceptable exposure times in hot work environments: criteria were reviewed and updated concerning the maximum increase in core temperature and the acceptable water loss, for acclimatised and nonacclimatised subjects. These limits are intended to protect 95% of the population. Measuring strategy: a strategy was developed to assess the risks in any working situation with varying conditions of climate, metabolic rate or clothing. A detailed methodology was developed in three stages: an "observation" method for the recognition of the conditions that might lead to thermal stress; an "analysis" method for evaluating the problem and optimising the solutions; and an "expert" method for in-depth analysis of the working situation when needed. VALIDATION: the different results were used to prepare a revision of the interpretation procedure proposed in the ISO standard 7933. We validated the modified approaches using the database. This involved the whole range of conditions for which the model was extended, namely conditions with high and low radiation, humidity and air velocity as well as fluctuating conditions. Based on these results, the predicted heat strain model was developed: it is presently proposed as an ISO and CEN standard.

Associations between hand-wrist musculoskeletal and sensorineural complaints and biomechanical and vibration work constraints.

A 3-year prospective epidemiological study was conducted to investigate the relationship between musculoskeletal complaints (MS) and sensorineural complaints (SN) of the workers in the hand-wrist region. A group of 69 workers (G1) using vibrating tools in eight different working situations was compared to a group of 62 workers (G2) performing heavy work without vibration and 46 workers (G3) performing light work without vibration. Biomechanical constraints (force, postures, repetitiveness and movement velocities) were analysed for each working situation and the vibration exposure at the eight workplaces with the 69 workers. MS and SN data were collected using the nordic questionnaire, modified to collect information about the frequency intensity and duration of complaints. The prevalence of complaints at the start of the study was significantly greater for G1 (72.5%) than for G2 (56.5%), itself greater than for G3 (30.4%). The prevalence of SN was about 40% for G1 and 2.5 times smaller in the two other groups. During the two years follow-up, new cases of 'serious' MS and SN developed. The annual incidence was respectively 8.3 and 5.4% on average. The incidence of MS was slightly but not statistically significantly greater for G1, while the incidence of SN was statistically higher (P<0.01) for G1 (10.9%) than for the two other groups (4.1 and 2.1%). Forces and angular repetitiveness were the only biomechanical factors significantly greater for G1. The vibration exposure duration of the G1 workers varied, in average, from 10 to 70% of the work time and the weighted personal exposure amplitude (A(EPw)) varied from 0.5 to 25.4 ms(-2). The probabilities of complaints at the beginning of the study (cross-sectional study) were estimated using multiple logistic regression models. The prevalence odds ratio (POR) for MS was equal to 4 for G1 compared to G2 and equal to 9 compared to G3. Force and vibration exposure were the main constraint parameters associated with this likelihood. As far as the SN are concerned, G2 and G3 were not statistically different, but the POR for the G1 workers was 4.5 compared to both groups. The most significant constraint factor was the weighted personal exposure acceleration. The same procedure was used to estimate the likelihood of development of 'serious' complaints (longitudinal study). The three groups did not appear significantly different concerning the 'serious' MS, while the incidence odds ratio (IOR) of 'serious' SN was very high (28.5) and significantly greater for G1 than for the two other groups. The likelihood of development of 'serious' SN increased with A(EPw). According to this prediction model, the risk of 'serious' SN would be about 6% at the proposed European 'action' value (2.5 ms(-2)) and about 10% at the 'limit' value (5 ms(-2)).

Review of the factors associated with musculoskeletal problems in epidemiological studies.

OBJECTIVES: To review systematically all epidemiological studies of the past 15 years concerning the factors associated with musculoskeletal disorders (MSDs) or complaints of the neck and upper limbs. METHODS: Fifty-seven cross-sectional and seven longitudinal studies were reviewed. A list was made of all personal, occupational, extra-occupational and psycho-organisational factors taken into consideration in each study, and of those that were found in association with MSDs. MSDs of the neck-shoulder region (NSs) and hand-wrist (HWs) were considered separately. About 70 different factors are listed. RESULTS: This inventory identifies the factors or categories of factors that were generally taken into consideration. It makes it possible also to evaluate the strength of the association with a given factor, in considering the number of studies finding an association, and those that did not consider this factor. Based on this review, some factors taken into consideration (such as weight or hobbies) could be excluded in further studies, and replaced by more specific psycho-organisational factors.

Development and validation of the predicted heat strain model.

