Lecture 9 Flashcards
Sound
- is any change in pressure that can be detected (noted)by the ear.
- is any change in waves frequency and/or amplitude (size) that can be detected (noted) by the ear.
- Typically sound is a change in air pressure. However it can also be a change in water pressure or any other pressure sensitive medium.
Noise
unwanted sound
The difference between noise and sound is
in the perception(understanding)of the person hearing it.
(loudly music can be sound for someone and noise for another one)
Sound and vibration
- Sound typically relates to a sensation that is perceived(felt)by the inner ear as hearing.
- Vibration on the other hand is inaudible (unheared) and is perceived(sensed) through the sense of touch.
Pitch (tone, signal) and cycles of sound waves
- Normal atmospheric pressure is represented by a straight line
- Sound is represented by a wavy line that crosses above and below the straight line.
Industrial Noise Types
- Wide band (range)noise: Noise that is distributed over a wide range of frequencies. Most noise from manufacturing machinesis wide band noise.
- Narrow band noise: Noise that is confined (limited) to a narrow range of frequencies. The noise produced by power tools is narrow band noise.
- Impulse noise: Noise consisting of transient pulses (Vibrations)that can occur repetitively or non repetitively. The noise produced by a jackhammeris repetitive impulse noise.
Excessive Noise Physiological (bodily)problems
- The fundamental hazard associated (related)with excessive noise is the loss of hearing (becoming deaf أصم).
- Exposure to excessive noise levels for an extended period can damage the inner ear so that the ability to hear high frequency sound is diminished(minimized)or lost altogether.
- Additional exposure can increase the damage until even lower frequency sounds cannot be heard.
Factors affecting the risk of hearing loss
- Intensity of the noise (pressure level)
- Type of noise (wide band, narrow band, impulse)
- Duration of daily exposure
- Total duration of exposure (number of years)
- Age of the individual
- Coexisting hearing disease
- Nature of the environment in which exposure occurs
- Distance of the individual from the source of noise
- Position of the ears relative to the sound waves
Sound level for personal protection
- The most critical factors causing problems are the sound level, frequency, duration and distribution of noise.
- The unprotected human ear is at risk when exposed to sound levels exceeding115 dB (decibels). youngster in Europe and USA
- Exposure to sound levels below80 dB is generally considered safe.
- Prolonged exposure to noise levels above 80 dB should be minimized through the use of appropriate personal protective devices
- To decrease the risk of hearing loss, exposure to noise should be limited to a maximum 8 hour time weighted average of 85 dB (without protection).
Factors considered by medical professionals in determining causes of hearing loss
The most common measurements are:
- area surveys (study, check, analysis),
- dosimetry, and
- engineering surveys.
Area surveys
•In an area survey, environmental noise levels are measured using a sound level meter to identify work areas where exposures are above hazardous levels.
Dosimetry
•involves the use of body worn instruments (dosimeters) to monitor an employee’s noise exposure over the work shift.
Engineering surveys
typically employ more sophisticated acoustical (sound)equipment in addition to sound level meters. These measurements are used to assess options for applying engineering controls
Noise surveys
involve measuring noise levels at different locations in the workplace
- A sound level meter produces an immediate reading that represents the noise level at a specific instant in time.
- A dosimeter provides a time weighted average over a period of time such as one complete work shift.
Audiometric testing
- measures the hearing threshold (limit, level)of employees.
- For employees found to have a standard threshold shift (hearing decrease), the employer is required to fill out a form in which the loss is recorded as a work time illness.
Follow Up
Follow up is critical.
Failure to take prompt (quick) corrective action at the first sign of hearing loss can lead to permanent weakening damage.
The appropriate follow up activities to initial hearing loss test are the following:
- Testing other employees to determine if the hearing loss is isolated (only) to the employee in question or if other employees have been affected.
- Administering a retest to verify the hearing loss.
- Changing or improving the type of personal protection used.
- Conducting a noise survey in the employer’s work area to determine if engineering controls are sufficient.
Engineering controls
- The steps taken, other than administrative or personnel protection procedures, to reduce the sound level at the source or within the hearing zone of workers.
- All of the engineering controls are designed to reduce noise at:
- the source,
- along its path,
- or at the receiver. (Minimizing the source of noise as much as possible).
Administrative controls
The controls that reduce the exposure of employees to noise rather than reducing the noise.
Administrative controls should be considered a second level approach with engineering controls given top priority.
HAV stands for
Hand Arm Vibration syndrome is the most common vibration related problem.
You can prevent it by:
- Purchase low vibration tools.
- Limit employee exposure to no more than 4 hours per day, two days per week.
- Change employee work habits to safer habits such as wearing properly fitting thick gloves that can partially absorb (take in) vibration,
- taking periodic breaks (at least 10 minutes each hour),
- using a loose grip on the tool and hold it away from the body,
HPD
Hearing protection devices
Hearing protection devices are
- Enclosures devices: Devices that completely cover the employees head, much like helmets.
- Earplugs devices (aural devices): Devices that fit into the ear canal.
- Superauralcaps devices: Devices that fit over the external edge of the ear canal and are held in place by a headband.
- Earmuffs devices: Devices that cover the entire ear with a cushioned cup that is attached to a headband
Earplugs and earmuffsare able to
reduce noise by 20 to 30 dB
By combining earplugs and earmuffs an additional 3 to 5 dB of blockage can be gained.
Evaluation of a hearing loss prevention program
- Hearing loss prevention programs should be evaluated periodically to ensure their effectiveness.
- Such evaluations should have at least the following components:
- training and education:
- trainingat least once a year, provided by qualified instructor,
- evaluation of training, content revised periodically,
- manager and supervisor involvement
- supervisors provided with knowledge,
- wear hearing protectors in appropriate areas,
- posters,
- handouts,
- personal counseling (advising)sessions.
- Discipline (correction, e.g. punish) employees who repeatedly refuse to wear hearing protectors.
Evaluation of a hearing loss prevention program
engineering and administrative controls
most effective means of controlling or eliminating the hazard.
Evaluation of a hearing loss prevention program
monitoring and record keeping
- audiometric technician adequately trained, certified, records complete,
- OSHA standards,
- NIOSH recommendations, results communicated to supervisors, managers, and employees.
Evaluation of a hearing loss prevention program
referral
to outside sources for consultation or treatment
Evaluation of a hearing loss prevention program
hearing protection devices
made available to all employees whose daily average noise exposure is 85 dB or above.
Evaluation of a hearing loss prevention program
Administration
keeping organized and current (updated)on any changes in federal or state regulations.
