**2.2 Thermal stress analysis**

skips past the 30°C (86°F) mark in the middle of the month and rises to 33°C (91°F)

This work aims to assess thermal stress based on the various measurable thermal stress parameters (wet bulb temperature, air speed, radiation temperature, black

This is an exhaustive cross-sectional study carried out during the two months of August and September 2015, in a Tunisian steel company specialized in the manufacture of springs for heavy vehicles and located in the industrial zone of Teboulba-Moknine of the governorate of Monastir, Tunisia. This company counted 120 workers. A list of names and contact details of all workers was provided by the Human Resources Management Department. Included patients were those who had a job tenure exceeding one year and belonged to production workshops. Exclusion criteria consisted of a participation refusal and a disability or cognitive impairment

The survey was preceded by an individual interview with each eligible worker in order to explain the objectives of the work, its practical progress, guarantee anonymity and obtain informed consent. During the survey, data collection focused on general characteristics, as well as thermal stress measurements. Data analysis was subsequently carried out by the same investigator, using statistical and computer

1.General characteristics related to age, weight, height, Body Mass Index

2.Measurement of the thermal environment carried out in the workstation of each worker and in the external environment (rest area during recovery breaks). These recordings were preceded by open observation days to estimate the actual duration of the activity set at five hours. Open observation also enabled a contact with the operators and the collection of their opinions concerning the time and extent of the temperature peak. The thermal stress mainly concerns the morning and afternoon shiftwork and extended from 7 am to 7 pm. Thus, measurements were made every 15 minutes at the workstations. The values obtained were means of all measurements

performed. These measurements were carried out in accordance with the ISO

workstation at a height of 1.5 m, far from the employees and sheltering the sensor against radiation (sun, oven, etc.). It is a calibrated device with a low response time, a stabilization time of a few seconds enabling punctual measurement of air temperature and relative humidity.

• a vane anemometer (YK-80AP Vane Anemometer) for measuring air speed. The measurement was discontinuous and the axis of rotation was

7726 standard "*Ergonomics of the thermal environment - Instruments for*

• a thermo-hygrometer (TA5 Thermal Anemometers) placed at the

*measuring physical quantities*" [4] using:

placed in the direction of the air flow.

in July and August.

*Occupational Wellbeing*

globe temperature...).

**2. Materials and methods**

precluding participation.

programs.

**68**

**2.1 Data collection**

(BMI)...

This evaluation was conducted by the program "Ergonomics of work in heat - Calculation of PMV indices - PPD, WBGT and P.H.S." developed by Prof. Malchaire [5] and based on the various physical parameters of the thermal environment (air temperature, black globe temperature, relative humidity, speed of air) as well as on:

	- Predicted Mean Vote (PMV) at work and during recovery. This PMV index predicts the average vote value of a large group of people on the following seven-point thermal sensation scale: + 3 very hot; + 2 hot; + 1 slightly hot; 0 neither hot nor cold; �1 slightly cold; �2 cold; �3 very cold [1]
	- Predicted Percentage of Dissatisfied (PPD) in the workplace and during recovery. This PPD index is defined as the percentage of people who, placed in identical conditions, consider themselves cold/very cold or hot/very hot. These are the people who would have cast a vote outside the interval (�1, 1) on the sensation scale [1]. To obtain a thermal comfort situation, it is recommended that the PPD be less than 10%, which corresponds to a PMV between �0.5 and + 0.5 [1].
	- Thermal sensation in work situation and during recovery: This index is calculated from the PMV and PPD indices and In accordance with ISO 7730 "Ergonomics of the thermal environments - Analytical determination and interpretation of thermal comfort by calculating the PMV and PPD indices and by local thermal comfort criteria" [8].
	- The natural humid temperature (Thn) in work situation and during recovery.
	- The Wet Bulb Globe Temperature (WBGT) in the workplace and during recovery. The WBGT corresponds to a weighting between the radiation temperature and the natural wet bulb temperature.

$$\begin{aligned} \text{WBGT} &= \text{0.7 then} + \text{0.3 tg without solar R} \\ &= \text{0.7 then} + \text{0.2 tg} + \text{0.1 ta with solar R} \end{aligned} \tag{1}$$

◦ The WBGT limits in work situation and during recovery

The working hours - rest limits (K): This duration is calculated in accordance with ISO 7243 "Hot environments - Estimation of the thermal stress of man at work, based on the WBGT index (wet bulb and black globe temperature)" [9] and according to the following equation:

$$\text{K} = \frac{\text{32} - \text{WBGT}}{\text{32} - \text{WBGT}\_{\text{lim}}} \tag{2}$$

humidity, and air speed) as well as on the equivalent metabolism M and the Iclo clothing insulation index evaluated in accordance with the ISO 9920 standard "Ergonomics of the thermal environment - Determination of thermal insulation and

Men 80

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

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

Mean age (extremes) 37,9 9,25 years (from 21 to 54 years)

Mean job tenure (extremes) 12,5 11,4 years (from1 to 35 years).

