IRSST - Institut de recherche Robert-Sauvé en santé et en sécurité du travail

Impact of Hearing Protection and Hardhats on Auditory Detection and Localization of Vehicle Reverse Alarms


In 2012, the Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST) and the University of Ottawa launched two joint studies comparing conventional reverse alarms (beep...beep signal) with broadband alarms (shh...shh signal) in terms of the safety of workers walking near moving heavy vehicles. The results showed that when the settings are in accordance with ISO 9533, taking into account all ambient noise and not just engine noise, there is no contraindication to the use of broadband reverse alarms, at least for workers with normal hearing and not wearing ear protection. Given the growing popularity of this type of alarm in Québec, the authors wanted to find out whether their results could be applied in actual workplaces, where workers wear passive or active hearing protection as well as other safety equipment such as hardhats.

In this third IRSST/University of Ottawa joint study, the aim was to analyze the ease with which workers were able to hear (detection threshold and reaction threshold) and locate the origin of the two main types of reverse alarm (conventional and broadband) in a set of typical workplace situations, while wearing hearing protectors and hardhats. The methodology was similar to the one used in the second study [Report R-977 (Nélisse, Vaillancourt, Laroche, Giguère and Boutin, 2017)], where the subjects had normal hearing and did not wear hearing protection or hardhats. The detection threshold measurement was aimed at determining the lowest alarm volume that could be perceived against various ambient noises. The reaction threshold measurement was aimed at determining the alarm volume that would cause the worker, against the same ambient noises, to react by turning toward the vehicle or getting out of its way. The location measurement consisted in determining whether the origin of the alarm could be correctly pinpointed and in identifying the types of location confusion (front-back and left-right).

The main results of this study should provide a better framework for the use of reverse alarms and hearing protection in noisy workplaces, taking into account, however, the study limitations stated. Here are the highlights:

  • As was the case in the previous IRSST-funded studies, broadband alarm proved superior to tonal alarm in several respects. Its origin is easier to pinpoint, and it triggers a reaction at a lower S/N (Signal/Noise) ratio, with or without hearing protection.
  • Reaction thresholds are less sensitive than detection thresholds to noise characteristics (spectral and temporal variations). Consequently, it is possible to use an alarm adjustment method based solely on the overall noise level, as prescribed by ISO 9533.
  • If the alarm volume is adjusted according to ISO 9533, it is important to:
  • add up to 7 dB to the 0 dB S/N ratio if hearing protection devices are used. Note that this correction applies only to workers with normal hearing;
  • include all noise sources when measuring ambient noise, not just the engine of the vehicle on which the alarm is installed.


Additional Information

Category: Research Report
Research Project: 2016-0009
Online since: October 09, 2019
Format: Text