Thereby:



obtained before the start of the study. The questionnaire survey enabled the identification of the main socio-demographic characteristics. In this study, thermal stress was evaluated by the PHS ISO 7933 index "Analytical determination and interpretation of heat stress using calculation of the predicted heat strain" [10]. The physical parameters used to calculate this index come from measurements of the environment as well as from the estimation of the equivalent metabolism in accordance with the ISO 8996 "Ergonomics of the thermal environment - Determination of

*Ergonomic Evaluation of Thermal Stress in a Tunisian Steel Industry*

*DOI: http://dx.doi.org/10.5772/intechopen.98697*

The ISO 7933 standard provides a main advantage of the PHS model related to the reorganization of work, by interposing of short periods of rest during work and the distribution of drinks so as to compensate the water losses taking into account the interindividual differences in physiological responses to heat [1]. This model has been validated using data from 672 laboratory experiments and 237 field experi-

Thermal comfort is defined as a state of satisfaction against a person's thermal environment evaluated by six primary parameters providing this comfort [1]. This comfort was estimated by the PMV and PPD indices described by the ISO 7730 standard [8]. The results of this study were convincing, more than a half (65

It should be noted that the thermal stress is also estimated using the WBGT index described by the ISO 7243 standard [9]. This index has a fairly limited field of application, in particular while evaluating thermal stress during very short periods or conditions close to the thermal comfort [1]. The PHS model seems to be more discriminating than the WBGT index in defining the severity of thermal stress during work situation and organizing work in order to minimize or eliminate thermal stress. Metabolism value estimated for the calculation of this index comes from the results of the recording of the heart rate which gives it an accuracy of the order of 10% and then an accurate estimation [14]. Therefore, only results of the

The climatic conditions category was 3 in 68.18% of subjects (Long-term constraint: discomfort and risk of dehydration after several hours of exposure) and 4 (Short-term constraint: health risk after 30 to 120 minutes of exposure) in 30.3% of workers. The use of this index enabled the assessment of the thermal stress and the management of work in heat [15]. Thus, workers were advised to drink water at 10° C after an average working time of 19.4 5.49 min. A possible alternative is to let employees spontaneously choose their space of work or to allow them to stop

In this study population, the core temperature could reach 38°C after an average working time of 131.3 60.89 min. The World Health Organization (WHO) Technical Report No. 412 published in 1969 stated that: "*It is not recommended that the core body temperature exceeds 38°C for prolonged daily exposure to heavy work*..." [4]. It should be emphasized that, at a rectal temperature of 38°C, an employee does not run any health risk. This limit value concerns the "average" subject and is intended to protect employees who, due to a greater intolerance to heat, evolve to

In this study, more than half of workers (58.75%) know nothing about the risks associated with working in the heat, while 10 employees have already had accidents due to heat (cramps, faintness, stroke. heat). Employees should be informed and trained to recognize signs of thermal stress and prevent the occurrence of these

This study has limitations that warrant mentioning. The thermal stress evaluation was made by physical objective measurements that did not take into account operators' differences. Moreover, the investigation was limited to one company located in the central-eastern region of Tunisia. Therefore, findings cannot be

operators) were not in a situation of thermal comfort.

PSH evaluation will be discussed in this work.

working as soon as they feel some symptoms of strain [1, 16].

higher temperatures, under the same conditions [1].

energy metabolism".

ments [1, 11–13].

accidents [1, 17].

**73**

### **Table 2.**

*Physical parameters of thermal stress.*


#### **Table 3.**

*Thermal stress evaluation.*

In addition, the mean sweat flow was 699.4 160.02 g/h and the mean total water loss was estimated to be 6083.7 1737.29 g.

In accordance with the recommendations of ISO 7933 "Analytical determination and interpretation of thermal stress based on the calculation of the foreseeable thermal strain", it would be imperative to offer all workers oral rehydration by water at 10°C after a calculated average working time of 19.4 5.49 min.

According to these estimates, after 8 hours of work, the average core temperature would reach 38.6 1.03°C. Excessive water loss was reported among 80.3% of workers and would be reached after 292.6 74.64 min. The core temperature would be 38°C, based on these evaluations, among 51.5% of workers who received a heart rate recording after 131.3 60.89 min.

In total, on the basis of these results of the estimation of thermal stresses, 68.18% of subjects would be concerned by a category 3 of climatic condition, namely "Long-term stress: discomfort and risk of dehydration after several hours of exposure" and 30. 3% of them by a category 4 of climatic condition equivalent to a "Short-term constraint: risk to health after 30 to 120 minutes of exposure".

#### **4. Discussion**

This study included measurements of the physical parameters of thermal stress followed by an evaluation of thermal stress. Informed consent from workers was

#### *Ergonomic Evaluation of Thermal Stress in a Tunisian Steel Industry DOI: http://dx.doi.org/10.5772/intechopen.98697*

obtained before the start of the study. The questionnaire survey enabled the identification of the main socio-demographic characteristics. In this study, thermal stress was evaluated by the PHS ISO 7933 index "Analytical determination and interpretation of heat stress using calculation of the predicted heat strain" [10]. The physical parameters used to calculate this index come from measurements of the environment as well as from the estimation of the equivalent metabolism in accordance with the ISO 8996 "Ergonomics of the thermal environment - Determination of energy metabolism".

The ISO 7933 standard provides a main advantage of the PHS model related to the reorganization of work, by interposing of short periods of rest during work and the distribution of drinks so as to compensate the water losses taking into account the interindividual differences in physiological responses to heat [1]. This model has been validated using data from 672 laboratory experiments and 237 field experiments [1, 11–13].

