Given that conversation in the work environment is a means of communication, the presence of background noises or noises close to the frequencies of conversation, especially in office environments, can disrupt communication between employees and even interference the conversation [1, 2]. The use of hearing protection devices (HPDs) can affect employees' speech intelligibility in noisy environments. Furthermore, the acoustic data of HPDs is one of the significant challenges for occupational health experts to assess the exposure levels of employees to noise. The amount of nominal noise reduction rating(NRR) of these devices, which is generally provided by the manufacturing companies in the identification card of these pieces of equipment, is mostly different compared to their actual noise reduction rating [3, 4, 5]. Among some methods disclosed for determining HPDs noise reduction, Berger et al. proposed the Real-ear attenuation at threshold (REAT) hearing threshold method as the best and most accurate method based on the individuals' subjective responses [6, 7, 8].
Previous studies showed that, the irregular use of HPDs in work environments can be due to difficulty in communication. For employees, communication with colleagues and also hearing signals from the equipment and devices is of great importance [9, 10, 11]. Nelisse et al. determined that only 64% of employees in that environment used HPDs, and only 20% used them consistently during full shifts. Some the main reasons why employees did not use hearing protectors consistently were loss of their performance, lack of comfort, and interference in conversations with colleagues [12]. Hasahimito et al. revealed that a decrease in the noise reduction rates of hearing protectors cannot be considered as a factor for improving speech intelligibility [13]. Fernandes et al. showed that at the lowest background noise levels (60 and 70 dBA), HPDs reduced speech intelligibility while the background noise levels were approximately between 80 and 90 decibels and the signal to noise ratio (0, -5, and − 10 decibels), HPDs improved speech intelligibility [14].
In developing countries, occupational health experts also reported that unreliable data of HPDs are considered the main challenge to achieve an efficient hearing conservation program [4].The consequences of hearing protectors on verbal communication and speech intelligibility are of great importance in typical office work environments. Less attention has been paid about the speech intelligibility result from using HPDs in Persian office work environments. This study aimed to investigate the effect of hearing protection devices on speech intelligibility of Persian employees in the simulated office noise emission.