Noise Flashcards
What is the purpose of the Eustachian tube?
releases pressure inside the ear by draining fluid into the throat
Describe the outer ear
outside of ear to the eardrum, channels and directs sound to the ear drum
What is the visible part of the ear and what is its purpose?
pinna
what is the purpose of the middle ear?
transfers sounds into electrical impulses
What is another name for the eardrum?
tympanic membrane
What is the purpose of the bone in the ear?
Bone transmits vibrations
What are some conditions that can impact the pinna?
Sunburn, frostbite, cauliflower ear
What are conditions of the ear canal?
packed wax, foreign objects, otitis (infection of the ear canal)
What are conditions of the ear drum?
Perforation or rupture (diving, blows, explosions)
What are conditions of the eustachian tube?
swelling, obstruction (allergy or infection)
What are conditions of the middle ear?
Bacterial infection, fixation of bones (bone disease)
What can cause damage to the chochlea?
infection, toxins, excessive vibrations, heavy metals, organic solvents, CO, noise induced hearing loss, age induced hearing loss
What are conditions related to the vestibular system?
labyrinthitis (vertigo, nausea, vomit), tumors
What is occupational hearing loss?
hearing impairment in one or both sides from one’s employment
What is acoustic trauma?
Injury to inner ear produced by one or few exposures to sudden intense acoustic forms of energy (explosions or blasts)
What is noise induced hearing loss?
Cumulative permanent loss of hearing developed over months or years of exposure
What factors determine duration and severity of hearing loss?
1) Sound level
2) Frequency of sound
3) Duration of sound - longer duration worse
4) Temporal distribution
5) Type of sound energy
6) Individual genetic and age factors
7) concurrent exposure to ototoxic compounds
What sound levels will make hearing loss more severe?
sound levels >60-80 dB
What frequency will make hearing loss more severe?
500- 200 Hz
Give examples of types of sound energy
Continuous vs. intermittent
What is sound?
any pressure variation that the human ear can detect. it produces a sensory response in the nerves
What is noise?
Sound that bears no information, often unpleasant and likely harmful
What are sound waves?
Vertical, vibrating plate causing small, repeated fluctuations in atmospheric pressure which propagate to the eardrum causing it to vibrate
Describe the frequency of sound (f)
number of times per second that an air molecule is displaced from its position of equilibrium, rebounds in opposite direction and returns to equilibrium
Horizontal distance between peaks
How is frequency measured?
Hertz (Hz)
How is frequency perceived?
pitch (high frequency noise is more annoying)
Draw the physics of sound
see slide
What would be the frequency of a soundwave with 2 cycles in 1 second?
2 Hz
What is amplitude?
loudness
What is frequency?
pitch
What is wavelength?
distance between two analogous points on two successive parts of wave- Distance a sound wave travels in one cycle
What is the velocity of sound?
speed of sound
always equal to product of wavelength and frquency
What is the equation for velocity?
c=f(wavelength)
velocity = frequency * wavelength
see slide to wavelength symbol
What is sound pressure?
Variations in atmospheric pressure that are detected by eardrum
How is sound pressure measured?
micropascals
N/m2
microbars
dynes / cm2
What are the common conversions for sound pressure?
1Pa = 1 N/ m2 = 10ubar = 10d/cm2
What is the decibel?
unit of sound - minimum perceptible difference i loudness
How does a decibel relate to a bel?
1/10 of a bel
What is intensity?
sound power, measure in W/m2
What happens to intensity as you move away from the source?
Diminishes with distance
What is a problem with intensity?
hard to measure
What tool measures sound pressure?
Sound level meters
What is the symbol for sound pressure level?
Lp
What is the unit for sound level pressure?
dB
What type of agent is noise?
Physical agent
What is the major concern with noise?
It can cause permanent hearing loss (permanent threshold shift)
What threshold shift can occur after one loud incident or minor blast?
temporary threshold shift
Hearing loss factors
- sound pressure level
- frequency of sound
- duration of exposure
What are the types of hearing loss?
Conduction Sensorineural Temporary vs. permanent threshold shift Tinitus trauma
Describe conductive hearing loss
- blockage, damage to eardrum
- not due to noise in most cases
Describe sensorneural hearing loss
- damage to inner ear or nerve
- chronic noise exposure does this
What is damaged by noise?
Hair cells
What are some of the problems with noise?
1) Distraction of workers –> accidents
2) Interference with communication –> accidents
3) Annoyance–> stress or violence
When is a hearing conservation program required?
> 85 dB over 8 hours
What is the goal of the hearing conservation program?
to prevent hearing impairment as a result of noise exposure on the job
What are the 5 components of the hearing conservation program?
1) exposure monitoring
2) audiometric testing
3) hearing protection
4) employee training
5) record keeping
What is the rationale for HCP?
