By:

Sepideh Abolghasem 81101205

Shabnam Alaghehband 81124000

Mina Khorram 81128618

May 2006

• Introduction to Noise

• Noise Effects

• Noise Reduction Benefits

• Noise Reduction Methods

• Some Examples

• Sound versus Noise

Noise is an unwanted sound.

• Its intensity is measured in decibels (dB)

The decibel scale is logarithmic.

• Human can hear sounds between 30-20000 Hz

Typical Noises Corresponding to dBA Values

Source Noise LevelNormal threshold of hearing 15 Whisper 30Quiet park 45

Normal conversation 60Noisy office 75Noisy factory 90

Dog bark 95Car horn 100Jackhammer 105Jet takeoff 130

Factors that can affect how hazardous noise is:

• Intensity• Time duration• Time distribution• Frequency

Sound Pressure

Level (dBA)

83 85 87 90 92 95 97 100 102 105 108 110

Reference duration (hours)

21.1 16 12.1 8 6.1 4 3 2 1.5 1 .66 .5

1. Hearing Loss• Risk of damage starts at 85 dB or higher

• Longer exposure time increase your risk

• Excessive noise damages the hair cells in the cochlea

• Noise makes your ears ring all the time

Effective Noise Level(db)

Rec

omm

end

ed M

axim

um

Du

rati

on(h

r)

Percentage of hearing loss due to intensity

and duration of exposure :

Intensity(dB) After 10 years work(8 hours a

day)

After 35 years work(8 hours a

day)

80 0% 0%

85 3% 9%

90 10% 20%

95 17% 32%

100 29% 44%

105 42% 51%

2. Annoyance and Distraction

• Noise from office or production equipment can reduce the effectiveness of communication and make it difficult for people to concentrate in some tasks.

• A handful of research studies confirm that noise has a negative effect on a child's ability to learn.

Preferred Noise Criterion (PNC) Curves

• The Preferred Noise Criterion (PNC) curves provide guidelines for ambient sound pressure levels.

• The higher the frequency of the noise, the lower its intensity must be to bring it to the appropriate PNC curve for hearing or communication.

Frequencies (Hz)

Pre

ssu

re L

evel

(dB

)

Evaluation Of Pump Noise In a Forman’s Office

3. Interference with Communication

• Speech interference by noise is common around machinery and business equipment.

• The most common method for rating the speech interference effects of noise is called the Preferred Speech Interference Level (PSIL).

Curves are drawn to estimate the distance at which intelligible communication can be made at different levels of PSIL.

The ability to hear and converse effectively on the telephone is also important and can be predicted by PSIL measurement.

The following guideline for calls between telephone exchanges should be used :

PSIL Telephone Use60 dB or less

60 to 75 dB

Above 75 dB

Satisfactory

Difficult

Impossible

4. Performance Effects Of Noise

The following general observation apply to situation where noise may affect performance:

• Paced tasks

• Information transfer

• Noise features

5. Physiological effects :

• The hazardous effects of noise does not limit to hearing loss but also includes the other parts of your body.

• The exposure to noise has an effect that results in having more adrenaline in blood and causes stress.

• Disturbing sleep.• Extreme exhaustation.• ….

6. Increased risk of accidentsNoise need not be excessively loud to cause

problem in the workplace. Noise can interact risks to workers by :

• Increasing the risk of accidents by masking warning signals;

• Being a casual factor in work-related stress.

Music

In some factories background music has been used to improve the environment.

• Do not provide music if the background noise level is more than 70 dB.

• It can be use for repetitive tasks.• In offices the white noise served to mask some

of the speech sound from neighboring areas.• White noise levels of 48 dB can be effective, but

levels above 52 dB may be distracting and annoying.

Evacuation AlarmsEvacuation alarms notify people in a

work area of a situation requiring them to leave the building.

• It should precede any sounds around.

• It should have a minimum duration of 10 s.

• Alarms should be repeated until the building is evacuated.

• Also for people with hearing loss we should consider visual alarms.

Noise Reduction Benefits

Workplace noise is a major occupational health problem resulting in thousands of disability claims per year.

Potential benefits of workplace noise reduction:• improved safety and productivity• reduced hearing loss• better communication• warning sounds heard more reliably

Noise Reduction Methods

Noise reduction methods can be applied at the noise source, in the path of noise transmission. Methods of reduction involve the following techniques:

• Reducing the level or altering spectrum of the generated noise.

• Using barriers to reduce noise transmission through air or structures.

• Absorbing incident or reflected noise.

Engineering Controls

• Keep doors shut (reduces noise by 10-20 dB).• Take care of mufflers and other controls.• Damping.

Then: Protect your ears• Find comfortable hearing protection (ear

plug, canal cab, ear muff)

• Learn to wear them correctly.

• Don’t go into noise without it!

Acoustical Noise Reduction Blankets Advantages• can be installed with plant personnel • can be removed and reused numerous

times • is a closed insulation system • is custom-fit to existing conditions • is vibration resistant

Applications• any load manufacturing process • gear box casings • steam and gas turbine housings • compressor housings • pressure reducing valves • liquid chillers

Noise Control In Child Development Center

Wall system at the kiwi Grille

Quieting a computer server roomNowadays, every company has to have a computer server room. These rooms are host to lots of computers and servers that all require fans to keep their systems cooled. All of these fans running at one time create excessive ambient noise.