Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Sound localization wikipedia , lookup
Hearing loss wikipedia , lookup
Auditory system wikipedia , lookup
Soundscape ecology wikipedia , lookup
Audiology and hearing health professionals in developed and developing countries wikipedia , lookup
Sound from ultrasound wikipedia , lookup
Tools for optimizing the installation of warning sounds in noisy workplaces Chantal Laroche, Christian Giguère, Rida Al Osman and Yun Zheng 2010 NHCA Conference February 25-27, 2010 Background Safety in the workplace: Noise is a key hazardous factor and can cause hearing loss Acoustic warning signals are crucial to alert workers and reduce the risk of accidents Safety is dependent on alarm recognition and communication ability in the presence of background noise Hearing protectors: Minimize the adverse effects of noise in the workplace … BUT Can compromise the audibility of warning signals 2010 NHCA Conference – Orlando, Florida February 25-27, 2010 Background Current practices for installing warning devices: ISO 7731: “Danger signals for public and work areas” Devices typically installed on walls or ceiling at a certain distance from workstations Installation is poorly regulated and submitted to intuition Factors that must be taken into consideration: Audibility in the workplace Sound propagation from the device to the various workstations (direct sound path and reflected sound waves) Noise field (level, spectrum, type) Warning signal design (frequency components, level) Number, location and sound power level of warning devices Effects of hearing status (hearing thresholds, frequency selectivity) and hearing protectors 2010 NHCA Conference – Orlando, Florida February 25-27, 2010 The problem How many alarm devices needed? Where? 2010 NHCA Conference – Orlando, Florida February 25-27, 2010 Sound power level? General Framework WORK ENVIRONMENT Room layout, Reverberation time, Workstation coordinates (Xk, Yk, Zk) WORKERS Hearing Frequency thresholds selectivity Warning signal target levels [TLlow , TLup ] AlarmLocator Number Coordinates Power level (Xi, Yi, Zi) ND Lw WARNING DEVICES 2010 NHCA Conference – Orlando, Florida February 25-27, 2010 Detectsound Noise Lp HPD attenuation WORKSTATIONS Detectsound The outcome of “Detectsound” is a design window for warning sound levels at each workstation W 110 Window: dB SPL 100 De sign window TLup = THR + 25 dB 90 TLlow = THR + 12 dB 80 Background noise TLmax = 105 dB SPL 70 60 125 200 315 500 800 1250 2000 3150 Frequency (Hz) 2010 NHCA Conference – Orlando, Florida February 25-27, 2010 AlarmLocator The outcome of “AlarmLocator” is a solution of warning devices (D) to meet “Detectsound” targets at all workstations (W) Simulations: Mirror image method (early reverberation) W2 D1 W1 Classical room acoustics (late reverberation) Solutions: W3 Number of devices Location on walls Sound Power Level 2010 NHCA Conference – Orlando, Florida February 25-27, 2010 D3 D2 Validation Workshop Area (8.77m 14.75m 6.62m) in Building M-37 at NRC (Ottawa). Experimental set-up: – 3 workstations (W1-W3) – 2 noise sources (N1-N2) – 2 noise types (continuous, impact) – 3 alarm frequencies (500, 1000, 2000 Hz) – 5 subjects – Open ear + HPD 2010 NHCA Conference – Orlando, Florida February 25-27, 2010 Validation Psychoacoustic validation of “Detectsound”: – Masked THR prediction error (0.0 1.4 dB) – Preferred level for a 3-tone alarm (18.3 dB 3.1 dB above THR) – Detectsound design window (12 to 25 dB above THR). Acoustic validation of “AlarmLocator”: – 3 source positions, 3 workstations, 3 frequency bands (n=27) – Omnidirectional source B&K 4295 (known power level) – Workstation SPL prediction error (0.1 dB 0.9 dB) 2010 NHCA Conference – Orlando, Florida February 25-27, 2010 Simulation Study Goals: 1. Investigate the effects of hearing protectors on the warning sound design window (TLlow, TLup) for individual workers at specific workstations. 