Abstract:
Machine shop workers are exposed to noise levels between 83 - 110 dB(A), however, levels above 85 dB (A) are hazardous to the ear. A study was conducted at GRATIS Foundation in Tema Industrail Area in Ghana, using sound level meters to determine noise levels and propose solutions. Sound levels during peak hours of operation in the machine shop were found to be above 95 dB(A). To reduce these high noise levels, Coconut Fibre (CF) a naturally occurring sound absorber, was combined with Polyvinyl Chloride Sheets (PVCS) or “Flexi Banner” to create a sound insulating panel. These combinations: CF, “PVCS + CF”, “PVCS + CF + PPVCS” and “PVCS + CF +PVCS” were tested in the lab for sound Insertion Loss (IL) and Transmission Loss (TL). In the test, CF thicknesses (10, 20 and 30 mm) were varied and 10 Octave band center frequencies of sound between 31.5 to 16000 Hz passed through the specimens. Analysis of Variance on results for TL test concluded that, thickness, frequency, and combination sequence (CS) and Frequency (FQ) interactions, had significant effect on TL, from 1000 – 16000 Hz. CS of PVC + 30 mm CF + PVC was selected as the CS with the most TL over the frequency range. With respect to IL test, it was concluded that, CS, Thickness, FQ, and CS and FQ interactions, also had significant effect on IL. PVCS + 30 mm CF + PVCS was selected for its high IL for higher frequencies from 4000 to 16000 Hz. It was also noted that, PVCS + CF + PPVCS could be used in place of PVCS + CF + PVCS to achieve similar IL averages, over the frequency spectrum. By combining CF with PVCS, it increased its TL by 24.5 dB(A) and IL by 26.02 dB(A) at 8000 Hz. After insulating the highest noise source in the machine shop (hand Held Grinder) with PVCS + 30 mm CF + PVCS, sound levels ranges dropped from 75 - 105 dB(A) (beyond standards) to 65 - 85 dB (A) range (safe zone). Hence, abating noise in the machine shop through combined CF and PVCS was successful
