SIIT Commemorative Publication (10 Years of International ...

10 Years of International Cooperation: FTI, Nippon Keidanren and TUSIIT Commemorative Publication, 2002control approach are not easy to implement. Forexample, it is recommended that workers rotate amongworkstations to reduce their daily noise exposurelevels. Since there are numerous combinations of workassignments to consider, it is almost impossible for thesupervisor to find the optimal work assignmentsolution.An Excel-based computer program called “NoiseManager” is developed to assist safety practitioners topractically implement several recommendations basedon the administrative approach. Noise Manager can beused to evaluate existing noise conditions andrecommend practical solutions. It consists of eightmodules. The first four modules are for noiseevaluation and the last four are for noise management.The user can select the preferred module from themenu as shown in Fig. 190n ⎡ L j − ⎤D T = 12.5 C 25∑⎢ ⎥j(2)j=1⎢ ⎥⎣ ⎦3.2 Module 2 – Calculation of Noise Level andPermissible Duration at any LocationTo predict the combined noise level at any location,Noise Manager needs information such as the ambientnoise level, noise levels of all noise sources in the workarea, and the locations (in x and y coordinates) of thosenoise sources. The following formula can be used todetermine the combined noise level at location i ( L i ).L i =⎡n ( Lj−120)/10( 120)/10 10 ⎤Lab−10log ⎢10 + ∑ ⎥+1202⎢⎣j=1 dij⎥(3)⎦where d ij is the distance between location i and noisesource j, L j the noise level of noise source j, and L ab theambient noise level.If the worker is required to be at one location for theentire day, it is possible to determine the permissibleexposure time (T) at that location from the known noiselevel.−1−90⎡ L ⎤5T = 8(4)⎢2⎣⎥⎦Fig. 1 Noise Manager and its modules.3.1 Module 1 – Calculation of TWA and Noise Doseof an 8-hour DayA time-weighted average (TWA) is an index thatmeasures the amount of long-term noise exposure. Todetermine the 8-hour TWA, Noise Manager needs toknow the noise levels at the locations that the worker ispresent and the exposure duration at those locations. Itthen uses the following formula to calculate the 8-hourTWA (W) in dBA,3.3 Module 3 – Construction of Noise Contour Mapof a FacilityA noise contour map depicts noise levels at variouslocations in the work area. Usually, locations that havethe same noise level are connected together by thesame contour line. To analytically construct a noisecontour map, Eq. (3) can be used to determine thecombined noise level. Figure 2 shows an example of a3-dimensional noise contour map constructed by NoiseManager.W =⎡ ⎧90nLC ⎛ j − ⎞⎫⎤j16.61⎢ ⎪log ⎜2 5 ⎟ ⎪⎥+ 90⎢ ⎨∑ ⎬(1)j=1 8 ⎜ ⎟ ⎥⎢ ⎪ ⎝ ⎠⎪⎣ ⎩⎭⎥⎦where C j and L j are the exposure duration and thecombined noise level at workstation j, respectively.The daily noise dose (D T ), in percent, can also becalculated using the same data. The daily noise doseand the 8-hour TWA present similar information aboutthe noise condition (Nanthavanij 1998).Fig. 2 A noise contour map.78