Workers’ exposure to occupational heat during manual coffee harvesting

This study evaluated the occupational exposure of workers to heat during manual harvesting of coffee. The case study was conducted between May to August. Occupational heat in coffee plantations was evaluated using the Wet Bulb Globe Temperature (WBGT) method and the metabolic rate. The WBGT was obtained using the TGD 400 thermal stress meter. The determined WBGT values were compared to two standards: the Occupational Hygiene Standard (NHO) 06 and Regulatory Norm (NR) 09. For acclimatized workers, the exposure limit was not exceeded at any time during the evaluated period. Fornon-acclimatized workers, the exposure limit was not exceeded only in July.

to heat including the workers' thermal overload, action level, exposure limit, and acclimatization, was used.
The evaluation of occupational heat exposure was performed by simulating a worker performing the activities involved in manual coffee harvesting such as the tasks of opening the cloth, stripping the coffee fruit, shaking it to remove impurities, filling the bags, and transporting them to the big containers. The metabolism rate determined according to NHO 06 for moderate manual work, was used to simulate a worker performing the activities involved in manual coffee harvesting (FUNDACENTRO, 2017) and the measured rate was 468 W.
The data were collected using a heat stress meter with 0.1 ºC resolution and ± 0.5 ºC accuracy (MOD: TGD -400), consisting of wet bulb (wbt), dry bulb (dbt), and globe thermometers (gt). The equipment was mounted on a tripod and installed at a central point of the field with greater sun exposure and the thermometers were positioned at a height of 1.70 m, which is considered the median height of the workers by the IBGE (2009). The evaluations were performed on days with no clouds to avoid the influence of shading at the evaluation point (FUNDACENTRO, 2017).
The data were collected by the data logging system of the equipment, which quantified the Wet Bulb Globe Temperature (WBGT) at every 60 minutes, between 7:00 am and 4:00 pm, with a total of four days of evaluations in each of the months studied (May/June/July/August). (2017) and the American Conference of Governmental Industrial Hygienists (ACGIH, 2018), the WBGT evaluation with solar load was expressed in °C, (Equation 1) as follows: WBGT = 0.7 wbt + 0.2 gt + 0.1 dbt wbt= natural wet bulb temperature (ºC) gt= globe temperature (ºC) dbt= dry bulb temperature (air temperature ºC).

As determined by Fundacentro
The WBGT values obtained were compared with two norms, the NHO 06 and the NR 09. These standards determine the action level and exposure limit for non-acclimatized workers to be 22.1 °C and the exposure limit for acclimatized workers to be 25.9 °C, for performing activities with a metabolic rate of 468 W. It is noteworthy that acclimatized workers are defined as those who have undergone physiological adaptation by means of successive and gradual heat exposures that aim to reduce the thermal overload caused by thermal stress (FUNDACENTRO, 2017).
The WBGT data were subjected to the Shapiro-Wilk test for normality analysis. The data presented normal distribution (P > 0.05) and were subjected to analysis of variance. The interaction between the evaluated months and times was analyzed. The data were subjected to the Scott-Knott test at 5% significance using the R software version 3.2.4 (R CORE TEAM, 2016).
There was a significant effect in the interaction between the evaluation times and months on the mean WBGT index value (gl = 24; HR = 1.31; P < 0.05) ( manual coffee harvest for the months evaluated were recorded from 7:00 am to 7:59 am. The most unfavorable thermal conditions for May, July, and August were found after 11:00 am. However, there was a WBGT reduction in May from 3:00 pm to 3:59 pm, with 19.59 ºC. In June, the highest WBGT index was recorded between 9:00 am to 3:59 pm. The most unfavorable working conditions should be observed and measures adopted to prevent occupational heat exposure (FUNDACENTRO, 2017;ACGIH, 2018).
Comparing the data obtained to that of the NHO 06 and NR 09, the results showed that the occupational exposure limit for acclimatized workers was not exceeded at any time during the workday in the months evaluated (Figure 1). The same results were reported for non-acclimatized workers in July when there were no recorded values above the exposure limit. However, the values obtained in May from 11:00 am to 2:59 pm, June from 10:00 am to 2:59 pm, and August from 12:00 to 2:59 pm, were above the exposure limit for non-acclimatized workers (Figure 1).
Under the study conditions, the most unfavorable thermal conditions were observed between 11:00 am and 2:59 pm in the months evaluated. For acclimatized workers, the exposure limit was not exceeded at any time during the evaluated periods. In May, June, and August, non-acclimatized workers were exposed to heat above the exposure limit.