Unit of measurement for frequency (pitch)
Hertz (Hz)
Unit of measurement for intensity (loudness)
Decibel (dB)
Risk of damage from noise
How loud (intensity) and how long (duration)
Steady-state or continuous noise, e.g. generator
Lasts 1 second or longer
Impulse or Impact noise, e.g. gunfire or nail gun
Lasts less than one second
Parts of the outer ear
Pinna and external auditory canal
Parts of the middle ear
Tympanic membrane, ossicles, eustachian tube
Eustachian tube (auditory tube)
Tube connecting the middle ear to the pharynx and equalizes middle ear space with atmospheric pressure
Conductive HL occurs here
Outer or middle ear
Sensorineural hearing loss
Hearing loss resulting from damage to the inner ear (cochlea) or the auditory nerve
Noise-induced hearing loss (NIHL)
Condition caused by the destruction of hair cells, the organs responsible for hearing, as a result of sounds that are "too long, too loud, or too close"; a sensorineural hearing loss
Mixed hearing loss
Combination of conductive and sensorineural types in the same ear
Middle ear bones (ossicles)
Malleus (hammer), incus (anvil), stapes (stirrup)
Possible early symptoms/signs of noise induced hearing loss
Tinnitus; difficulty understanding in presence of background noise; read visual cues
Auditory effects of noise
NIHL; tinnitus; hyperacusis
Non-auditory effects of noise
annoyancesleep disturbanceattentionmotivationstress reactionscardiovascular problemsendocrine problems
3 foot rule
Good rule of thumb to recognize hazardous noise exposure levels/situations: the rule is: if you have to shout at arms length (~3ft), in order to be understood over the background noise, then you're likely exposed to hazardous noise levels & should be wearing hearing protection to prevent NIHL
OSHA (Occupational Safety and Health Administration) versus National institute of Occupational Safety and Heath (NIOSH)
OSHA enforces regulation and NIOSH recommends best practice based on science and research
Sound pressure level (SPL) versus hearing level (HL)
SPL describes noise measurements taken with a sound level meter or dosimeter; HL describes Threshold levels obtained with an audiometer; 0 dB HL is not equal to 0 dB SPL
Noise Dosimeter
A sound measurement device used to record the amount of sound exposure over an extended period oftime (usually a work day)Personal vs. Area
Sound level meter
Uses a microphone to sense pressure variations in sound waves; the meter converts those pressures directly into decibels; provides a noise measurement that is a snapshot in time.
Time Weighted Average (TWA)
An evaluation of exposures that is time-weighted over an established period. It allow the exposure levels to be averaged generally over an eight-hour time period.
OSHA exchange rate
5 dB; for every 5 dB you go over the PEL of 90dBA TWA you half the allowable time of exposure
OSHA Action Level for noise
85dBA TWA
Sound Level Meter A-weighted Scale
OSHA requires this scale as it resembles how the human ear responds to sound (humans hear best from 500 Hz to 4000 Hz
Human Frequency Response at Birth
20 Hz to 20,000 Hz (20 kHz)
Human speech frequency range
250 Hz to 4000 Hz
Elements of a Hearing Conservation Program
Noise hazard assessment; engineering/administrative controls; annual hearing monitoring; annual training/education; hearing protection; recordkeeping
OSHA Noise Amendment
29 CFR 1910.95
Hughson-Westlake Procedure
Common procedure for obtaining threshold; the audiologist decreases stimulus intensity by 10 dB with a (+) response and increases by 5 dB with a (-) response
Hearing threshold level
Lowest intensity level responded to at least 50% of the time
Excessive noise levels will impact these test frequencies during a hearing exam
Low frequencies e.g. 500 Hz
First frequency always tested on an occupational hearing exam
1000 Hz
1000 Hz retest
Done as a validity check on first ear tested; thresholds should be within 5dB or should reinstruct patient and start test over
Presbycusis
A gradual loss of sensorineural hearing that occurs as the body ages
Professional Supervisor In a HCP
Responsible for oversight of Audiometric testing; reviews problem audiograms; must be an audiologist or physician
Elements of a Hearing Conservation Program
Mandatory and includes: exposure monitoring, audiometric testing, hearing protection, employee training, record keeping, and program evaluation
Noise Controls
At the source (preferred), along the path, at the receiver
Industrial Hygienist
Responsible for assessment of hazards that may affect workers as well as hazards that may impact the community.
