Analysis of the differences and influencing factors of occupational noise exposure level assessed by two different methods

  Objective  To observe the difference of occupational noise exposure level calculated according to area sampling and individual sampling, in order to explore influencing factors between two methods.

  Methods  According to the standard of GBZ/T 189.8-2007 Measurement of Physical Agents in Workplace Part 8: Noise, 8 hour equivalent sound level of 290 employees in 52 machinery manufacturing enterprises were measured by individual sampling and area sampling to assess noise exposure. Paired sample t test and paired χ² test were used to compare the test results and non -compliance rate compared with national exposure limit of the two methods. Paired sample t test was used to analyze the differences between two results in different work types and operation modes. Independent sample t test and linear mixed effects model were used to explore the influencing factors of the differences between two results.

  Results  The mean value of 8 h equivalent sound level based on area sampling of 290 workers was 83.5 dB (A) with non -compliance rate of 36.9%. The mean value of 8 h equivalent sound level based on individual sampling of 290 workers was 85.9 dB (A) with non-compliance rate of 52.1%. The mean value and non-compliance rate of 8 h equivalent sound level based on individual sampling were higher than that based on area sampling (P < 0.05). Stratified by work type and operation mode, the mean value of 8 h equivalent sound level of lathe workers and welders based on individual sampling was higher than that based on area sampling (P < 0.05). The mean value of 8 h equivalent sound level of workers with fixed operation based on individual sampling was higher than that based on area sampling(P < 0.05), while the mean value of 8 h equivalent sound level of workers with mobile operation based on individual sampling was lower than that based on area sampling(P=0.002). The results of the linear mixed effect model showed that the mean value of the difference between two results of welders was 1.7 dB(A) higher than that of lathe workers(β=1.7, 95%CI: 0.4-3.0, P=0.012). The mean value of the difference between two results of workers with mobile operation was higher than workers with fixed operation, but the difference was not statistically significant (β=0.7, 95%CI: -1.1-2.5, P=0.452).

  Conclusions  There are differences in occupational noise exposure assessment results between area sampling and individual sampling. Work type and operation mode could affect the differences of two results. Individual sampling should be recommended for the occupational noise exposure assessment in welders with mobile operation.