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Mobile Equipment Warning Signal Detection in Noise

Mobile Equipment Warning Signal Detection in Noise. Chantal Laroche, Ph.D. A udiology-SLP Program U niversity of Ottaw a. AIHce, June 5 th New Orleans. PROBLEM. Each year, serious accidents occur in noisy workplaces because a warning sound is not heard.

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Mobile Equipment Warning Signal Detection in Noise

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  1. Mobile Equipment Warning Signal Detection in Noise Chantal Laroche, Ph.D. Audiology-SLP Program University of Ottawa AIHce, June 5th New Orleans

  2. PROBLEM • Each year, serious accidents occur in noisy workplaces because a warning sound is not heard. • The bad perception of reverse alarms on mobile vehicles (e.g. dump trucks, forklifts) is one element which can explain some of the accidents. • Potential causes: high levels of ambiant noise, noise-induced hearing loss, lack of attention, placement and acoustic features of alarms, hearing protectors

  3. SOME STATISTICS • Fatal accidents involving workers struck by a machine in motion: - 1980-1992: 667 fatal accidents (USA) (on construction sites; Sweeney et al., 1999) - 1975-2000: > 25 fatal accidents (Quebec) (in reverse mode; Laroche, 2001)

  4. SOME STATISTICS • Serious or fatal accidents involving forklifts: • 1984-1992: 14 deaths (Illinois) • 1991-1992: 24 deaths (OSHA) • 1994-1997: 316 serious accidents (CSST, Quebec) • 1974-1999: 9 deaths (CSST, Quebec)

  5. Employee Type of vehicle Cause of accident Comments flag person (construction site) dump truck reverse alarm not detected alarm: 90dBA; noise from truck: 87dBA quality control attendant (construction site) dump truck reverse alarm not detected alarm in front of the 2 back axles and directed towards the left alarm : 80-85dBA  noise : 105-107dBA worker (road repair) dump truck Absence of reverse alarm? Noise from a mechanical digger Background noise > truck noise Examples of accidents involving mobile vehicles

  6. Examples of accidents involving forklifts

  7. POTENTIAL CAUSES • High level of ambiant noise in the workplace • High prevalence of noise-induced hearing loss (NIHL) • Worker’s attentional demand • Inadequate placement of reverse alarms on vehicles • Deficient acoustic features of existing reverse alarms • Hearing protectors

  8. High levels of ambiant noise • On construction sites: (Suter, 1999) 745 000 (out of 5 million) workers exposed to Lp > 85 dBA Inadequate signalto noise ratio

  9. PREVALENCE OF NIHL • On construction sites: 18 to 33% of workers have hearing thresholds greater than an average of 25 dB at 1, 2, and 3 kHz (Ohlin, 1999)

  10. Worker ’s attention demand and perception • Wilcox (1994) has discussed myths associated with the perception of reverse alarms and the attention demand on forklift trucks: • Pedestrians get used to reverse alarms (habituation phenomenon) • Many forklifts, each equipped with an alarm, would create confusion

  11. Worker’s attention demand and perception • Accidents are caused by a task that demands too much of the victim’s attention • Reverse alarms are annoying

  12. Inadequate placement of reverse alarms • SAE-J994 standard on reverse alarms: « The alarm should be tested in free field, 4 feet above a horizontal reflecting plane, with the microphone 4 feet from the alarm’s horn along its 0 degree axis ». • This standard does not insure that every worker will perceive the alarm at any position behind the vehicle.

  13. Deficient acoustic features • What is found on the market? Reverse alarms with a pure tone (1000-1300 Hz) or modulated tones between two approximate frequencies (e.g. 1272-1310 Hz)

  14. Axis positions behind the heavy vehicles

  15. Positions of the alarm on a grader

  16. Variations in sound pressure levels at the rear of a grader

  17. Sound wave reflections

  18. Hearing protection • Sense of insecurity frequently reported: Difficulty to hear and understand speech communication and warning signals

  19. Recommendations • In order to reduce the number of fatal accidents involving pedestrians at the rear of vehicles: • Modifications in the design and positioning of reverse alarms • Avoid pure tones • Optimize the position • Better ergonomic design of mobile equipment • Addition of pedestrian corridors, when possible

  20. Recommendations (cont’d) • Explore ways to limit the habituation phenomenon • Obstacle detectors • Use of electronic mirrors There is a need for improvement in the reliability of these devices • Noise reduction in the workplace • Would reduce the prevalence of NIHL • Would reduce the masking effect of the background noise

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