Globe Temperature and Its Measurement: Requirements and Limitations.

This study addresses the measurement of the globe temperature. For this purpose, two globe thermometers with different diameters (50 and 150 mm) and a variety of thermal environmental conditions were considered. The assessments of the response times and of the influences of the globe diameter and the air velocity on the measured globe temperatures are discussed. The results of the response times clearly put in evidence that the values usually stated in the literature can be questioned and that longer measurement periods must be considered. In fact, response times >30 min were obtained in 68% of the tests performed. Moreover, differences >20ºC were obtained between the 150 and 50 mm sensors, highlighting the influence of the globe diameter. The analysis of the effect of the air velocity on the globe temperature shows mean relative differences >30% between tests in still air and with the higher air velocity considered (1.81 m s-1). On the basis of measurements carried out with the 50 mm globe, correction equations to the standard globe temperature for both natural and forced convection are proposed.

Assessment of thermal environments: working conditions in the portuguese glass industry.

The objective of the present contribution is to assess the exposure to hot thermal environments in the Portuguese glass industry. For this purpose a field survey was carried out and the measurements took place in industrial units - five industries and nineteen workplaces were considered-so all the results are based on real working conditions. In order to assess the level of heat exposure the Wet Bulb Globe Temperature (WBGT) index and the Predicted Heat Strain (PHS) model, defined in ISO Standards 7243 (1989) and 7933 (2004), respectively, were used. According to the WBGT index, the results show that almost 80% of the workplaces under analysis are prone to heat stress conditions. If the PHS model is considered, the results highlight that the predicted and the maximum sweat rates present equal values in about 40% of the workplaces. In addition, in almost 25% of the workplaces the estimated rectal temperature was higher than 38°C, just for an exposure period of one hour. Thus, the present study brings to light the characteristics of the glass industry in terms of the occupational exposure to hot environments and places this activity sector as one of the most difficult to deal with.

Assessment of thermal environments: Working conditions in the Portuguese ceramic industry in 1994 and 2012.

BACKGROUND: The assessment of heat stress in the ceramic industry is a matter of great concern for safety and health of workers. For this purpose working conditions in the last two decades are analysed. OBJECTIVE: To study occupational hot thermal environments in the Portuguese ceramic activity sector in 8 industrial units and 21 workplaces. METHODS: In order to characterise the level of heat exposure, the method proposed by ISO 7243 (1989) based on the Wet-Bulb Globe Temperature (WBGT) index was adopted. RESULTS: Two field surveys, one carried out in 1994 and the other in 2012 are considered. The WBGT mean values varied between 23.7 and 37.8°C in the 1994 survey while in 2012 those values ranged from 21.5 to 30.5°C. In the 1994 evaluations 5 out of 8 (62.5%) of the workplaces present heat stress conditions whereas in the 2012 assessments the corresponding value is 46.2% (6 out of 13 workplaces). CONCLUSIONS: Despite two decades between the two surveys, the results highlight that the overall thermal conditions of the workplaces in the ceramic sector are still quite similar, suggesting that the working conditions have not changed enough, a conclusion that asks for further analysis and improvements.

Evaluation of occupational cold environments: field measurements and subjective analysis.

The present work is dedicated to the study of occupational cold environments in food distribution industrial units. Field measurements and a subjective assessment based on an individual questionnaire were considered. The survey was carried out in 5 Portuguese companies. The field measurements include 26 workplaces, while a sample of 160 responses was considered for the subjective assessment. In order to characterize the level of cold exposure, the Required Clothing Insulation Index (IREQ) was adopted. The IREQ index highlights that in the majority of the workplaces the clothing ensembles worn are inadequate, namely in the freezing chambers where the protection provided by clothing is always insufficient. The questionnaires results show that the food distribution sector is characterized by a female population (70.6%), by a young work force (60.7% are less than 35 yr old) and by a population with a medium-length professional career (80.1% in this occupation for less than 10 yr). The incidence of health effects which is higher among women, the distribution of protective clothing (50.0% of the workers indicate one garment) and the significant percentage of workers (>75%) that has more difficulties in performing the activity during the winter represent other important results of the present study.

Subjective analysis of cold thermal environments.

The present work is dedicated to the study of cold thermal environments in food distribution industrial units through a subjective assessment based on an individual questionnaire which aims to describe the working conditions of employees often exposed to cold. The survey was carried out in Portugal and the sample consists of 1575 valid responses obtained in 61 industrial units. The results show that the food distribution activity sector is characterized by a female population (78.1%) and by a young work force (63.4% of the workers are less than 35 years old). Despite the availability of cold protective clothing (52.8% of the workers indicate one garment) its characteristics require improvements. In addition almost 1/3 of the respondents consider the thermal environment cold and 79.6% of the workers report that working in the cold is harder in wintertime. The results also highlight that 37.3% of the workers report having health problems.

Convective heat transfer from a nude body under calm conditions: assessment of the effects of walking with a thermal manikin.

