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Casella CEL Noise Book

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Casella CEL Noise Book NNooiissee!! AAnn IInnttrroodduuccttiioonn ttoo IInndduussttrriiaall NNooiissee MMeeaassuurreemmeennttss aanndd HHeeaarriinngg IIssssuueess iinn tthhee WWoorrkkppllaaccee Contents Introduction.................................................................................................................5 Physical properties of sound ..............................................6 The decibel (dB) Scale.......................................................................8 The ‘A’ weighting scale ................................................................11 Figure 1. Equal loudness curves after Fletcher and Munson .................................................................11 Figure 2. The ‘A’ frequency weighting curve used in sound level meters.............................................13 Figure 3. Addition of identical noise sources. .......................................................................................16 Figure 4. The ‘C’ frequency weighting curve used in sound level meters.............................................18 The hearing process ..............................................................................19 Figure 5. Simplified anatomical diagram of the ear...............................................................................20 Hearing problems .......................................................................................22 Occupational deafness ....................................................................24 Noise induced stress..............................................................................26 Damage risk criteria ............................................................................27 Figure 6. Noise and exposure duration (Noise Dose) Relationship.......................................................27 CASELLA CEL USA page 2 of 84 INTRODUCTION TO NOISE last updated February 2010 www.CasellaUSA.com Dealing with the real world ............................................... 32 Figure 7. Typical time history variation of industrial noise levels........................................................ 32 Hearing conservation programme..................... 36 Noise measurements............................................................................. 38 Figure 8a. Steady or stepwise noise climate ......................................................................................... 39 Figure 8b. Noise climate with impulses present.................................................................................... 39 Figure 8c. Completely variable noise climate....................................................................................... 40 Figure 9. The CEL-254 Simple sound level meter for spot checks....................................................... 41 Figure 10. Free and random sound fields.............................................................................................. 42 Figure 11. The CEL-320S Integrating Convertible sound level meter.................................................. 44 Measurement of impulsive noise............................. 46 Figure 12. The CEL-440 Integrating octave band sound level meter ................................................... 47 Figure 13. The CEL-360 Logging personal noise dosimeter ................................................................ 48 Figure 14. The CEL-480 Logging Sound level meter........................................................................... 49 Figure 15. Time history intervals from a data logging noise dosimeter................................................ 51 Noise control & ear protectors .................................. 54 Figure 16. Collecting octave band data around a machine.................................................................... 54 Table 1. Typical manufacturer’s data for a hearing protector............................................................... 57 Figure 17. Typical industrial noise spectra from two different sources ................................................ 58 Table 2. Effect of removing a hearing protection device for part of the workday ................................ 61 Types of hearing protector & their use... 62 Figure 18. Typical earplugs fitted into the ear canal............................................................................. 62 Figure 19. Typical circumaural ear muffs to fit around the outer ear.................................................... 63 Audiometric testing................................................................................. 65 Figure 20. Testing a subject’s hearing threshold levels in an audiometric booth.................................. 66 CASELLA CEL USA INTRODUCTION TO NOISE page 3 of 84 www.CasellaUSA.com last updated February 2010 Figure 21. A typical audiometric chart showing the hearing loss of a carpenter ...................................67 Glossary of terms...............................................................................................69 Appendices ...................................................................................................................75 Appendix A ................................................................................................................................................75 Sound levels and reference duration for equivalent noise dose .............................................................75 Appendix B ................................................................................................................................................78 Conversion from 8 hour Projected Noise Dose % to 8 hour TWA and LEP,d equivalent continuous sound levels ...........................................................................................................................................78 Appendix C................................................................................................................................................81 Addition and subtraction of decibels.....................................................................................................81 Other Information .....................................................................................................................................83 CASELLA CEL USA page 4 of 84 INTRODUCTION TO NOISE last updated February 2010 www.CasellaUSA.com Introduction This booklet is about the protection of employees and visitors from the effects of excessive noise in the workplace. Occupational noise can and does damage our hearing, resulting in serious social and physical handicap. The prime objective of an industrial noise control programme is to protect employees from suffering permanent hearing loss due to high noise exposure. We have all probably experienced a temporary hearing loss following noise exposure at a loud disco, from hammer drilling of concrete for an extended period, shooting etc. However, our hearing soon returns to its normal state, with the time taken to recover depending on the exposure severity. This recovery appears to be total. However, repeated exposure to high levels will lead to a permanent hearing loss. Consequently, limits for occupational noise exposure have been established that are designed to protect the majority of the workforce against noise-induced deafness. As is so often the case, there is a relationship between the degree of protection and the costs of compliance. Current limits protect the vast majority of the workforce but not everyone will be equally protected due to differing human susceptibility to noise induced- deafness. Like most human senses we judge sound in a subjective manner and so it makes quantitative assessments very difficult. Hence the correct measurement and analysis of the level is critical in deciding the degree of hazard that is present and what type of noise control measures are required for a particular situation. Modern sound level meters and noise analysers or dosimeters have facilitated the accurate measurement of the noise levels provided that the instruments are properly used, calibrated and regularly re-certified. These measurements provide the basic data upon which the degree of hazard may be decided and the correct remedial measures prescribed. CASELLA CEL USA INTRODUCTION TO NOISE page 5 of 84 www.CasellaUSA.com last updated February 2010 Physical properties of sound The passage of acoustic energy through air results in the instantaneous pressure at any point in space and time consisting of two components; namely the atmospheric pressure and the sound pressure. The atmospheric pressure only changes slowly as weather systems come and go with the standard atmospheric pressure (STP) at mean sea level and 20 Celsius (68 Fahrenheit) being 101,325 kiloPascals (29.9 in mercury, 1013 mbar). The symbol kPa is usually used for the air pressure and this unit replaces N/m-2 with which it is identical. Audible pressure fluctuations are a result of the passage of acoustical energy through the air and are normally much less than 1 Pa; they are tiny in comparison with atmospheric pressure. These tiny fluctuations are extremely important to our lives. An acoustic wave can therefore be quantified in terms of the amplitude and frequency of these pressure fluctuations. Even the most complex sound can be analysed into individual components at different specific frequencies and levels. Generally speaking frequency is interpreted as pitch and the amplitude of the pressure fluctuations as loudness. However, these two parameters are interdependent,
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