*HEARING

PROTECTION

DEVICES

Earplugs.Pre-formed

Single Flange Triple Flange Quad Flange Combat Arms Ear Plugs

.Hand-formed Noise Muffs Ear Canal Caps Helmets

*Approved Types of HPD’s:

Single Flange (No longer manufactured): Noise Reduction

Rating (NRR)=23dB 5 color-coded sizes:

White (Extra Small) Green (Small) Orange (Medium) Blue (Large) Red (Extra Large)

*Pre-Formed (Vinyl) Earplugs

*Pre-Formed Earplugs (cont.):

*Triple Flange:NRR= 26dB3 color coded sizes:Green (Small)Orange (Medium)Blue (Large)

*Pre-Formed Earplugs (cont.):

Quad Flange:NRR= 25dB

*Hand Formed Foam Earplugs

*NRR=19-28dB, depending on fit characteristics.

*Ear Canal Caps:*Noise Reduction Rating

(NRR)=18dBNRR is extremely variable with this HPD

*Circumaural Noise Muffs*Noise Reduction Rating (NRR)=25dB

Only approved protection is acceptable

Selection should be based on Advantages/disadvantages Work environment Attenuation NRR

*HPD Selection Considerations:

*NRR ?

* The NRR describes:

the average sound level

reduction (attenuation)

provided by a hearing protection

device (HPD) in a laboratory

test.

*Manufacturers of HPDs

are required by the

Environmental Protection Agency to

have various products tested in order

to obtain an NRR prior to placing

them on the market.

*Actual noise reduction achieved

under field conditions using any

HPD will be much lower than the

assigned NRR.

Adjustment

of the assigned NRR may need to be

made before a device is prescribed for

field use.

A. WEIGHTING-SCALE ADJUSTMENT

.If workplace noise levels are determined by

using the A scale (dBA) on the

monitoring instrumentation, the assigned

NRR must be reduced by 7 dB before being

subtracted from the actual measured TWA

noise levels to determine the legal "adequacy"

of the device

B. DERATING

OSHA

derates NRR (after weighting-scale

adjustment) by one-half (50%)

for all types of HPDs to determine the

"relative performance".

NIOSH

recommends a variable scheme for derating

For example,

Earmuffs are derated 25%

formable earplugs are derated 50%

all other earplugs are derated 70%

B. DERATING ( cont.)

*THESE RESULT IN:

“Predicted field attenuation”or“relative performance”ofthe device.

C. COMBINING HPDS

-The NRRs of the combined devices are not added together to determine the total noise reduction.

-OSHA advises that 5 dB is to be added after thweighting-

scale adjustment is applied to the device with the higher

NRR (but does not require the 50% derating described earlier.)

As a practical matter ,

Double protection is inadequate

When

TWA noise exposures exceed 105 dBA.

*

An Example of Reducing the NRR

8-hour TWA noise exposure: 93 dBA

NRR of hearing protectors: 29 dB

*1.Subtract 7 dB from the NRR: 29 dB - 7 dB = 22 dB2.Divide by 2: 22 ÷ 2 = 11 dB3.Subtract 11 dB from the8-hour TWA noise exposure: 93 dB - 11 dB = 82 dB

4.Decide if 82 dB ( “Protected Exposure”)is below the PEL for noise