Hearing Conservation and Noise Measuring Equip..ppt

Noise Measurement,Training Module,© 3M 2013. All Rights Reserved.,Table of Contents,Physics of Sound (Hearing loss, terminology)OSHA (Regulations)Sound Level MetersNoise Dosimetry,© 3M 2013. All Rights Reserved.,Noise Measurement and Dosimetry Learning Objectives,Explain sound pressure level, frequency & respective units of measureDescribe level average, time weighted average & doseExplanation of criterion, threshold & exchange rateProper placement & care of microphones and instrumentationExplain hearing conservation regulations & OSHA requirements as it pertains to noise measurementHands on calibration, function & measurement with the noise dosimeter, sound level meter and octave band analyzers,Section IPhysics ofSound,1-20,,,,Sound vs Noise?,© 2009 3M Company. All Rights Reserved.,Why Measure Noise?,I. Determine if the employee(s) are at risk for Noise Induced Hearing Loss (NIHL) & should be in a Hearing Conservation Program (HCP)Differentiate between on-the-job & off-the-job noise exposureDetermine most effective hearing protectionEngineering ControlsAdministrative ControlsCompliance with applicable Standards,Why Measure Noise?,Prolonged exposure to noise causes permanent and debilitating hearing lossMostly between 4 – 8 kHzLose ability to understand speech in many situationsTypically affects consonant receptionIndividual losing hearing is often the last to know!,Why Measure Noise?,Long term health effects due to adrenaline releaseMore accidents in high noise environmentsMeasurable decrease in productivityMeasurable decrease in work accuracyIncreased fatigue,Noise Induced Hearing Loss,Intensity + DurationDamage occurs in the cochleaResults in loss of comprehension, not loudnessPermanent,,Definition of Sound,Fig. I-3 Compression & Rarefaction of air molecules,What does Sound look like?,Adapted from Acoustics Animations – Dr. Dan Russell – Kettering University Applied Physics http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html,Compression & Rarefaction ofAir Particles in a Sine Wave,Four Characteristics Of Sound,Frequency (measured in Hz)Intensity (measured in dB)Speed (measured in feet or meters/second)Wavelength (measured in feet or meters),Frequency,Measured in Hertz (Hz)kHz for 1000xHzRelates to the pitch of the signalIs a measure of the cycles completed in one second,Frequency – (Pitch),Fig. I-4 1Hz and 10Hz Sine Waves,Typical Frequency Examples,Lathe 50 to 1100 HzCompressed air 500 to 8000 HzCircular saw 300 to 12000 HzCars 8 to 1100 HzViolin 300 to 9000 Hz,Frequency Response & Weighting,The human ear is capable of responding to frequencies ranging from 20 Hz to 20 kHz The ear is less efficient at high and low frequenciesIn the range from 500 Hz to 4 kHz a normal human ear is very sensitive,Frequency Response & Weighting,Fig. I-6 “A” and “C” Weighting Curves,Sound Pressure Level,Fig. I-7 Sine Waves with different sound pressures Measured in decibels (dB),2 Sine Waves: Same FrequencySame Time DurationDifferent IntensityOne is TWICE as loud as the other,Understanding deciBels (dB),deciBels S P LdB SPLSoundPressureLevelRelates to measurements of the environment,deciBels H LdB HLHearingLevelRelates to intensity of audiometric test tones,Doubling Sound Source,Add 3 dB10 dB  perceived as “twice” as loud,Addition of Decibels,If the difference between two levels to be added is:- 0 to 1 dB, then add 3 dB to the higher number- 2 to 3 dB, then add 2 dB to the higher number- 4 to 7 dB, then add 1 dB to the higher number- 8 dB or more, then add 0 dB to the higher number,Decibels are logrithmic valuesThey can not be directly added or subtracted,Changing Distance From Source,OutsideDoubling distanceDecrease SPL 6 dBRoomVery Near SourceTwice the distance decreases SPL by 6dBFar from sourceNo change with change in distance,NOTE: These are general guidelines. Each case may vary.,Octaves,Focus on the frequency content of the overall noise signalImportant for noise control efforts,Fig. I-11 Octave Bands,Occupational Noise Characteristics,In the real world of occupational noise the overall sound is a mixture of many simultaneous sources with a variety of frequencies and intensities.,Fig. I-12 Mixture of Source Signals,Types or Characteristics of Sound“Measure all continuous, variable and impact/impulse sound”,A fan is an example ofa continuous noise source,An explosion orgunshot are examplesof an impulsive noise,A hammer striking a nailwould create an impactnoise signal,A forklift driver is anexample of a variableexposure,Response Time,Slow 1 second rise and fallFast 0.125 second rise and fallImpulse 35 millisecond rise 1.5 second fallPeak 50 microsecond rise and fall,Various time responses,,,,,,,,Peak,Max,,Types of Hearing Protectors,MuffsPlugs Foam formable Pre formed CustomOthers Plugs on a head band Noise cancellation,。