Noise Control

Mick Gray

MWG Associates Ltd

The Basics

L= Level, A,C,Z= Weighting F,S,I = Speed The measurement

L A F MX

LAF MX LC pk

LAF MN LA eq (Leq)

L ep’d

Frequency •The rate at which pressure waves

fluctuate

•Measured in Hertz Hz (cps)

–High Hz = high pitch

–Low Hz = low pitch

•Noise usually consists of many

frequencies

•Frequency analysis - used in noise

investigation

Frequency

Frequency

[Hz]

Lowest response of human

ear

20 - 50

Mains hum 50

Middle C 256

BST time signal 1000 (1k)

Most sensitive range of

hearing

1000 – 4000 (1-4k)

Upper range of hearing 10000 - 20000 (10k – 20k)

dB(A)

• Measurements which mimic the

ear’s response to noise

[dB(C) used for peak noise]

A Weighting Corrections Octave Band Centre

Frequency (Hz)

A Weighting

Correction

31.5

63

125

250

500

1,000

2,000

4,000

8,000

16,000

-39.4

-26.2

-16.1

-8.6

-3.2

0

+1.2

+1.0

-1.1

-6.6

A and Linear Frequency Ratings

Lin

A Weighting

Frequency

20

10

0

-10

-20

-30

dB

50Hz 20KHz

C Weighting

Example of the steady noise level

LAEQ = 83 dB

70

80

90

TIME

LA

Below first action level Employer must:

• Reduce risks to lowest practicable level

• Keep records and make them available including

audiometry (if done)

• Buy quiet

1st Action level

First action level:

• 80dB(A) LEP,d

• 112 Pascals (LCPK= 135dB)

• Take action as in regulations

Above first action level

Employer must:

• Identify all employees at risk

• Put up signs

• Review if any changes to noise levels

• Repeat assessment <2 years

• Inform employees of risk

• Provide choice of PPE on request (first aid)

• Provide training / education

• Noise Control

2nd Action level

Second action level:

• 85dB LEP,d

• 140 Pascals (LCPK= 137dB)

• Take action as in regulations

Above second action level

Employer must:

• Demarcate as Noise Hazard Zones

• PPE must be used at all times

• Noise control to reduce exposure

• If Lepd is over 95dBA then must use octave band method to check if hearing protection is effective

Note: For peak action level, take the same action as for second action level

Exposure limit value

• 87dB(A) LEP,d exposure limit

• 140dB LCPK exposure limit (200 Pascals)

• Is the maximum permissible estimated operator noise dose whilst wearing (and not wearing) hearing protection

• Value at the ear after taking into account any PPE

• Therefore necessary to calculate effectiveness of PPE

• NOT a target, but minimum acceptable

• Target these individuals first

Risk Assessment

• Assess risks to Health and Safety

• Done to identify actions to reduce risks

• Necessary when lower action levels likely to

be exceeded

• Should assess exposure, measure if likely to

be above second action levels

Audiometry

• Employees over the second action level have the

right to a hearing check (audiometric test)

• As a preventative measure individuals who may be susceptible to noise below this level should also be tested e.g. those with previous damage.

Hearing Protection

What do we need to

measure for correct hearing protection

• Octave band method

Needs frequency analyser 31.5Hz - 8KHz

• HML Method

Needs C and A weighted LEQ

• SNR Method

Needs C weighted LEQ

Octave band is the preferred method

PNR = M-(H-M) / 4 x (LC - LA - 2)

OR

PNR = M-(H-M) / 8 x (LC - LA - 2)

LAeq Octave’s less

octave attenuation

Lceq - SNR

Octave band method

Octave band centre frequency (Hz) 63 125 250 500 1000 2000 4000 8000 A-weighted

Data on the hearing protector

Mean attenuation (dB) 1 15.3 22.1 32.7 39.3 37.8 43 40

Standard deviation in attenuation (dB)

Measured Noise Levels (dB) 87 98.7 113.5 101.2 103.6 97.2 93.8 84.5 108.6

83 dB

Allow 4dB for 'real-world' factors.

Assume that this device will give:

87 dB at the ear

Colour codes:

Hearing Protection: Peltor Optime III Area/Task: Main Blower Room

Protector does not give adequate protection, or it 'over-protects'

Calculated level at the ear according to

BS EN ISO 4869-2:1995 (=1)

Enter values in all white cells. If the hearing protector data is stated in terms of 'Assumed Protection Values', APV or similar,

then enter the APV values in the 'Mean' row, and leave the 'Standard deviation' row blank or with zeros.

Select a protector so that daily exposure is reduced to at least below 85 dB.

Ideally, aim for between 80 and 75 at the ear. Avoid protectors resulting in

less than 70 dB at the ear - this is 'over-protection' (see BS EN 458:2004).

