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حفاظت کاهندگی واقعی nrr شنوایی تعیین

تعیین کاهندگی واقعی حفاظت شنوایی NRR
#1
توضیح اینکه اگر بر روی کاتالوگ ایرپلاگ شما نوشته 30=NRR دسی‌بل، مقدار 30 دسی‌بل فقط به معنای کاهندگی اسمی ایرپلاگ بوده و بایستی کاهندگی واقعی آن با تست فنی توسط یونیت‌های مخصوص تعیین گردیده و یا توسط فرمول به طور تقریبی محاسبه گردد که فرمول آن (ارائه شده توسط NIOSH) به شکل ذیل می‌باشد:
NRR-7)×50%)
بعد از جایگذاری متوجه می‌شویم که NRR از 30 به 11.5 کاهش می‌یابد که مقدار ۱۱/۵ در واقع NRR عملیاتی یا واقعی می‌باشد. و نکته آخری که در عکس نوشته موجود است این است که در استفاده همزمان ایرپلاگ و ایرماف 5 دسی‌بل به مقدار واقعی NRR افزوده می‌گردد
11.5+5=16.5
فرمول محاسباتی NRR ایرماف و ایر پلاگ با روش niosh و osha
OSHA Method
A-weighted measurements: Lprot = L - (NRR - 7) / 2
C-weighted measurements: Lprot = L - NRR / 2
NIOSH Method
(A-weighted measurements: Lprot = L - (NRR - 7
C-weighted measurements
(Foam Earplugs: Lprot = L - (NRR * 0.5
(Other Earplugs: Lprot = L - (NRR * 0.3
(Earmuffs: Lprot = L - (NRR * 0.75
Where
Lis the measured sound level or TWA
NRR is the Noise Reduction Rating provided by the hearing protector manufacturer
Lprot is the estimated sound level at the ear when wearing the hearing protection

نویسنده: هادی بیات مهندسی بهداشت حرفه ای

   APPENDIX E--NOISE REDUCTION RATING   Updated: August 15, 2013
(This appendix will be replaced when the new NRR scheme is promulgated)
Noise Reduction Ratings
When OSHA promulgated its Hearing Conservation Amendment in 1983, it incorporated the EPA labeling requirements for hearing protectors (40 CFR 211), which required manufacturers to identify the noise reduction capability of all hearing protectors on the hearing protector package. This measure is referred to as the noise reduction rating (NRR). It is a laboratory-derived numerical estimate of the attenuation achieved by the protector. It became evident that the amount of protection users were receiving in the workplace with the prescribed hearing protectors did not correlate with the attenuation indicated by the NRR. OSHA acknowledged that in most cases, this number overstated the protection afforded to workers and required the application for certain circumstances of a safety factor of 50# to the NRR, above and beyond the 7 dB subtraction called for when using A-weighted measurements. For example, consider a worker who is exposed to 98 dBA for 8 hours and whose hearing protectors have an NRR of 25 dB. We can estimate the worker’s resultant exposure using the 50# safety factor. The worker’s resultant exposure is 89 dBA in this case
The 50# safety factor adjusts labeled NRR values for workplace conditions and is used when considering whether engineering controls are to be implemented
Estimated dBA exposure = 98 dBA - [(25-7) × 50#] = 89 dBA
However, when assessing the adequacy of the hearing protection for hearing conservation (HC) purposes, CSHOs should only subtract 7dB from the NRR
Exposure for PPE/ HC enforcement = 98 dBA - (25-7) = 80 dBA
Single/Double Hearing Protection
Dual hearing protection involves wearing two forms of hearing protection simultaneously (e.g. earplugs and ear muffs). The noise exposure for workers wearing dual protection may be estimated by the following method: Determine the hearing protector with the higher rated NRR (NRRh) and subtract 7 dB if using A-weighted sound level data. Add 5 dB to this field-adjusted NRR to account for the use of the second hearing protector. Subtract the remainder from the TWA. It is important to note that using such double protection will add only 5 dB of attenuation. For an example of a calculation of dual hearing protection, see Methods for Estimating HPD Attenuation of the OSHA Noise Safety and Health Topics Page
For a more extensive discussion of how to use the NRR, see the NIOSH website. NIOSH has developed guidelines for calculating and using the NRR in various circumstances. (Hearing Protector Devices

نویسنده: دبیر انجمن
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