NRR
Noise Reduction Rating; number determined in a laboratory
Hearing protection derating
OSHA recommends to reduce NRR in half
Hearing protection types
Noise reduction devices worn over the ear (noise muffs) or inside the ear canal (earplugs) in work or recreational settings with high noise levels
Best hearing protection
The one that is worn (consistently and properly)
Dual hearing protection NRR
After derating add additional 5dB of protection
Inverse square law for noise
For every doubling of distance away from a noise source you reduce the level by 6 dB
Noise doubling rule
If you add two identical noise sources you add 3dB to the Level (100 dB + 100 dB = 103 dB)
Administrative noise controls
Changes made by employer such as changing work schedules to reduce noise hazard risk to employees
OSHA standard threshold shift
10dB average change at 2000 Hz, 3000 Hz, and 4000 Hz, when compared to a baseline , in one or both ears
OSHA Recordable Standard Threshold Shift for Hearing Loss
3 criteria: 10dB average shift at 2, 3, and 4kHz, compared to baseline, AND 25 dB average HL at 2, 3, and 4 kHz in the same ear on current audiograms, AND determined to be work-related
Collapsing ear canal
Occurs naturally in some individuals during audiometric testing-earphones cause auricle to move forward collapsing the canal and causing an artificial hearing loss; Insert earphones should be used
Cochlea
A coiled, bony, fluid-filled tube in the inner ear through which sound waves trigger nerve impulses; damage from hazardous noise occurs here.
Microprocessor audiometer
Automated computer controlled audiometer
Tinnitus
A jingling; a ringing or buzzing in the ear
Type of hearing test done by a certified occupational Hearing conservationist (COHC)
Air Conduction Pure Tone Threshold Test
Hearing Threshold Level (HTL) are recorded on this
Audiogram (can be serial or graphic)
Baseline Hearing Test Must Be Done Within
6 months of starting employment (exception for mobile vans is up to 1 year)
Type of Hearing Loss that is treatable (medically or surgically)
Conductive hearing loss
Temporary Threshold Shift (TTS)
Brief exposure to intense noise that will ordinarily recover with auditory rest
Hearing Thresholds Tested are:
500, 1000, 2000, 3000, 4000, and 6000 Hz; 8000 Hz is optional but recommended.
Audiometric zero is:
0 dB HL; this is not an absence of soundHL scale has been normalized to healthy adult hearing
Vertical axis on a graphic Audiogram shows this:
Intensity levels which are measured in Decibels (softest at the top, loudest at the bottom)
Horizontal axis on a graphic Audiogram shows this:
Frequencies which are measured in Hertz (low to high going from left to right)
Hearing Baselines are reestablished when you have an STS because:
You don't want to identify the same shift each ear
#Days to notify individual of an STS in writing
21 days
OSHA versus NIOSH Noise Permissible Exposure Limit (PEL)
90 dBA PEL for OSHA; 85 dBA PEL recommended by NIOSH
OSHA recommendations for Audiometric Records
Maintain for duration of employment; NIOSH recommends duration of employment + 30 years
Sound Level Meter Microphone Type Required by OSHA
Minimum of Type 2 microphone
Formable Earplugs are:
Disposable when no longer return to shape and soiled
Pre-formed earplugs:
Can be washed with mild soap and water and reusable
Noise muff cushions
Should completely cover ear and seal against the face; cushions should be replaced when damaged and no longer seal effectively.
Hearing Aids and Hearing Test
Tests are to be done without hearing aids
Function of the Outer Ear
Collecting sound and sending it to the eardrum through the auditory canal
Function of the Middle Ear
Amplification of sound; lever action of the ossicular chain and the mismatch in size of eardrum and oval window amplify sound about 10 times
Function of the Inner Ear
Convert mechanical sound waves to neural impulses that can be recognized by the brain for hearing and balance
This type of hearing loss is treatable
Conductive hearing loss
When sound presented to the poorer ear crosses through the skull and is picked up by the better ear, this phenomenon is referred to as:
Crossover
The Action Level for OSHA and NIOSH is:
85 dBA TWA
Weighting scale required by OSHA for Hearing Conservation Program Noise Assessments:
A weighted scale; response resembles how the human ear responds to sound (humans hear best from 500-4000 Hz
This weighting scale is best for determining hearing protection attenuation
C weighted scale; has a flat response with all frequencies equally weighted
This Hearing Conservation Regulation is the minimum standard
OSHA Noise Amendment
Best audiometer for testing multiple stations
Microprocessor Audiometer
Best audiometer for testing difficult-to-test patients
Manual Audiometer
Calibration of audiometer performed daily with a electroacoustic simulator or human ear is called a:
Biologic calibration
A check of audiometer performed daily to ensure there are no intermittent problems with hardware is called a:
Functional Check