Eight laboratories participated in a concerted research project on the assessment of hot working conditions. The objectives were, among others, to co-ordinate the work of the main European research teams in the field of thermal factors and to improve the methods available to assess the risks of heat disorders at the workplace, and in particular the "Required Sweat Rate" model as presented in International Standard ISO 7933 Standard (1989). The scientific bases of this standard were thoroughly reviewed and a revised model, called "Predicted Heat Strain" (PHS), was developed. This model was then used to predict the minute by minute sweat rates and rectal temperatures during 909 laboratory and field experiments collected from the partners. The Pearson correlation coefficients between observed and predicted values were equal to 0.76 and 0.66 for laboratory experiments and 0.74 and 0.59 for field experiments, respectively, for the sweat rates and the rectal temperatures. The change in sweat rate with time was predicted more accurately by the PHS model than by the required sweat rate model. This suggests that the PHS model would provide an improved basis upon which to determine allowable exposure times from the predicted heat strain in terms of dehydration and increased core temperature.

Musculoskeletal complaints, functional capacity, personality and psychosocial factors.

OBJECTIVES: The aim of the research was to study the association between psychosocial and personality factors, and neck and wrist-hand musculoskeletal complaints, taking account of the occupational factors of force, posture and repetitiveness, and non-occupational risk factors such as sport, hobbies, medical history. METHODS: During personal interviews 133 women from seven different companies, working at constraining workplaces (very repetitive work), answered several questionnaires. These concerned: personal characteristics and history; work characteristics; psychosocial factors (perception and appreciation of the work situation, satisfaction at work, stress symptoms, Karasek questionnaire) and personality factors (neuroticism, conscientiousness, type-A behavior). They also undertook functional and psychomotor tests (wrist angles, grip strength and a dexterity test). Logistic regression models were calculated. RESULTS: Wrist-hand complaints appear to be associated with some personal characteristics (smoking habits, fewer hobbies), work constraints (fewer breaks, heavy lifting efforts) and some personality (introversion) and psychosocial factors (worse appreciation of work). Neck complaints are also associated with some personal characteristics (young people, small, bad health, hormonal problems, fewer hobbies), some personality (urgency of time) and psychosocial factors (constraints as seen by the supervisor). CONCLUSION: The study confirms the multifactorial character of the musculoskeletal disorders and underlines the need for a global ergonomic approach to work situations, taking into account all their physical, psychological and social components.

Can a battery of functional and sensory tests corrobrate the sensorineural complaints of subjects working with vibrating tools?

OBJECTIVES: The objective of the present paper is to study the relationship between the early sensorineural symptoms, classified according to the Stockholm scale, and the results of the main functional and sensory tests described in the literature, in subjects working with vibrating tools. METHODS: Three groups of male workers were selected from industry: one group (69 subjects) exposed to hand-arm vibration in several workplaces, one group (62) performing heavy and repetitive hand and arm work but without exposure to vibration, and one control group (46) performing light and non-repetitive tasks without vibration. All the workers were interviewed by questionnaire, about their personal characteristics, their health status, their actual and past working conditions and the episodes of tingling at the level of the fingers. From these reported symptoms, the sensorineural stage of the hand-arm vibration was determined using the Stockholm scale. Based on the review of the literature, we selected six functional and sensory tests: maximum voluntary grip force, maximum angles of the wrist, pressure perception threshold test, vibration perception threshold test, distal sensory latency and the Purdue Pegboard test. Each test was performed by the workers in the three groups. RESULTS: No main differences were observed between the personal characteristics of the three groups. According to the Stockholm scale, the sensorineural symptoms were mainly at stage SN1, with 9% at stage SN2 and none at stage SN3. These symptoms are associated with exposure to vibration, and had a prevalence of 40% in group 1, versus 20% in the two other groups. Furthermore, 25% of the workers exposed to vibration complained of symptoms at least once a week, compared with only 2% in the other groups. The multivariate logistic regression analysis showed an association between the existence of symptoms and a decrease in the maximum flexion angle of the wrist and an increase in the pressure perception threshold. This association, however, was too low to determine limit values with a sensitivity and specificity sufficiently high to make a reliable diagnosis. CONCLUSIONS: The sensorineural symptoms at stage N1 on the Stockholm scale, experienced occasionally by some 40% of the users of vibrating tools, could not be corroborated by the functional and sensory tests.

Prediction of the average skin temperature in warm and hot environments.

