Experimental assessment of the effect of wearing hearing protectors on the audibility of railway warning signals for normal hearing and hearing impaired listeners

Abstract

The influence of wearing hearing protectors on the detection of seven railway warning signals in noise was evaluated by comparisons of the masked thresholds measured with and without hearing protectors, out of a total of 80 listeners. The results show that wearing hearing protection devices (HPDs) improves the audibility for normal hearing listeners whereas it tends to impede the audibility for hearing impaired listeners. Moreover, the impediments greatly depend on the warning signal acoustical characteristics. Statistical analyses were performed in order to propose a criterion for hearing impaired listeners that guarantees their security when wearing hearing protectors. If we do not consider one given high-pitched signal that is not suitable as a warning signal, the conclusion is that security is assured when the average absolute hearing threshold (average at 500, 1000 and 2000 Hz for the best ear) of the listeners remains lower than a hearing level of 30 dB.

Keywords:

• hearing protector devices
• warning signals
• audibility
• masked threshold
• hearing impaired

Acknowledgements

The authors are grateful to and acknowledge the SNCF occupational health services and prevention services for providing and caring for the agents who took part in the study.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1 AIP stands for ‘Audibility, speech Intelligibility or Perception of informative operating sound’.

2 For each box, the central mark indicates the median, and the bottom and top edges of the box (of numerical values q1 and q3, respectively) indicate the 25th and 75th percentiles, respectively. The whiskers extend to the most extreme data points not considered outliers, and the outliers are plotted individually using the '+' symbol. The data points are drawn as outliers if they are greater than q3 + 1.5 × (q3 – q1) or less than q1 – 1.5 × (q3 – q1).

3 The up arrow was chosen to indicate a threshold elevation when HPDs are worn (as compared to no HPD).