Alain Piette

Prediction of the average skin temperature in warm and hot environments

Abstract 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 °C to 38.6 °C. Experimental conditions included air temperatures (Ta) between 20 and 55 °C, mean radiant temperatures (Tr) up to 145 °C, partial vapour pressures (Pa) from 0.2 to 5.3 kPa, air velocities (va) between 0.1 and 2 m/s, and metabolic rates (M) from 102 to 620 W. Rectal temperature (Tre) was included in the models to increase the accuracy of prediction. Separate models were derived for nude (clothing insulation, Icl, ≤0.2 clo, where 1 clo=0.155 m2 · °C · 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 °C and a humidity of less than 50%) and clothed (0.6 ≤ Icl ≤ 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: Tsk=7.19 + 0.064Ta + 0.061Tr + 0.198Pa− 0.348va + 0.616Tre and Tsk=12.17 + 0.020Ta + 0.044Tr + 0.194Pa − 0.253va + 0.0029M + 0.513Tre. For the nude and clothed subjects, 83.3% and 81.8%, respectively, of the predicted skin temperatures were within the range of ±1 °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.

Relation between functional characteristics of the trunk and the occurrence of low back pain. Associated risk factors.

Study Design. A 2‐year prospective study relating a set of subject characteristics (professional and extraprofessional constraints, personal and anthropometric characteristics, and static and dynamic performance of the trunk) and incidence of low back pain in a population of male Belgian steel workers. Objectives. To investigate the relation between occurrence of new cases of low back pain and prior personal, anthropometric, or functional characteristics. Summary of Background Data. Some functional characteristics‐in particular, dynamic parameters of the trunk such as the velocity‐have been shown to be significantly reduced for low back pain in workers in cross‐sectional studies. The question remained as to whether modifications of these parameters preceded the development of low back pain. Methods. The protocol included a questionnaire, a clinical examination, anthropometric measurements, and a set of functional tests on an isoinertial dynamometer. It was carried out twice, after a 1‐year interval, on a sample of 215 workers without any history of low back pain. The reports of low back pain were again investigated 1 year later. Results. The development of low back pain is related to frontal plane imbalance of the trunk, lower body weight, and perception of heavy lifting efforts at the workplace. Individuals performing dynamic tests at higher velocities appear also to be at a greater risk of low back pain. Conclusions. Although workers with a history of low back pain performed dynamic tests at significantly lower velocities, the probability for development of low back pain in the following year is greater for workers performing such tests at greater velocities.

A comprehensive strategy for the assessment of noise exposure and risk of hearing impairment.

A comprehensive strategy is presented for the evaluation of the daily noise exposure level [LEX,d in dB(A)] and the assessment of the risk of hearing impairment. The risk is defined as the probability for a worker with a given exposure history to noise to develop a hearing deficit above a given threshold. It is shown that for a given accuracy to be obtained on the risk prediction, the precision required on the LEX,d is low at levels around 90 dB(A) and increases at higher levels. The strategy uses the concepts of homogeneous group of exposure (HGE) and stationarity interval (S.I.), defined as the period over which the exposure distribution is the same for the members of the HGE. The number of workers to sample, the number of samples to take for each worker and their duration are discussed. A semi-random sampling is recommended, excluding the periods with low noise exposure. Tests are proposed for the homogeneity of the group and the validity of the S.I.. A corrected standard deviation is defined in order to take into account the skewness of the distribution of the noise equivalent levels of the samples and formulas are presented to estimate the LEX,d, its standard error and the corresponding risk of hearing impairment.

Technical characteristics of overhead cranes influencing the vibration exposure of the operators.

The study was undertaken to determine the technical factors responsible for the generation of vibration and shocks in overhead cranes and therefore responsible for complaints by the workers. Vibration measurements were made on the floor and on the seat of the cabin on 21 cranes. Vibration levels were correlated with the characteristics of the cranes. The study showed that vibration accelerations increased with the span of the crane and were very dependent upon the state of the runway. The type of speed regulation and the position of the cabin also play a significant role. The suspension systems of the cabin and the seat are clearly inadequate to give significant reduction of the vibration. In several cases, it was even shown to amplify the vibration in the most critical frequency range. These results should be taken into account by designers as well as maintenance services in order to prevent the development of vibration at the source.

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.

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.