The prediction of the mean skin temperature used for the Required Sweat Rate index was criticised for not being valid in conditions with high radiation and high humidity. Based on a large database provided by 9 institutes, 1999 data points obtained using steady-state conditions, from 1399 experiments and involving 377 male subjects, were used for the development of a new prediction model. The observed mean skin temperatures ranged from 30.7 degrees C to 38.6 degrees C. Experimental conditions included air temperatures (Ta) between 20 and 55 degrees C, mean radiant temperatures (Tr) up to 145 degrees C, partial vapour pressures (Pa) from 0.2 to 5.3 kPa, air velocities (v(a)) between 0.1 and 2 m/s, and metabolic rates (M) from 102 to 620 W. Rectal temperature (T(re)) was included in the models to increase the accuracy of prediction. Separate models were derived for nude (clothing insulation, I(cl), < or = 0.2 clo, where 1 clo = 0.155 m2 x degrees C x W(-1), which is equivalent to the thermal insulation of clothing necessary to maintain a resting subject in comfort in a normally ventilated room, air movement = 10 cm/s, at a temperature of 21 degrees C and a humidity of less than 50%) and clothed (0.6 < or = I(cl) < or = 1.0 clo) subjects using a multiple linear regression technique with re-sampling (non-parametric bootstrap). The following expressions were obtained for nude and clothed subjects, respectively: T(sk) = 7.19 + 0.064Ta + 0.061Tr + 0.198Pa - 0.348v(a) + 0.616T(re) and T(sk) = 12.17 + 0.020Ta + 0.044Tr + 0.194Pa - 0.253v(a) + 0.0029M + 0.513T(re). For the nude and clothed subjects, 83.3% and 81.8%, respectively, of the predicted skin temperatures were within the range of +/- 1 degree C of the observed skin temperatures. It is concluded that the proposed models for the prediction of the mean skin temperature are valid for a wide range of warm and hot ambient conditions in steady-state conditions, including those of high radiation and high humidity.

Criteria for estimating acceptable exposure times in hot working environments: a review.

OBJECTIVES: To revise the criteria used in the present "Required Sweat Rate" standard ISO 7933 (1989) for the prediction of the maximum duration of work in hot environments. METHODS: Review of the literature and in particular, of the bases for the present criteria. RESULTS: A new method is proposed, to take into account the increase in core temperature associated with activity in neutral environments. The prediction of maximum wetness and maximum sweat rates are revised, as well as the limits for maximum water loss and core temperature. CONCLUSION: An improved set of maximum values and limits is described, to be used in the revised version of the ISO 7933 standard. Due to the major modifications to the "Required Sweat Rate" index and in order to avoid any confusion, it is suggested that the revised model be renamed the "Predicted Heat Strain" (PHS) model.

Strategy for prevention and control of the risks due to noise.

OBJECTIVES: To propose a strategy for progressively controlling the exposure to noise in industry as much as possible. To propose a method that could, in the first stage, be used by the workers and management themselves to control exposures to noise as much as possible, and then, in later stages, when necessary, progressively call in the assistance of specialists and experts to identify more complex solutions and organise personal protection and medical surveillance. METHODS: The strategy includes three stages. Stage 1 is observation, simple and easy to use by the workers to recognise the problems, identify straightforward solutions, and call for assistance when needed. Stage 2 is analysis, more complex but more costly, performed with the assistance of occupational health specialists to identify more technical control measures and set up a programme to conserve hearing. Stage 3 is expertise, performed with the assistance of acoustic experts for special measurements and control measures. CONCLUSIONS: The proposed strategy enriches the assessment procedure that is usually recommended, by providing for one preliminary stage used by the people directly concerned. It explicitly recognises (a) the competence of the workers and management about their working conditions and (b) that knowledge and measurements of acoustics are not an absolute prerequisite for solving-at least partly-noise problems. It attempts to organise in sequence and optimise the cooperation between the workers, the occupational health specialists, and the experts in acoustics.

The effects of wind and human movement on the heat and vapour transfer properties of clothing.