62 (77,5%) 18 (12,5%)

61 (76,25%) 10 (12,5%) 27 (33,75%) 24 (30%)

26,9 3,6 kg/m<sup>2</sup> (17,8 à 38,7 kg/m2) 19 (23.75%) 49 (61,25%) 12(15%).

1.*Thermal environment*: The mean air temperature inside the workshops was 29.66 2.57°C with a mean air speed of 0.58 0.82 m/s, a mean relative humidity of 59, 56 10.98 and a mean global temperature of 34.15 2.87°C

2.*Thermal stress evalation*: Based on the evaluation of the equivalent metabolism and the characteristics of the thermal environment, the thermal stress to which

the workers of the different production workshops were exposed, was evaluated by the indices of Predicted Mean Vote (PMV) and Predicted

• Mean PMV of 3.2 0.47 with extremes ranging from 1.5 to 4.7.

• The Thermal sensation was rated "very hot" on 98.75% of all working

• The mean WBGT limit 28.4 0.81°C. Based on previous estimates, and in accordance with ISO 7243 "Hot environments - Estimation of the thermal stress of humans at work, based on the WBGT index (wet bulb and black globe temperature)" [9], the mean cut-off working time was evaluated at

Percentage of Dissatisfied (PPD) as follows (**Table 3**):

• The mean WBGT was 27.5 2.62°C

• Mean PPD 97.3 3.7% with extremes of 50 to 100%.

resistance to evaporation of a clothing" [7].

(**Table 2**).

**Characteristics**

Groups: n(%) • **Men > 45 years:** • **Men < 45 years:**

Depending children: • 0 **child** • 1 **to** 3 **children** • ≥3 **children**

Mean BMI (extremes)

Married

• **Normal** • **Overweight** • **Obesity**

**Table 1.** *Study population.*

Thereby:

days.

**71**

48 13.19 min.

	- a. C1: Comfort category: neither discomfort nor health risk;
	- b. C2: Discomfort category: discomfort that can be very significant, but without health risk;
	- c. C3: Category of long-term constraint: discomfort and risk of dehydration after several hours of exposure;
	- d. C4: Short-term stress category: health risk after 30 to 120 minutes of exposure;
	- e. C5: Immediate Constraint Category: health risk even for very short exposure (less than 30 minutes)

#### **3. Results**

#### **3.1 Study population**

The survey was carried out exhaustively among the operators of the production workshops of the steel company, and included a total of 80 male workers. The mean age was 37.9 � 9.25 years and the mean professional tenure was 12.5 � 11.4 years (**Table 1**).

#### **3.2 Evaluation of thermal stress**

This stress was evaluated based on the different physical parameters of the thermal environment (air temperature, temperature of the black globe, relative *Ergonomic Evaluation of Thermal Stress in a Tunisian Steel Industry DOI: http://dx.doi.org/10.5772/intechopen.98697*


The working hours - rest limits (K): This duration is calculated in accordance with ISO 7243 "Hot environments - Estimation of the thermal stress of man at work, based on the WBGT index (wet bulb and black globe temperature)" [9]

(2)

<sup>K</sup> <sup>¼</sup> <sup>32</sup> � WBGT 32 � WBGTlim

and according to the following equation:

*Occupational Wellbeing*

◦ Sweat flow in a work situation and during recovery.

◦ Total water loss in the workplace and during recovery

◦ The core temperature reached after 8 hours of work

◦ The time interval to reach a core temperature of 38°C.

◦ The time interval to achieve excessive water loss

but without health risk;

exposure (less than 30 minutes)

predicted heat strain" [10]:

of exposure;

**3. Results**

(**Table 1**).

**70**

**3.1 Study population**

**3.2 Evaluation of thermal stress**

◦ The time interval indicated for drinking 200 cc of water at 10°C

◦ The climatic condition categories in the work situation and during recovery:

a. C1: Comfort category: neither discomfort nor health risk;

b. C2: Discomfort category: discomfort that can be very significant,

d. C4: Short-term stress category: health risk after 30 to 120 minutes

e. C5: Immediate Constraint Category: health risk even for very short

c. C3: Category of long-term constraint: discomfort and risk of

The survey was carried out exhaustively among the operators of the production workshops of the steel company, and included a total of 80 male workers. The mean age was 37.9 � 9.25 years and the mean professional tenure was 12.5 � 11.4 years

This stress was evaluated based on the different physical parameters of the thermal environment (air temperature, temperature of the black globe, relative

Identified in five levels in accordance with ISO 7933 "Analytical determination and interpretation of heat stress using calculation of the

dehydration after several hours of exposure;

humidity, and air speed) as well as on the equivalent metabolism M and the Iclo clothing insulation index evaluated in accordance with the ISO 9920 standard "Ergonomics of the thermal environment - Determination of thermal insulation and resistance to evaporation of a clothing" [7].

	- Mean PMV of 3.2 0.47 with extremes ranging from 1.5 to 4.7.
	- Mean PPD 97.3 3.7% with extremes of 50 to 100%.
