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

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

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

SOME STATISTICS Serious or fatal accidents involving forklifts: – : 14 deaths (Illinois) – : 24 deaths (OSHA) – : 316 serious accidents (CSST, Quebec) – : 9 deaths (CSST, Quebec)

Examples of accidents involving mobile vehicles EmployeeType 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 : dBA worker (road repair) dump truck Absence of reverse alarm? Noise from a mechanical digger Background noise > truck noise

Examples of accidents involving forklifts EmployeeCause of accidentRecommendations Seagoing personnel- High level of noise - Low visibility (dead angle) - Pedestrians and vehicles - Noise control - Mirors - Delimit pedestrian corridors Student, Maintenance -Low visibility -Bad judgment No specific recommendantion

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

High levels of ambiant noise On construction sites: (Suter, 1999) (out of 5 million) workers exposed to Lp > 85 dBA Inadequate signal to noise ratio

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)

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

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

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.

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

Axis positions behind the heavy vehicles

Positions of the alarm on a grader

Variations in sound pressure levels at the rear of a grader

Sound wave reflections

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

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

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