2. Investigate warning sound design constraints when workers with different hearing status share a common work area. Interaction of hearing loss and hearing protectors on the perception of warning sounds 2010 NHCA Conference – Orlando, Florida February 25-27, 2010 Simulation Study Work Area: – Reverberation times: 0.9s (250-1000 Hz), 0.8s (2000-4000 Hz) – 3 workstations (W1 = 86 dBA, W2 = 91 dBA, W3 = 96 dBA) – Low-frequency noise (upper spread of masking) Level (dB SPL) Noise Y X W1 90 W3 80 70 60 31.5 W2 63 125 250 500 1000 2000 4000 8000 Frequency (Hz) 2010 NHCA Conference – Orlando, Florida February 25-27, 2010 14.75 m 8.77 m 100 Simulation Study Workers (Hearing Status): Indiv1 (mild HL): Indiv2 (moderate HL): Indiv3 (mod. severe HL): 0 Male 40 yr (20 yr @ W1= 86 dBA) Male 50 yr (30 yr @ W2= 91 dBA) Male 55 yr (35 yr @ W3= 96 dBA) HEARING THRESHOLDS 10 20 30 40 50 60 70 80 500 0 Broadening factor Hearing Level (dB HL) – – – 1000 2000 3000 4000 6000 FREQUENCY SELECTIVITY 1 2 3 4 5 500 Frequency (Hz) 2010 NHCA Conference – Orlando, Florida February 25-27, 2010 1000 2000 3000 Frequency (Hz) 4000 Simulation Study Hearing Protectors (CSA Z94.2-02; EN 458-2005): Selection: MINIMUM ATTENUATION Protected levels: Overprotection: Acceptable: Optimal: Acceptable: < 70 dBA 70 75 dBA 75 80 dBA 80 85 dBA Insufficient: > 85 dBA 0 Attenuation (dB) Class C: Leq ≤ 90 dBA Class B: 90 < Leq ≤ 95 dBA Class A: 95 < Leq < 105 dBA 5 10 C 15 20 B 25 30 35 125 A 250 2010 NHCA Conference – Orlando, Florida February 25-27, 2010 500 1k 2k 3k Frequency (Hz) 4k 6.3k 8k Simulation Study Common design window for 3 workers at W1 (86 dBA) Common design window for 3 workers at W3 (96 dBA) 110 110 Poste W3 3 Poste W 1 100 100 Niveau SPL) Level (dB dB SPL) Level dB Niveau (dBSPL) SPL) 1 90 80 70 90 80 70 Class C 60 125 Class A 60 200 315 500 800 1250 2000 3150 125 Fréquence Frequency(Hz) (Hz) At high frequencies, warning sounds cannot simultaneously meet requirements for Indiv1 and Indiv3. No design window above 2500 Hz. 200 315 500 800 1250 2000 3150 Fréquence Frequency(Hz) (Hz) Design window limited by 105 dB SPL maximum at low frequencies and by the conflicting requirements for Indiv1 and Indiv3 at high frequencies. 2010 NHCA Conference – Orlando, Florida February 25-27, 2010 Simulation Study Installation of warning devices: – Meet common design windows at the 3 workstations – Four warning signal components (500, 600, 1000, 1600 Hz) – AlarmLocator (ND = 1) D1 X (m) Y (m) Z (m) Sound Power Level Lw (dB) 14.8 5.0 3.0 500 Hz: 116 600 Hz: 114 1000 Hz: 114 1600 Hz: 110 X W1 W3 D1 W2 14.75 m 2010 NHCA Conference – Orlando, Florida February 25-27, 2010 8.77 m Y Simulation Study Results: – Warning sound design window is fairly insensitive to attenuation of hearing protectors for workers with normal hearing or mild hearing loss. – Design window is highly sensitive to attenuation achieved at high frequencies (>2000 Hz) for workers with moderate or greater hearing losses. Accurate warning sound solutions require accurate estimates of field attenuation. – Design of warning sounds in a workplace can become a challenge when workers with different hearing status share a common work area. – Warning sounds in the frequency range from 500 to 1600 Hz is recommended (in agreement with ISO 7731). 2010 NHCA Conference – Orlando, Florida February 25-27, 2010 Conclusions Detectsound provides valid estimates of the optimal design window for warning sounds based on a psychoacoustical analysis of the relevant parameters at each workstation. AlarmLocator provides possible solutions for the number and placement of warning devices based on a simulation of the sound propagation in the work area. In general, warning sound frequency components in the range 500-1600 Hz are recommended for workers with hearing loss or wearing hearing protectors (ISO 7731). Care must be taken not to overgeneralize recommendations to special situations, such as high-frequency noise environments, low-frequency hearing loss or unusual attenuation profiles. 2010 NHCA Conference – Orlando, Florida February 25-27, 2010