[Comparison of noise protection effects of two common types of earplugs]

Objective: To compare the protective efficacy and influencing factors of 1100 foam earplugs and 1270 preform earplugs, and to investigate the spectral characteristics of sound attenuation for these two types of earplugs. Methods: In January 2023, a cluster sampling method was employed to select 306 noise-exposed workers in the automotive manufacturing industry as study subjects. Basic worker information and hearing protection device usage were collected via questionnaire surveys. The 3M(TM) E-A-R fit(TM) dual-ear protection verification system was used to assess earplug suitability, with one-on-one training provided to workers who failed the baseline personal attenuation rating (PAR) test. The spectral characteristics of sound attenuation for both earplugs were analyzed using PAR(50) (with a protection rate of 50%). Mann-Whitney U test and Chi-square test/Fisher's exact probability method were used to compare the changes in PAR and pass rate of the two types of earplugs. Results: The baseline PAR values M (Q(1), Q(3)) for workers wearing 1100 foam earplugs and 1270 preform earplugs were 19 (14, 23) dB and 0.5 (0, 12) dB, respectively, and the baseline PAR pass rates were 84.8% (178/210) and 37.5% (36/96), respectively. The differences were statistically significant (P<0.001). Age, years of service, noise exposure intensity, and correct wearing training had statistically significant effects on the baseline PAR pass rate of 1100 foam earplugs (P<0.05), but had no statistically significant effects on the baseline PAR pass rate of 1270 preform earplugs (P>0.05). After the intervention, all workers passed the suitability test. There were differences in PAR(50) values at different frequency bands between the two types of earplugs. The measured values of 1100 foam earplugs at 125-250 Hz were lower than the nominal values, indicating poor protective effect; the measured values at 250-8000 Hz gradually approached the nominal values, indicating a better protective effect. The measured values of 1270 preform earplugs at 125-250 Hz were close to the nominal values, indicating a better protective effect; however, the measured values at 250-2000 Hz fluctuated greatly, and the measured value at 4000 Hz differed significantly from the nominal value, indicating a poorer protective effect. Conclusion: The overall noise reduction effect of 1100 foam earplugs is better than that of 1270 preform earplugs. Training on wearing methods is crucial for improving the wearing effect, 1100 foam earplugs require better wearing skills. 1100 foam earplugs have better protective effects in the mid-to-high frequency bands, while 1270 preform earplugs have better protective effects in the low frequency band.