Individual Fit Testing of Hearing-Protection Devices Based on Microphones in Real Ears among Workers in Industries with High-Noise-Level Manufacturing

Abstract

Hearing-protection devices (HPDs) are particularly important in protecting the hearing of workers. The aim of this study was to prevent hearing damage in workplaces in Taiwan. It was conducted to determine the actual sound attenuation of the personal attenuation rating (PAR) values when wearing HPDs via measurements from field microphones in workers' real ears (F-MIRE). Across 105 measurement trials for the Classic™ roll-down foam earplug HPDs worn by the workers, there were 23 cases of ineffective protection (including caution and fail); the proportion was 20% (including the first measurement and re-wear of HPDs after education and training). In addition, re-education and training in how to wear the HPDs was provided, improving wearing skills. A total of 29 testees wearing the Classic™ roll-down foam earplug HPDs failed to meet the pass standard for the first PAR test, and 6 of them improved and subsequently passed the PAR test. The improvement rate was 20%. These 23 testees switched to another HPD, namely Kneading-Free Push-Ins™ earplugs. From this group, 16 effective sound attenuation values were obtained, with an improvement rate of 70%. However, seven testees failed to pass the PAR test, and after education, training, and replacement of HPDs with different types, they still could not pass the PAR test. At that time, even if the UltraFit™ pre-molded earplugs were adopted again for wear and replacement, they were still unable to pass the PAR test. This HPD was eventually replaced with the PELTOR X4A Earmuff HPD and then tested again, with these HPDs finally passing the PAR test. In Taiwan, the use of fit testing has been increasing but it is not a common practice, and few studies on hearing-protection fit testing have been conducted in this country. The goal of this study was to gain more insight into the current hearing protection situation, including field attenuation of HPDs obtained by workers, the effects of training on improving the attenuation of HPDs after F-MIRE measurements, and the awareness of hearing health and motivation on the use of HPDs in a high-noise-level environment.

Keywords: field microphone in real ear (F-MIRE); hearing-protection device (HPD); noise exposure; personal attenuation rating (PAR); pre-workforce education.

Figure 1

The equipment used in the F-MIRE test method in this study.

Figure 2

Schematic diagram for the measurement location in the evaluation of the attenuation of HPDs via the F-MIRE test method. ✽ Remarks: insertion loss (IL) = A − A′ ≌ REAT; noise reduction (NR) = B′ − A′; TFOE is measured with respect to Point B, which is generally the head-center location with the head absent. NR = IL − TFOE.

Figure 3

The flowchart of the evaluation process for the 3M™ EA-RfitTM HPD adaptability evaluation system applied in this study.

Figure 4

An example where the test result of the PAR value was “fail” in the first test in the untaught situation of the testee.

Figure 5

An example where the test result of the PAR value was “pass” after additional instructions and a different type of HPD were provided, followed by a re-test of the adaptability with the new HPD.

Figure 6

The distance from the testee’s nose to the clip on the loudspeaker was 40 cm.