Mobile Equipment Warning Mobile Equipment Warning Signal Detection in NoiseSignal Detection in Noise

Chantal Laroche, Ph.D.Chantal Laroche, Ph.D.AAudiology-SLP Programudiology-SLP Program

UUniversity of Ottawniversity of Ottawaa

AIHce, June 5th

New Orleans

PROBLEMPROBLEM

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 STATISTICSSOME STATISTICS

Fatal accidents involving workers struck by a machine in motion:

- 11980-1992: 667 fatal accidents 980-1992: 667 fatal accidents ((USA)USA)

(on construction sites; Sweeney et al., 1999)(on construction sites; Sweeney et al., 1999)

- 1975-2000: > 25 fatal accidents (Quebec)- 1975-2000: > 25 fatal accidents (Quebec)

(in revers(in reversee mode; Laroche mode; Laroche,, 2001) 2001)

SOME STATISTICSSOME STATISTICS

Serious or fatal accidents involving forklifts:

– 1984-1992: 14 deaths 1984-1992: 14 deaths (Illinois)(Illinois)– 11991-1992: 24 deaths 991-1992: 24 deaths (OSHA)(OSHA)– 11994-1997: 316 serious accidents 994-1997: 316 serious accidents

(CSST, (CSST, Quebec)Quebec)– 11974-1999: 974-1999: 99 deaths deaths (C(CSSST, Quebec)ST, Quebec)

EExamples of accixamples of acciddents ents involving mobile vehiclesinvolving mobile vehicles

 

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

 

EExamples of accixamples of acciddents ents involving forkliftsinvolving forklifts

Employee Cause of accident Recommendations

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

POPOTTENTIAL CAUSESENTIAL CAUSES

High level of ambiant noise in the workplaceHigh level of ambiant noise in the workplaceHHigh prevalence of noise-induced hearing loss igh prevalence of noise-induced hearing loss

(NIHL)(NIHL)WWorker’s attentional demand orker’s attentional demand IInnaadequate placement of reverse alarms on vehidequate placement of reverse alarms on vehiccleslesDDeficient acoustic features of existing reverse alarmseficient acoustic features of existing reverse alarmsHearing protectorsHearing protectors

HigHighh levels of ambiant noise levels of ambiant noise

On construction sites: (Suter, 1999)

745 000 (out of 5 million) workers exposed to Lp > 85 dBA

Inadequate signal to noise ratio

PREVALENCE OF NIHLPREVALENCE 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 Worker ’s attention demand and perceptionand 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 Worker’s attention demand and perceptionand perception

– Accidents are caused by a task that demands too much of the victim’s attention

– Reverse alarms are annoying

Inadequate placement of Inadequate placement of reverse alarmsreverse 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 featuresDeficient 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)

Axis positions behind the Axis positions behind the heavy vehiclesheavy vehicles

Positions of the alarm Positions of the alarm on a graderon a grader

Variations in Variations in sound pressure levels sound pressure levels at the rear of a graderat the rear of a grader

Sound wave reflectionsSound wave reflections

Hearing protectionHearing protection

Sense of insecurity frequently reported:

Difficulty to hear and understand

speech communication

and warning signals

RecommendationsRecommendations

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)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