Protector gives adequate protection, and does not 'over-protect'

Octave band method

Octave band centre frequency (Hz) 63 125 250 500 1000 2000 4000 8000 A-weighted

Data on the hearing protector

Mean attenuation (dB) 1 20 25 31.9 35.2 31.8 38.9 37.8

Standard deviation in attenuation (dB)

Measured Noise Levels (dB) 75 81.8 84.9 85.8 87.7 84.2 78.5 71.4 91.3

59 dB

Allow 4dB for 'real-world' factors.

Assume that this device will give:

63 dB at the ear

Colour codes:

Hearing Protection: PURA FIT 7700 Plugs MOLDEX Area/Task: 60

Protector does not give adequate protection, or it 'over-protects'

Calculated level at the ear according to

BS EN ISO 4869-2:1995 (=1)

Enter values in all white cells. If the hearing protector data is stated in terms of 'Assumed Protection Values', APV or similar,

then enter the APV values in the 'Mean' row, and leave the 'Standard deviation' row blank or with zeros.

Select a protector so that daily exposure is reduced to at least below 85 dB.

Ideally, aim for between 80 and 75 at the ear. Avoid protectors resulting in

less than 70 dB at the ear - this is 'over-protection' (see BS EN 458:2004).

Protector gives adequate protection, and does not 'over-protect'

S.L.M. or Dosimeter?

• Two main types of instrument are used to

perform workplace noise assessments

– Sound Level Meter (SLM)

– Dosimeter

dBadge

• Weighs only 68g

• Measures Personal Exposure

• No cable

• Display & Visual alarms

• 2 Button operation

• Automatic calibration

Lets Make it Quieter

Engineered Noise Reduction

Noise Control

• Source

• Route

• Person – (ear protection)

Noise Control Options

• Options include:

– Don’t use!

– Modify design

– Damping

– Good work practice

– Enclosure

– Screens

– Distance

– Absorption

– Silencers

– Vibration isolation

……etc

Noise Generators

Aerodynamic

•fans •flow induced •pneumatics •nozzles •exhausts •combustion

Noise Generators

Mechanical impacts

presses, stops etc

mechanical handling

rotating machines

gears, pumps,

motors

bearings

electrical forces

friction forces

cutting tools,

brakes

List all the potential noise sources on each

piece of noisy plant Rank the sources Assess all the noise control options for the

dominant source potential reduction in noise from this source operational, productivity, hygiene constraints operator acceptance cost

Noise Control Audit Process

Noise Control Audit Process If engineering control is not practical for

the dominant source, then you have

proved that screening / enclosure etc are

the only options The results are used to generate cost v

noise reduction trade-offs for each item of

noisy plant and to plan the most practical

and cost effective noise control

programme possible across the company.

Noise Control Quiet Nozzles •Entraining Nozzles •c10dB quieter for the same thrust •use c 20% less air than conventional

nozzles •pay for themselves very quickly •intrinsically "safe" (end cannot be

blocked)

Noise Control Probably the single most cost effective noise

control measure that a company can take.

•reduce the chance of importing fresh noise

problems (once on site it

becomes your responsibility to reduce noise

levels to comply with the

legislation).

•generates commercial pressure to develop

quiet plant

•more cost effective to introduce noise control

prior to installation

Noise Control Attitude – new mindset

•Accurate diagnosis and costing of the options

•Simple engineering solutions to common problems

•fans

•pneumatics

•damping

•isolation

Buy Quiet purchasing policy

This approach can produce noise control measures that

actually improve productivity and reduce costs - in

contrast to reliance on conventional enclosures and

acoustic guarding.

Top ten loudest recorded noise’s

Speakers at a Concert = 135 dBA

Firework display = 145 dBA

US Navy Mounted Gun = 150 dBA

Santa Pod Meth / Eth Car = 153 dBA

Space Shuttle Launch = 170 dBA

Krakatoa eruption = 180 dBA

Police AS50 Sniper Rifle = 164 dBA

Blue Whale = 188 dBA

Blue whales mostly emit very loud, highly structured, repetitive low-frequency rumbling sounds that can travel for many miles underwater.. The call of the blue whale reaches levels up to 188 decibels. This extraordinarily loud whistle can be heard for hundreds of miles underwater.

Nuclear Bomb = 198 dBA

Standing as close as 250 feet away from the impact, the resulting explosion from a 1 ton bomb creates a decibel count of 210. Without sufficient hearing protection, not to mention a complete sound-resistant bunker surrounding you, you could quite literally die from the intense vibrations that would literally shake you apart. Unless, of course, you were under the bomb.

USAF Weapon = 210 dBA

A new weapon that is capable of completely dismantling a 3 foot thick concrete wall to powder. If a human body was placed in front of the emitter it would turn the bone structure to a sort of dust like substance. This is not approved as a weapon but is used as an anti weapon

Hoodie Dispersal 25Hz will cause the Brain

to resonate in the skull causing sickness and extreme headaches

Apparently it would be against human rights & we were NOT allowed to do it