- 20-30 million workers are at risk of irreversible hearing loss due to exposure and noise
- 9 million other workers are at risk of hearing loss from exposure to ototoxins
- to save on workers compensation costs
What are examples of ototoxins?
organic solvents, metals, CO
Name some elements of the hearing conservation program
- protect and conserve hearing
- person in charge
- measure baseline and ongoing exposure
- control of excessive exposure
- audiometric testing
- training
- SOP
- Program assessment
- Records
- Buy quiet
- other exposures
Main idea: develop the BEST program, not the required one
What are environmental risk factors for hearing loss?
- SPL of noise (intensity)
- Frequency of noise (type of noise)
- period of exposure (work duration)
- total work duration
- surroundings (noise reflected or absorbed)
What is the most important environmental risk factor?
Surroundings
What are host factors that impact hearing loss?
- distance of work situation from noise source
- position of worker’s ear due to work station
- years of employment
- individual susceptibility
- age
- co-existing loss or disease
- exposure outside of work
What are the most important host risk factors for hearing loss?
1) Age
2) Coexisting loss or disease
What equipment can be used to measure noise?
- sound level meters
- octave band analyzers
- noise dosimeters
What are the differences between sound level meters, octave band analyzers, and noise dosimeters?
Sound level meters: area- measure sound pressure variation in the air
Octave Band Analyzers: Area, brake noise down in frequency components for complex situations
Noise Dosimeter: Personal measurement- exposure monitors logging noise energy
What are the components of the meter?
- Microphone
- Amplifier
- Weighting Scale
- Output
What is the role of the microphone in a sound level meter?
Responds to sound pressure variations and produces and electrical signal
What is the role of the amplifier in the sound level meter?
Increases the output signal
What is the purpose of the weighting scale in the sound level meter?
electronically adjusts the amplification of frequencies giving some more amplification than others
What are the different weighting scales?
Flat, A, B, C scales
What is the most common weighting scale for sampling and why?
A, because OSHA standards are in the A scale (dBa)
What is the purpose of the output in sound level meters?
Digital display that shows dB
What can time weightings be set to?
fast, slow, or impulse
What determines how you set your time weighting?
how quickly you want the meter to respond to changes in sound
What can noise dosimeters determine?
- % of allowable exposure
- instantaneous current SPL
- Peak sound SPL
- Time History ** of exposure
- SPL average
- TWA*** sound pressure level
Name some work processes that would create noise levels above 85 dB
- Hand drill
- Chain Saw
- Belt Sander
- Table Saw
What is the threshold or threshold gate?
-lower limit of what SPL will be included
What is the criterion level?
OSHA standard of 90dBA, used to determine % of allowable exposure, it is the & of the criterion
Who is it important to interview for their ideas?
workers
What observations should be made while noise sampling?
- position relative to sources
- exposure and time
- obvious worker hearing problems
- noise source information
- surface materials
- controls & feasibility
Considerations for noise sampling
- diagrams
- locations of sampling/ workers
- data sheets
- checklist (NIOSH)
- Observations
What is the exchange rate?
Sound pressure increase or decrease that determines a halving or doubling of exposure time
What is another name for exchange rate?
doubling rate
What is the OSHA exchange rate?
5 dBA
What is the NIOSH exchange rate?
3dBA
Who follows the NIOSH exchange rate?
EPA, EU- 3dBA
Which exchange rate is based on physics?
NIOSH- 3 dBA
What is the DOD exchange rate?
4 dBA
What is sound power
total sound energy emitted by a source er unit time
Lw=10logW/Wo
What is W? Units?
Sound power (watts)
Lw=10logW/Wo
What is Wo? Units?
reference power (10^-12 Watts)
Lw=10logW/Wo
What is Lw?
Sound power level (dB)
What is the short method for adding decibels?
Use the table
0-1 dB difference =
+ 3 dB
2-3 dB difference =
+2 dB
4-9 dB difference =
+1 dB
10 dB or more difference
+0 dB
What is the equation for the TWA for noise?
Dose % = 100 [(C1/T1)+(C2/T2)+…]
Dose % = 100 [(C1/T1)+(C2/T2)+…]
What is the units for dose?
%- not units
Dose % = 100 [(C1/T1)+(C2/T2)+…]
What are the Cs?
individual exposure time (hours) at specific sound pressure levels
Dose % = 100 [(C1/T1)+(C2/T2)+…]
What are the Ts?
Allowable exposure time (hours) at specific sound pressure levels- find on OSHA site (or use NIOSH table based on exchange rate of 3dB)
Is TWA for sound the same as TWA for airborne agents?
NO
What is the alternative to expressing dose as a percentage?
express as a decimal
How does dose in decimal form compare to exposure standards?
> 1- overexposed above either the PEL or REL
>.05- above the action limit for OSHA (if using OSHA exchange rate)
If dose is expressed in %, what is the percent for over exposure? and percent for action limit?