The present experimental work is dedicated to the analysis of the effect of walking on the thermal insulation of the air layer (I (a)) and on the convective heat transfer coefficients (h (conv)) of the human body. Beyond the standing static posture, three step rates were considered: 20, 30 and 45 steps/min. This corresponds to walking speeds of approximately 0.23, 0.34 and 0.51 m/s, respectively. The experiments took place in a climate chamber with an articulated thermal manikin with 16 independent parts. The indoor environment was controlled through the inner wall temperatures since the objective of the tests was restricted to the influence of the walking movements under calm conditions. Five set points were selected: 10, 15, 20, 25 and 30°C, and the operative temperature within the test chamber varied between 11.9 and 29.6°C. The highest and lowest I ( a ) values obtained were equal to 0.87 and 0.71 clo, respectively, and the reduction in insulation due to walking ranged between 9.8 and 11.5%. The convective coefficients (h (conv)) for the whole body and for the different body segments were also determined for each step rate. In the case of the whole body, for the standing static reference posture, the mean value of h (conv) was equal to 3.3 W/m(2)°C and a correlation [Nu = Nu(Gr)] for natural convection is also presented in good agreement with previous results. For the other postures, the values of h (conv) were equal to 3.7, 3.9 and 4.2 W/m(2)°C, respectively for 20, 30 and 45 steps/min.

Dynamic clothing insulation. Measurements with a thermal manikin operating under the thermal comfort regulation mode.

The main objective of the present work is the assessment of the thermal insulation of clothing ensembles, both in static conditions and considering the effect of body movements. The different equations used to calculate the equivalent thermal resistance of the whole body, namely the serial, the global and the parallel methods, are considered and the results are presented and discussed for the basic, the effective and the total clothing insulations. The results show that the dynamic thermal insulation values are always lower than the corresponding static ones. The highest mean relative difference [(static-dynamic)/static] was obtained with the parallel method and the lowest with the serial. For I(cl) the mean relative differences varied from 0.5 to 13.4% with the serial method, from 5.6 to 14.6% with the global and from 7.2 to 17.7% with the parallel method. In addition, the dynamic tests presents the higher mean relative differences between the calculation methods. The results also show that the serial method always presents the higher values and the parallel method the lowest ones. The relative differences between the calculation methods {[(serial-global)/global] and [(parallel-global)/global]} were sometimes significant and associated to the non-uniform distribution of the clothing insulation. In fact, the ensembles with the highest thermal insulation values present the highest differences between the calculation methods.

Physical modelling of globe and natural wet bulb temperatures to predict WBGT heat stress index in outdoor environments.

The present paper describes a physical model that estimates the globe and the natural wet bulb temperatures from the main parameters generally recorded at meteorological weather stations, in order to predict the wet bulb globe temperature (WBGT) heat stress index for outdoor environments. The model is supported by a thermal analysis of the globe and the natural wet bulb temperature sensors. The results of simultaneous measurements of the WBGT and climatological parameters (solar radiation, wind velocity, humidity, etc.) are presented and used to validate the model. The final comparison between calculated and measured values shows a good agreement with the experimental data, with a maximum absolute deviation of 2.8% for the globe temperature and 2.6% for the natural wet bulb temperature and the WBGT index. The model is applied to the design reference year for Coimbra, Portugal, in order to illustrate its preventative capabilities from a practical point of view. The results clearly show that during the summer there is a critical daily period (1200-1600 hours, local standard time) during which people working outdoors should not be allowed to perform their normal activities.

Measurements of clothing insulation with a thermal manikin operating under the thermal comfort regulation mode: comparative analysis of the calculation methods.

The present work is dedicated to a comparative analysis of calculation methods about clothing insulation with a thermal manikin operating under the thermal comfort regulation mode. The serial, global, and parallel calculation methods are considered and the thermal insulation results for garments (30) and ensembles (9) are discussed. The serial and parallel methods presents the higher and lower values, respectively, and the differences were sometimes significant. Considering the results for the effective thermal insulation, the mean values of the relative differences between the serial and global methods were 25.7% for the daily wear garments, 45.2% for the cold protective garments and 38.5% for the ensembles. The corresponding mean values for the global and parallel methods were 8.7, 15.8, and 10.5%, respectively. Since any uneven clothing insulation is to be expected as a source of error, particular care must be required when the calculation methods deal with cold protective clothing.

Occupational exposure to cold thermal environments: a field study in Portugal.

The present work is essentially dedicated to the study of cold thermal environments. The analysis includes 32 industrial units from 6 activity sectors and the measurements were carried out in 101 workplaces. Different environmental conditions were identified and a clear relationship with the different types of workplaces was established. The work environments were thus allocated to three typical exposure categories corresponding to freezing and refrigerating cold stores and free-running or controlled air temperature manufacturing workplaces. In order to characterize the level of cold exposure, the method proposed by ISO/TR 11079, Technical Report, 1st edn, International Organization for Standardization, Geneva (1993) was adopted. The results for each activity sector demonstrate that a significant percentage of workers are repeatedly exposed to extreme conditions with insufficient clothing insulation. A value between 20 and 40% corresponds to the most critical situation, where the selected clothing ensemble does not provide adequate insulation (I (clr) < IREQ (min)). The ideal scenario, represented by I (clr) values between IREQ (min) and IREQ (neutral), shows the lowest percentages with an overall result of only 10%. When all the sectors are considered together, from a total of 3,667 workers, about one-third (1,151) are exposed to the cold. Among the workplaces under analysis, 14 are characterized by a continuous exposure greater than the DLE (neutral). Those who work under such conditions, on average, have a time shift 60 min longer than the calculated DLE value.