This paper integrates the research presented in the papers in this special issue of Holmér et al. and Havenith et al. [Holmér, I., Nilsson, H., Havenith, G., Parsons, K. C. (1999) Clothing convective heat exchange: proposal for improved prediction in standards and models. Annals of Occupational Hygiene, in press; Havenith, G., Holmér, I., den Hartog, E. and Parsons, K. C. (1999) Clothing evaporative heat resistance: proposal for improved representation in standards and models. Annals of Occupational Hygiene, in press] to provide a practical suggestion for improving existing clothing models so that they can account for the effects of wind and human movement. The proposed method is presented and described in the form of a BASIC computer program. Analytical methods (for example ISO 7933) for the assessment of the thermal strain caused by human exposure to hot environments require a mathematical quantification of the thermal properties of clothing. These effects are usually considered in terms of 'dry' thermal insulation and vapour resistance. This simple 'model' of clothing can account for the insulation properties of clothing which reduce heat loss (or gain) between the body and the environment and, for example, the resistance to the transfer of evaporated sweat from the skin, which is important for cooling the body in a hot environment. When a clothed person is exposed to wind, however, and when the person is active, there is a potentially significant limitation in the simple model of clothing presented above. Heat and mass transfer can take place between the microclimate (within clothing and next to the skin surface) and the external environment. The method described in this paper 'corrects' static values of clothing properties to provide dynamic values that take account of wind and human movement. It therefore allows a more complete representation of the effects of clothing on the heat strain of workers.

Strategy for evaluation and prevention of risk due to work in thermal environments.

A strategy in four successive stages is described and justified for the prevention and control of thermal problems in the workplace. This should allow these problems to be approached and solved progressively in small as well as large companies by relying successively, when necessary, on the complementary competencies of the workers themselves, their technical assistance, the occupational health specialists and the experts. The criteria to fulfil at each stage are described and discussed. Appendix 1 describes in detail the methods to be used at stages 2, "Observation" by the workers and their assistance; at stage 3, "Analysis" with the help of specialists; and outlines the stage 4, "Expertise".

Neurological and functional effects of short-term exposure to hand-arm vibration.

OBJECTIVE: The aim of the present study was to quantify the sensory and functional effects resulting from a short-duration (30 min) exposure to hand-arm vibration. SUBJECTS AND METHODS: Nine subjects went through nine laboratory experiments. For 32 min they grasped a handle vibrating at three different amplitudes (5, 20, and 80 ms-2) and at three frequencies (31.5, 125, and 500 Hz). Additionally, a reference experiment was conducted in which the handle did not vibrate. Three sensory tests [vibration perception threshold (VPT), pressure perception threshold (PPT), and distal sensory latency time (DSL)], two functional tests [Purdue peg-board (PPB) and maximal voluntary force (MVF)], and a questionnaire concerning the perceived paresthesia and numbness were completed before, during, and after exposure. RESULTS: A 32-min period of exposure to vibration leads to a temporary threshold shift (TTS) of the VPT and to the development of paresthesia and numbness. The VPT appears to vary with the exposure duration according to a first-order model with a time constant about equal to 3 min. The TTS increases with the vibration acceleration amplitude and is greater for an exposure frequency of 125 Hz than for that of 31.5 or 500 Hz. It is also greater at the test frequency 125 Hz than at 31.5 Hz. The other tests do not demonstrate any significant variation. In particular, the PPB test does not demonstrate any loss of dexterity. CONCLUSION: After some 30 min of exposure to vibration the VPTs are increased and paresthesia and numbness develop. However, these do not appear to influence significantly the capacity or performance at work.

Temporary threshold shift of the vibration perception threshold following a short duration exposure to vibration.

The objective of this study is to analyze the evolution of the vibration perception threshold (VPT) following a short duration exposure to vibration. The literature reports experiments with 3 to 10 min exposure to vibration after which a steady state is not necessarily reached. The temporary threshold shift (TTS) of the VPT is extrapolated from data recorded during the recovery period. The assumption of a linear decrease with the logarithm of time gives erroneous results for the TTS extrapolated at the end of the exposure. 81 experiments were conducted on 9 young subjects without any neurological problem, exposed to acceleration amplitudes of 5, 20 and 80 ms-2 at frequencies of 31.5 (conditions 1 to 3), 125 (conditions 4 to 6) and 500 Hz (conditions 7 to 9). The exposure to vibration lasted 32 min and was interrupted shortly at time 2, 4, 8, 16 to record the VPT at 31.5 and 125 Hz. The VPT was also recorded before the exposure and several times during the recovery. The evolution of the VPT appears to follow a first order model characterized by a maximum amplitude TTS, a time constant (tau) and a residual value (r, as a fraction of the TTS). The correlation coefficients between observed and predicted values in the 81 experiments are 0.881 at 31.5 Hz and 0.885 at 125 Hz. The TTS is influenced by the exposure amplitude and frequency and is different at the two test frequencies. It varies also significantly between the subjects and with their initial VPT value. The time constant is about 3 minutes at both test frequencies, while the residual fraction is of the order of 0.14 at 31.5 Hz and 0.07 at 125 Hz. Both parameters appear to be independent of the exposure parameters.