B6-NOISE AND VIBRATION Flashcards
What is noise?
Any audible sound
Explain the terms ‘amplitude’ and ‘frequency’ as applied to a noise wave.
- The amplitude is the maximum displacement of sound wave pressure.
- The frequency is the number of cycles per second that pass a given location
Explain the term pitch?
Pitch is the way the brain interprets the frequency of sound; shrill or piercing sound is high-pitched and associated with high frequencies. Rumble or drones are low pitched sound and associated with low frequencies.
What is the A-weighted scale and what is its purpose?
The A-weighed scale on a sound level meter electronically assimilates the sound pressure and mimics the human ears response across the range of frequencies. The measurements of noise in dB (A) is a good indication of the physical harm cause to hearing.
Why can’t decibel values be added together directly?
Because sound intensity levels are given on a logarithmic form.
Describe how the ear converts sound waves into nerve stimulation to the auditory centres of the brain.
The ear transmits nerve impulses to the brain as a result of detecting and transmitting mechanical vibration through the outer ear, the middle ear and the inner ear.
Explain how the damaging effects of noise are related to the dose that the ear receives.
The dose of the noise the ear receives depends on the level of noise and the duration of exposure. Short exposure to a high level of noise is considered to cause comparable hearing damage to a long exposure to a lower level of noise.
Which of the two types of hearing loss-conductive and sensorineural- is more relevant to the health and safety practitioner?
Sensorineural hearing loss (when the hair cells in the cochlea are damaged), in an occupational setting occurs mainly from exposure to excessive noise. Conductive hearing loss (breakdown of the conducting mechanism of the ear from acute acoustic trauma) is a rarer occupational problem.
Explain the term ‘threshold shift’.
A threshold shift is a reduction in a person ability to hear, i.e. they need more sound intensity to stimulate their hearing; the condition may be permanent or temporary.
Identify three factors that can affect the accuracy of audiometric testing.
Technical limitations, learning effect and headphone fit.
What are the main types of equipment available for measuring noise levels and noise exposure.
Simple sound level meters (unlikely to be useful for most noise surveys);
Integrating sound level meters;
Personal sound exposure (dosimeters);
Octave band anaylser (often incorporated into integrating sound level meter).
Outline briefly the requirements of the control of noise at work regulations 2005, regarding assessment of exposure.
Where employers are likely to be
exposed to noise above the lower exposure action value (daily personal noise exposure of 80 dB (A)), the employer must carry out an assessment of exposure to identify people at risk of hearing damage;
The daily noise exposure of those who are likely to be exposed at our above the lower level;
And
Any additional information to comply with the regulations, such as where noise control and hearing protection may be required.
What are the three ways in which a sound wave front may interact with a slab of materials?
Reflection, absorbtion and transmission.
List the three priorities of noise control.
Noise reduction at source;
Attenuation in transmission;
Control at the receiver.
Describe the principles design features of an acoustic enclosure.
Must be airtight;
Mounted so that they do not transmit noise and vibrations to the floor;
Have a heavy noise-reflecting outer skin and a noise-absorbent lining.
Must also have appropriate hatches and doors to allow access to maintenance, etc. May need to be suitably ventilated and lit if eh entry has to be gained by workers. May need windows or vision panels
