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