5 Decibel Halving Rule For Each 5 dB Increase in Noise, In order to be Equivalent to the Previous Dose You Must Half the Allowable Exposure Time
Equivalent Dose of 90 dBA Over an 8 Hour TWA Period 95 dBA over 4 Hour TWA Period 100 dBA over 2 Hour TWA Period 105 dBA over 1 Hour TWA Period 110 dBA over ½ Hour TWA Period
Duration (How Long) The 5 dB Rule Can Be Useful in Estimating Whether a Noise or an Activity Would Result in Employees Being Exposed to Noise In Excess of the PEL
Example An Employee Must Enter a Pump Room and Conduct Preventative Maintenance The Small Portable Sound Level Meter Reads 105 dBA Inside the Pump Room How Long Could the Employee Stay in the Pump Room Without Exceeding the Dose Equivalent Noise Exposure of 90 dBA over an 8 hour TWA?
Answer Employee Noise Exposure for 1 Hour at 105 dBA Would Be the Dose Equivalent Exposure of 90 dBA for an 8 Hr TWA.
Administrative Controls Likewise, Limiting Employee Exposure Time to Noise Can Help Reduce the Possibility of Hearing Loss
Watch Where You’re Standing Employee Noise Exposures Often Depend on How Close They Are to the Noise Source
Distance Noise Quickly Decreases as You Move Away from the Noise Source
6 dB Double Distance Rule Noise Will Decrease 6 dB Each Time You Double the Distance (free field, point source only)
Distance From the Noise Source Is It Possible to Move the Employee Workstation or the Noise Source?
If a Tree Falls in the Woods… Moving the Employee or the Noise Source Doesn’t Eliminate the Loud Noise, it Just Reduces the Employee Exposure to it!
Think Out Loud In Moving the Source, Have You Created a Problem for Someone Else?
Isolation Methods Can You Isolate the Noise Source or The Employee From the Noise Source?
Enclosing the Employee The Cab of Heavy Earth Moving Equipment is a Good Example. They are Insulated (and Air Conditioned).
Isolation Methods Install Barriers Between the Employee and Noise Source Enclose the Noise Source Enclose the Employee
Think Out Loud Be Careful When Constructing Barriers or Enclosures. Noise May be Deflected Backwards Off the Barriers or the Walls of the Enclosure Which Can Increase the Noise Intensity on the Noise Source Side. Employees who Must Service Equipment or Conduct Work in Those Areas May Now be Exposed to Greater Noise than Before
Deflection of Sound Waves in Enclosure Creates Louder Noise
Noise Absorbing Material The Good, The Bad, and The Ugly
The Good Noise is Absorbed, It’s Gone, It Wouldn’t Bother Anyone Anymore High Frequency Noises are Easier to Absorb
The Bad Some Types Can be Fragile Some Types Can be Hard to Clean Some Can Be Expensive
The Ugly Some Types Can Be Very Expensive Some Types Won’t Hold Up to Chemicals or Moisture Some Types Can be Combustible
Controlling Noise Generated by Vibration Sources Dampners, Springs, or Isolation Material under Motors and Large Equipment Ensure Plates, Covers, Doors, and Access Panels are Securely Attached Bent or Warped Shafts on Motors and Fans Can Create Vibration Bad Bearings, Flywheels, Pulleys, Fan Blades, and Belts
By the Way Poor Maintenance Can Be a Major Source of Noise Exposure and One Which is Often Consider Economically Feasible.
Noise Created By Escaping Air The Sudden Release of Air Can Be a Significant Source of Noise Exposure
Controlling Noise Created By Released Air Muffler systems on Pneumatic Equipment When Available Reduce Air Pressure if Possible Discourage the Use of Compressed Air for Cleaning Purposes Only Use Approved Nozzles When Compressed Air is Used for Cleaning
You May Not Be The First Person To Ask Contact the Manufacturer of the Equipment and Request Assistance in Determining Ways to Help Decrease Noise Output of the Machines
Hearing Protection Hearing Protection is not a Noise Control Method
Hearing Protection Hearing Protection does not Reduce Employee Noise Exposure, It Reduces the Potential Harm Which Could Otherwise Result in an Unprotected Employee
Hearing Protectors Like Respirators, They are Only Effective if Used Properly
Attenuation of Ear Plugs The Greater the NRR Number the Greater the Protection
Hearing Protectors Ear Plugs and Other Types of Hearing Protection Have Limitations on How Much Protection They Can Provide
Attenuation of Ear Plugs See the OSHA Web Page for Information on Calculating the Attenuation of Ear Plugs www.osha.gov
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