Water Well Journal
Issue link: https://read.dmtmag.com/i/715953
• Be compatible with other PPE • Be replaced when deteriorated. There are a variety of styles of hearing protectors and each provides different levels of protection. Earplugs are available as foam, pre-molded, and custom molded earplugs. Hearing protectors are also available as earmuffs. Consider also wearing canal caps—they resemble earplugs on a flexible plastic or metal band which have flexible tips that plug the ear canal. They don't extend into the ear canal, they just close the ear opening. Canal caps are ideal for those situations where hearing protection has to be taken on and off frequently. How to Measure Hearing Protection The most common way to evaluate hearing protection is the noise reduction rating (NRR). Most manufacturers of hearing protection devices indicate the NRR for their product on the packaging—since the U.S. Environmental Protection Agency requires it. Appendix B of the Occupational Safety and Health Admin- istration's occupational noise standard (29 CFR 1910.95) re- quires that 7 decibels (dB) be subtracted from the NRR when using A-weighted sound levels. A-weighting is applied to instrument-measured sound lev- els to account for the relative loudness perceived by the human ear and commonly used for the measurement of envi- ronmental and industrial noise. A-weighted measurements are expressed as dBA or dB(A). Scientific literature indicates laboratory-based noise reduc- tion data for hearing protectors are seldom achieved in the workplace. As a result, applying an additional safety factor of 50% is recommended to adjust for workplace conditions. The National Institute for Occupational Safety and Health's recommendations for de-rating the NRR are different than OSHA's protocols. For earmuffs and formable earplugs, NIOSH recommends 25% and 50% be subtracted, respec- tively, from the labeled NRR. For other earplugs, NIOSH recommends 70% of the manufacturer's labeled NRR be subtracted. Wearing dual hearing protection (both earmuffs and earplugs in combination) does not equate to additive protec- tion. Decibels cannot be added together like other numbers. Likewise, the NRRs of both the earmuffs and earplugs cannot be added together. SAFETY continues on page 50 Table 1. Common Noise Sources and Possible Solutions Source Noise Emissions Possible Solutions Electric motors Air turbulence around intake Air turbulence can be controlled by installing an for cooling fan. air intake silencer or by changing out the motor Mechanical vibration fan blade to a more aerodynamic blade type. of support structure. Mounting the motor on isolation pads or mounts can control mechanical vibration. Compressed air Turbulence due to mixing of gases Reducing the velocity of air to as low as possible with different velocities. can control air turbulence. Silencers should be Turbulence caused by air installed on air exhaust points. Dust off nozzles impinging against fixed objects. can be replaced with low-noise types. Air ejection systems may sometimes be replaced with water systems. Pipelines, valves, Transmission of vibration Transmission of vibration can be controlled using and ducts from fixed equipment. vibration-dampening treatments or isolators. Turbulence caused by gas or fluid Mounting piping or ducting on vibration-isolating passing through the pipe or duct. hangers is another option. Noise from turbulent flow can be controlled using pipe lagging. Equipment Vibration transmitted Housing vibration can be controlled by housings by equipment. vibration-dampening surface treatments. Ducts or stacks Turbulence caused by gas flow. Duct or stack noise can be controlled by using Transmission of vibration noise cancellation technology whereby a sound from stack fans. wave opposite to the offending noise is introduced, resulting in a cancellation of the offensive noise. Discrete pieces Mechanical vibration Noise sources can be controlled through low-noise of equipment and resonance. purchasing specifications, proper maintenance, and if necessary, placing the equipment in an enclosure or behind a barrier. WWJ September 2016 49 Twitter @WaterWellJournl