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Noise Control Practices Dr. Wesam Al Madhoun
Noise Before We Discuss Noise Control Let’s Review Some Noise Concepts Noise Measurements • Noise Levels are Expressed as Decibels (dB)
1+1+1 Does Not Equal to 3 The Decibel is a Logarithmic Unit of Measure So We Can’t Simply Add Numbers. “Shake and Roll” • How We Perceive Noise
High Frequency Noise Power Tools, Saws, Grinders Other High RPM Equipment Sudden Release of Pressure • High Frequency Noises Deflect Easier, Are Easier to Shield, Are Easier to Insulate.
Low Frequency Noise Power Presses Pumps, Compressors Other Low RPM Equipment • Low frequency Noises Can Travel Around and Through Objects and Are Harder to Shield and Absorb
Harmful Effects Harmful Effects of Noise Are Related to the Noise Dose Is the Noise Harmful? • Ask Yourself: • How Loud, How Long, How Many Times?
Noise Dose is a Combination Intensity of Noise (how loud) Duration of Noise Exposure (how long) Frequency (how many times during the day are they exposed to such a noise)
Noise Regulated as an 8 hour Time Weighted Average (TWA) An 8 hr TWA of 90 dBA is designated as a Noise Dose of 100%
First Rule of Thumb 5 dB 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? • 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
Noise Absorbing Material 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
Consideration of materials used • Climate • Ease of installation • Durability - resistance to degradation from compression, moisture, decomposition, etc. • Ease of replacement at end of life • Cost effectiveness • Toxicity • Flammability • Environmental impact and sustainability
Transmitting Vibration • Noise and Vibration Can Be Transmitted to Other Surfaces Which Then also Transmits Noise
Controlling Noise Generated by Vibration Sources 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.
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
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 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 • Ear Plugs and Other Types of Hearing Protection Have Limitations on How Much Protection They Can Provide
The techniques employed for noise control can be broadly classified as: • Control at source • Control in the transmission path • Using protective equipment.