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

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Reverse Alarms: Broadband Stands Out Again


Reverse Alarms: Broadband Stands Out Again

Broadband alarms appear to be more effective than tonal alarms in alerting workers to danger, whether or not they are wearing hearing protectors or hard hats.

Heavy vehicles in motion create their own series of challenges in terms of occupational health and safety. Every year in Québec, back-up manoeuvres cause accidents, some of them fatal, in several fields of activity such as transportation and mining, and in municipal garages.

One of the most commonly used means to prevent these accidents is the use of reverse alarms, which are obligatory for most heavy vehicles. Their characteristic “beep beep” when a vehicle backs up alerts the workers in the vicinity.

However, as Chantal Laroche, professor in the Faculty of Health Sciences at the University of Ottawa, points out, in practice these tonal alarms are far from perfect. “The pure tones of this type of alarm can easily be disrupted: sound waves bounce off obstacles or the ground before reaching the workers. This acoustic interference causes sound variations of up to about 20 decibels over short distances, meaning that workers can be mistaken about where the vehicle actually is,” she explains.

When workers are unable to accurately pinpoint where vehicles are backing up, they could be struck or run over. The effect may be more pronounced if they are wearing hearing protectors and hard hats, as is often the case on construction sites.

A Third Research Study

This third joint research study by the IRSST and the University of Ottawa on reverse alarms analyzes the audibility and the accuracy of localization of two major types of alarms, one of which is the broadband model. “Its distinctive “pshhhh… pshhhh…” is more evenly transmitted behind vehicles than the sound emitted by a tonal alarm. We are starting to see more of this type of alarm here in Québec,” adds the psychoacoustic expert.

Experiments have been carried out involving people with normal hearing and a range of typical worksite situations in which heavy vehicles with reverse alarms are likely to be operating, such as quarries, mines, sawmills, and construction worksites. Various hearing protectors, both hard-shell earmuffs and earplugs, were used. The effect of hard hats on the detection threshold, reaction threshold and localization was also tested, even though the researchers suspected that it would be minimal, which turned out to be the case.

The wearing of hearing protectors leads to an increase in reaction thresholds, no matter the type of alarm.

A Predictable Difference

As in the previous research funded by the IRSST, broadband alarms have again demonstrated their superiority over tonal alarms. The participants found them easier to localize and reacted to a lower sound level, with or without hearing protectors. “To trigger the same reaction, tonal alarms must be a few decibels higher, which needlessly increases the cacophony and noise pollution,” says Chantal Laroche.

The other main conclusion of the research is that wearing hearing protectors causes reaction thresholds to rise, no matter the type of alarm. As a result, the overall sound level must be louder to spur the desired reaction of moving out of the way. “In our study, we’re talking about an increase of approximately 5 to 7 dB compared to the background noise. But these values are specific to the protectors that we used and are only applicable to people with normal hearing,” qualifies the researcher.

Learn more

VAILLANCOURT, Véronique, Chantal LAROCHE, Christian GIGUÈRE, Hugues NÉLISSE. Effet du port de protecteurs auditifs et de casques de sécurité sur la perception et la localisation auditives des alarmes de recul, R-1067, 99 pages.