By: Sepideh Abolghasem 81101205 Shabnam Alaghehband 81124000 Mina Khorram 81128618 May 2006
Outline • Introduction to Noise • Noise Effects • Noise Reduction Benefits • Noise Reduction Methods • Some Examples
Introduction to Noise • 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 SourceNoise Level Normal threshold of hearing15 Whisper30 Quiet park 45 Normal conversation60 Noisy office 75 Noisy factory 90 Dog bark95 Car horn 100 Jackhammer 105 Jet takeoff 130
Factors that can affect how hazardous noise is: • Intensity • Time duration • Time distribution • Frequency
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) Recommended Maximum Duration(hr)
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.
Pressure Level(dB) Frequencies (Hz)
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 :
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 accidents Noise 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 Alarms Evacuation 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
Quieting a computer server room Nowadays, 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.