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Noise at Work Definitions • Leq: Fluctuating instantaneous noise level is averaged over a period of time. Similar to TWA. • Lepd: Daily personal noise exposure.8 hour equivalent continuous sound level. • Loudness: The ears subjective judgement of sound intensity level. Frequency is an important factor. • Octave Band Analysis: Used to measure the composition of noise pressure levels and frequencies. dB • Given in logarithmic form • +3dB = doubling sound intensity so 93dB(A) for 4 hours is in fact equivalent to 90dB(A) Lepd • Our response to sound intensity differs with frequency, so the “A” weighted scale on sound level meters accounts for this, hence “dB(A)” Problems Associated with Noise Exposure • • • • • • Tinnitus Noise Induced Hearing Loss Acoustic Shock Temporary or permanent threshold shift Interfere with communication Stress Noise Measurement • Simple sound level meters can be used when noise level is fairly constant. • Noise dosimeters measure Lepd where workers are exposed to complex and variable noise fields Preventive Measures • Damping (stiffening rods, double skinning etc.) • Absorption (absorbent materials) • Isolation (acoustic havens) • Enclosure (remember maintenance access) • Reduced time exposure • Ear protection Types of Ear Protection • Disposable earplugs – Useful for temporary use e.g. visitors, maintenance work, supervisors etc. – Useful where employee turnover is high, whilst ear muffs are being obtained • Re-usable earplugs • Earmuffs (Ear Defenders) Earplugs Advantages • • • • • Universal fit Cheap Low maintenance Easily worn by spectacle wearers Good user acceptance Earplugs Disadvantages • Low attenuation at speech frequencies • Difficult to observe whether being worn • Cannot be used where process involves possibility of contamination e.g. food • Does not reduce sound intensity transmitted through bone structure around the ear Earmuffs Advantages • Provide the best attenuation across the aural frequency spectrum • Reduce transmission of sound intensity via auditory canal and bones around ear • Use is easily supervised • Can be used where possibility of process contamination exists e.g. food manufacure Earmuffs Disadvantages • Expensive • Cumbersome – poor user acceptability • Have to adapt to use with head protection or RPE • Don’t go well with long hair or glasses • Require planning & resources to maintain • Communication can be impaired Control Strategy