The effect on earmuff attenuation of other safety gear worn in combination

This study assessed the effect of other safety gear worn in proximity on the attenuation afforded by earmuffs attached to a hard hat. Seventy-two males and females participated: 24 under the age of 40 years with normal hearing, and 48 over the age of 40 years, half with normal hearing and half with bilateral high-tone hearing loss. Measurements were made with the ears unoccluded, with the muffs on hard hat alone, and with the muffs on hard hat in combination with safety glasses, an air-purifying half mask respirator or both glasses and respirator. They included (1) diffuse field hearing thresholds from 0.25-8 kHz, and (2) consonant discrimination in quiet and in 80-dB SPL speech spectrum noise. Attenuation was derived by subtracting the unoccluded from the protected hearing threshold at each frequency. Muff attenuation was within 6 dB of the manufacturer's specifications but decreased by as much as 5 dB when the glasses or respirator were worn and by 9 dB with both these devices. Males achieved 3 dB higher attenuation than females. However, hearing status had no effect. Consonant discrimination was significantly worse in noise. The impaired subjects performed more poorly when wearing the muff on hard hat but there was no additional effect of wearing the glasses and/or respirator. These results demonstrate that wearing other protective safety gear around the head can interfere with the hearing protection provided by earmuffs. They also confirm that for people with a hearing loss, the use of earmuffs may increase the communication handicap.