Noise Control Practices in the Workplace
STEP Network MeetingAugust 17, 2005
Noise
Before We Discuss Noise Control Let’s Review Some
Noise Concepts
Noise Measurements
Noise Levels are Expressed as Decibels (dB)
DEVICE dBAComputer 37 - 45
Refrigerator 40 - 43
Cloths Dryer 56 – 58
Garbage Disposal 76 - 83
Vacuum Cleaner 84 - 89
Lawn Mower 88 - 94
Weed Whacker 94 - 96
Leaf Blower 95 - 105
Circular Saw 100 - 104
1+1+1 Does Not Equal to 3
The Decibel is a Logarithmic Unit of Measure So We Can’t
Simply Add Numbers
Keep the Calculator in the Desk
We Can Use a Few Rules of Thumb
“Shake, Rattle, and Roll”
How We Perceive Noise
High Frequency Noise
Power Tools, Saws, Grinders Other High RPM Equipment Sudden Release of Pressure
High Frequency Noise
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 Noise
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
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)
6 dB Rule Would Not Apply
6 dB Rule Would Not Apply
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 LoudBe 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
Transmitting Vibration
Noise and Vibration Can Be Transmitted to Other Surfaces
Which Then also Transmits Noise
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 Plugswww.osha.gov