Evaluation of occupational exposure to wood dust and noise among sawmill workers in the Gert Sibande district municipality

Abstract

Wood dust is a human carcinogen based on an increased risk of nasal and sinonasal cancer. Occupational exposure to hazardous noise above the 85 decibels, A-weighted (85 dB[A]), eight-hours time-weighted average (8-hour TWA) can cause noise induced hearing loss (NIHL). The aim of the study was to measure and determine the timeweighted average (TWA) occupational exposure level (OEL) to wood dust and noise and compare the results with the OEL for wood dust and the noise rating limit for noise and assess hearing loss and respiratory symptoms and use of personal protective equipment (PPE) among sawmill workers within the Gert Sibande District Municipality. A comparative cross-sectional study comprising of 137 exposed and 20 unexposed workers randomly selected, using simple random sampling was undertaken between January and March 2021. Self-reported hearing loss and respiratory symptoms were evaluated using a self-administered questionnaire. Personal and area wood dust exposure levels were measured using calibrated Giliair-3 personal air sampling pumps, while personal and area noise surveys were conducted using calibrated SV104IS noise dosimeters (SVANTEK, Poland) and a type 1 sound level meter (Soundpro SE/DL, U.S.A.). Data was analysed using the Microsoft Excel 2019 analysis Tool Pak to obtain a summary of descriptive statistics. The geometric mean, standard deviation, minimum and maximum values were calculated. Mann-Whitney U test was used to test the significance of the differences between values in sawmill A and B while t-test was used to compare the mean time-weighted averages of occupational exposure levels to noise from sawmills A and B. Discrete data from questionnaire results were presented as percentages and tables. The t-test was used to compare continuous variables, while the chi-square test was used to test categorical responses. Fisher's test was employed when the anticipated number was below 5. A significance level of 0.05 was used. The prevalence of symtoms such as chest pains or shortness of breath was higher among the unexposed group (50%) than the exposed group (44%). Furthermore, the participants in the exposed group suffered from tinnitus (ringing in the ears) (50%) and ear infections (21.43%). Moreover, the unexposed group reported suffering from tinnitus (33%) and ear infections (66.67%). The exposed group (86.86%) reported always wearing the personal protective equipment (PPE) than the unexposed group (75%) who wear it sometimes. Moreover, the exposed group (48.48%) did not wear PPE consistently due to not being available while all participants from the unexposed group reported other reasons for not wearing it. The geometric mean(GSD) for personal respirable wood dust exposure level at sawmill A was 0.9(4.8) mg/m3 while at sawmill B was 0.57(0.75) mg/m3 . The geometric mean(GSD) for personal respirable wood dust exposure level at sawmill A was 0.9(4.8) mg/m3 while at sawmill B was 0.57(0.75) mg/m3 . The geometric mean(GSD) for personal total inhalable wood dust exposure level at sawmill A was 0.37(0.94) mg/m3 while at sawmill B was 1.19(16.91) mg/m3 . Moreover, the geometric mean(GSD) for area respirable wood dust exposure at sawmill A was 0.13(0.09) mg/m3 while at sawmill B was 0.8(0.6) mg/m3 . Likewise, the geometric mean(GSD) for area total inhalable wood dust exposure at sawmill A was 0.13(0.16) mg/m3 while at sawmill B was 0.54(0.55) mg/m3 . The geometric mean(GSD) for area noise exposure level at sawmill A was 90.05(8.02) dB(A) while at sawmill B was 90.14(7.94) dB(A). The geometric mean(GSD) for personal noise exposure level at sawmill A was 92.26(4.35) dB(A) while at sawmill B was 92.24(2.65) dB(A). Occupational exposure to wood dust and noise was associated with respiratory symptoms such as chest pains or shortness of breath and hearing loss conditions or symptoms such as tinnitus (ringing in the ears) and ear infections (Ha accepted and H0 rejected). The majority of the results for wood dust samples were below the South African OEL, while majority of the results for noise exposure levels were above the noise rating limit (Ha accepted and H0 rejected). A non-significant difference on the levels of exposure to noise was observed when comparing the results of sawmill A to sawmill B (H0 accepted and Ha rejected). Similarly, a non-significant difference on the levels of exposure to wood dust was observed when comparing the results of sawmill A to sawmill B (H0 accepted and Ha rejected). The findings suggest that sawmill owners should take steps to lower the levels of exposure to noise and wood dust to help protect workers’ health.Implementation of engineering and administrative controls supplemented by appropriate use of the fit-tested hearing protective devices (HPDs) with the higher noise reduce reduction (NRR) or single number rating (SNR) and the respiratory protection devices (RPDs) with the higher assigned protection factor (APF) is recommended based on the exposure levels recorded. Tobacco or cigarette smoking should be discouraged because when associated with exposure to wood dust and noise may increase risk of respiratory symptoms and development of high frequency hearing loss.