> 100% & >50%
How long can someone stay in an area of a given SPL- equation
tallowed = T/ [2(Lp-Lcrit)/x]
tallowed = T/ [2(Lp-Lcrit)/x]
What is tallowed?
allowable exposure time (hours)
tallowed = T/ [2(Lp-Lcrit)/x]
What is T?
Base period, ususally 8 hours
tallowed = T/ [2(Lp-Lcrit)/x]
What is Lp?
Sound pressure level dBA
tallowed = T/ [2(Lp-Lcrit)/x]
What is Lcrit?
Criterion level (dBA)
What is x?
exchange rate (dBA)
When comparing to OSHA standards, what action should be taken if dose >85dBA?
baseline measurements & annual audioprograms
PPE required
Per OSHA standards, if PEL >90dBA, what actions are needed?
Noise control program
- engineering and administrative controls to reduce exposure to <90 dBA
Per OSHA, at what point is PPE required? At what point is PPE no longer adequate?
> 85 dBA, >90 dBA
What can you do at the source for noise problems?
- Modify
- Redesign
- Relocate
What can you do at the path level for a noise problem?
- enclosure
- absorption
- barrier
What can you do on the receiver end to reduce noise exposure?
- enclose
- absorption
- relocate
What is the cost of controlling noise at the source compared to controlling noise at the path?
1/10th the price to control noise at the source
What type of agent are the sources?
typically mechanical (vibrating or moving surfaces)
Why is sound considered to be aerodynaic?
unsteady flow of air, specific gas, or stream
How do you solve mechanical noise?
minimize the change of force (impact)
How do you solve aerodynamic issues with noise?
Minimize pressure changes/ turbulence
What are engineering controls for noise?
- use a quieter machine, process, or materials
- enclose the source
- decrease vibration
- decrease energy
- decrease driving force
- change directivity?
Name specific engineering controls to control noise problems from mechanical sources
- change the structure/ material of the source
- lubricate to decrease friction
- insulate (lagging)
- dampen the source
- Brace the source
- Decrease vibrating area**
- decrease resonance
- reduce dropping height
- decrease rotational speed
- improve the dynamic balance
- isolate vibration
What must you consider when enclosing the source of mechanical noise?
heat build-up
Give example of decreasing vibrating area
- using multiple belts instead of 1 thick belt
How does damping and bracing work as a control for mechanical noise?
makes the source stiffer and reduces vibrations
Give an example of insulating the vibration?
Add rubber around solid connecting arts
How is isolating vibration different than enclosing?
enclosing places machinery in room or area, isolating would be like putting up a noise barrier
Where there is turbulence, there is…
noise
What are engineering controls for aerodynamic noise?
- increase absorption of sound
- decrease reflection
- decrease reverberation
- increase distance from source to worker
- mufflers
- block the path with baffles
- enclose the worker
What do you need to increase absorption of sound/ decrease reflection, and decrease reverberation?
change of materials
What is an engineering control at the path level for noise?
- Increasing the distance
- Active noise control
By doubling the distance, you decrease SPL by…
6dB
How does active noise control work?
device generates a sound wave opposite or anti-phase of the source sound wave
Destructive interference –> ?
attenuation
What are administrative controls of noise?
- schedule noisy activities when fewest people are present
- rotate workers between quiet jobs & noisy jobs
- have very quiet rest areas and lunch areas
What are additional strategies to prevent noise exposure?
optimize preventative and emergency maintenance
- use specifications to buy quiet
What are two types of PPE to prevent noise induced hearing loss
- muffs (around outer ear)
- plugs (in ear canal)
How should you select PPE?
Select type based on noise and worker
Based on noise reduction rating
What NRR should you chose?
NRR with highest NRR
What NRR difference is meaningless?
<3 dB
Who gives the NRR for devices?
manufacturer
How do you determine the noise reduction from the NRR rating?
subtract 7, divide by 2, and add to env measurement
What are the limitations of NRRs?
Measure based on optimal conditions and trained workers
When do you require plugs & muffs?
> 105 dB
If there are multiple noise sources and noise is above 105 dB
take higher NRR and add 5 dB
What is the name for medical monitoring for hearing?
audiometry
What audiometry measurements do you need to take?
- pre-placement
- baseline
- annual
What does audiometry determine?
threshold for each ear and different frequencies
What is the requirement before the test?
Should be in quiet area 14 hours before test
What is the instrument for audiometry?
audiometer
Where is audiometry measured?
audiometric booth
What are the prescribed frequencies for audiometry testing?
- 500
- 1000
- 2000
- 4000
- 8000 Hz
What audiometry devide givs data?
audiogram
What considerations must be taken when analyzing results from audiometry?
- adjust for age
- compare to past thresholds
What is the standard threshold shift?
if average of losses at each frequency is greater than or equal to 10 dB