Thermal comfort is defined as a state of satisfaction against a person's thermal environment evaluated by six primary parameters providing this comfort [1]. This comfort was estimated by the PMV and PPD indices described by the ISO 7730 standard [8]. The results of this study were convincing, more than a half (65 operators) were not in a situation of thermal comfort.

It should be noted that the thermal stress is also estimated using the WBGT index described by the ISO 7243 standard [9]. This index has a fairly limited field of application, in particular while evaluating thermal stress during very short periods or conditions close to the thermal comfort [1]. The PHS model seems to be more discriminating than the WBGT index in defining the severity of thermal stress during work situation and organizing work in order to minimize or eliminate thermal stress. Metabolism value estimated for the calculation of this index comes from the results of the recording of the heart rate which gives it an accuracy of the order of 10% and then an accurate estimation [14]. Therefore, only results of the PSH evaluation will be discussed in this work.

The climatic conditions category was 3 in 68.18% of subjects (Long-term constraint: discomfort and risk of dehydration after several hours of exposure) and 4 (Short-term constraint: health risk after 30 to 120 minutes of exposure) in 30.3% of workers. The use of this index enabled the assessment of the thermal stress and the management of work in heat [15]. Thus, workers were advised to drink water at 10° C after an average working time of 19.4 5.49 min. A possible alternative is to let employees spontaneously choose their space of work or to allow them to stop working as soon as they feel some symptoms of strain [1, 16].

In this study population, the core temperature could reach 38°C after an average working time of 131.3 60.89 min. The World Health Organization (WHO) Technical Report No. 412 published in 1969 stated that: "*It is not recommended that the core body temperature exceeds 38°C for prolonged daily exposure to heavy work*..." [4]. It should be emphasized that, at a rectal temperature of 38°C, an employee does not run any health risk. This limit value concerns the "average" subject and is intended to protect employees who, due to a greater intolerance to heat, evolve to higher temperatures, under the same conditions [1].

In this study, more than half of workers (58.75%) know nothing about the risks associated with working in the heat, while 10 employees have already had accidents due to heat (cramps, faintness, stroke. heat). Employees should be informed and trained to recognize signs of thermal stress and prevent the occurrence of these accidents [1, 17].

This study has limitations that warrant mentioning. The thermal stress evaluation was made by physical objective measurements that did not take into account operators' differences. Moreover, the investigation was limited to one company located in the central-eastern region of Tunisia. Therefore, findings cannot be

In addition, the mean sweat flow was 699.4 160.02 g/h and the mean total

**Mean air temperature (Ta) (°C)** 29,66 2,57 27,99 1,87 **Mean air speed (Va) (m/s)** 0,58 0,82 0,23 0,26 **Mean relative humidity (RH) (%)** 59,56 10,98 68, 56 7,78 **Mean Globe temperature (Tg) (°C)** 34, 15 2,87 40,21 7,95

**PMV** 1,5 4,7 3,2 0,47 **PPD (%)** 50 100 97,3 3,7 **WBGT (°C)** 20 29,9 27,5 2,62 **Limit WBGT (°C)** 26,5 30,2 28,4 0,81

**Sweat loss (g/h)** 230 1130 699,4 160,03 **Total water loss (g)** 1780 10600 6083,7 1737,3

**Central temperature after 8 hours of work (°C)** 37,3 42 38,6 1,03 **Time to reach excessive water loss (min)** 160 480 292,6 74,64

and interpretation of thermal stress based on the calculation of the foreseeable thermal strain", it would be imperative to offer all workers oral rehydration by water at 10°C after a calculated average working time of 19.4 5.49 min.

In accordance with the recommendations of ISO 7933 "Analytical determination

**In door Out door**

**Minimum Maximum Mean Standard**

3 60 48 13,19

10 55 19,4 5,49

46 385 131,3 60,89

**deviation**

According to these estimates, after 8 hours of work, the average core temperature would reach 38.6 1.03°C. Excessive water loss was reported among 80.3% of workers and would be reached after 292.6 74.64 min. The core temperature would be 38°C, based on these evaluations, among 51.5% of workers who received a

In total, on the basis of these results of the estimation of thermal stresses, 68.18%

This study included measurements of the physical parameters of thermal stress followed by an evaluation of thermal stress. Informed consent from workers was

of subjects would be concerned by a category 3 of climatic condition, namely "Long-term stress: discomfort and risk of dehydration after several hours of exposure" and 30. 3% of them by a category 4 of climatic condition equivalent to a "Short-term constraint: risk to health after 30 to 120 minutes of exposure".

water loss was estimated to be 6083.7 1737.29 g.

**Time interval Indicated to drink 200 cc of water**

**The central temperature reaches 38°C at the end**

heart rate recording after 131.3 60.89 min.

**4. Discussion**

**72**

**Table 2.**

*Physical parameters of thermal stress.*

*Occupational Wellbeing*

**Work limit time/60 min**

**(min)**

**at 10 °C (min)**

**of (min)**

*Thermal stress evaluation.*

**Table 3.**

extended to all of Tunisian companies, especially with the huge differences in weather, in characteristics and resources between sectors of activity, between industrial process and between operators.

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*DOI: http://dx.doi.org/10.5772/intechopen.98697*

*Ergonomic Evaluation of Thermal Stress in a Tunisian Steel Industry*

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