Sound Research Ventures Pty Ltd – November 2002

This report presents the results of a Coal Services Pty Ltd Health and Safety Trust funded project titled “Working Safely with Hearing Loss”. The project arose from the need to develop a reliable procedure for testing whether underground coal miners with a high degree of hearing loss could hear adequately in the work environment for safety purposes. It is vitally important that all workers be able to respond appropriately to warnings during an emergency situation. A worker who has significant loss of hearing, as defined through audiometric testing, is assumed to be less capable of hearing warnings and is therefore considered a risk to himself and others.

While this would certainly be the case for a profoundly deaf person or a person who has lost part of their hearing through a sudden trauma, workers who have sustained ‘industrial deafness’ over a long period of time partially adapt to the condition and can often hear much better during normal conversation than their audiograms would suggest. This adaptation is due to the greater conscious effort to listen and the use of visual cues such as lip-reading and observing the speaker’s body language. These visual cues are generally not presented underground and the true
effect of the hearing loss is uncertain.

Another important factor affecting the audibility of shouted warnings is the presence of high background noise levels. Even people with little or no hearing loss find it difficult to hear speech in a noisy environment. This project therefore investigates the ability of work-aged people with hearing loss to hear verbal commands in a noisy, underground environment. No attempt is made to determine the absolute level to which the underground environment affects speech intelligibility. Rather, the focus is on the reduced hearing ability of the ‘industrially deaf’ worker compared to that of a worker with little or no loss of hearing.