Hearing Conservation
Terms
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OSHA standards
The threshold level is the A-weighted sound level at which a personal noise dosimeter begins to integrate noise into a measured exposure. for example... - if the threshold level on a SLM is set at 80 Decibels, it will capture and integrate into the computation of dose, all noise in the employee's hearing zone that equals or exceeds 80dB. Sound levels below this threshold would not be included in the computation of noise dose.
- What is the criterion level for noise exposure?
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is the continuous equivalent 8-hour A-weighted sound level that constitutes 100% of an allowable noise exposure
- the permissible exposure limit (PEL)
- For OSHA purposes this is 90dB averaged over an 8 hour period on the A scale of a standard SLM set on slow response - Noise measurements taken with an instrument set on the A weighting scale are expressed as
- dBA
- Paragraph 1910 of 1983 Hearing Conservation Amendment to the Occupational Noise Exposure Standard requires:
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-employers to administer a continuing effective hearing conservation program for all employees whose noise exposures equal or exceed an 8 hour time-weighted average of 85 dBA or equivalently a noise dose that is equal to 50% of the PEL
-The standard requires that all continuous intermittent and impulsive sound levels from 80 dB to 130 dB be included in the measurement of dose. In other words the threshold level for noise measurement purposes is 80 dBA - What is OSHA 's exchange rate
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The exchange rate is the increase or decrease in decibels corresponding to twice or half the noise dose. OSHA exchange rate = 5dB
-This means that the sound level of 90dB produces twice the noise that 85dB produces - Only instruments using a ___dB exchange rate may be used for OSHA compliance measures
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5dB
Dept of Navy use 4dB
Dept of Army and Air force use 3dB
NIOSH and EPA use 3dB - Exposure of a person with NH to workplace noise at levels equal to or exceeding the PEL may cause a shift in the worker's hearing threshold. Such a shift is called?
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A standard threshold shift and is defined as a change in hearing of an average 10dB or more at 2000 Hz, 3000Hz and 4,000Hz in either ear
- Workers experiencing standard threshold shifts are required by 29CFR 1910.95 to be fitted or refitted with
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-hearing protectors
-trained in their use
-and required to use them - In addition to effects on Hearing, Noise also:
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-interferes with understanding speech
-causes a stress reaction
-interferes with sleep
-lowers morale
-reduces efficiency
-causes annoyance
-causes fatigue - Paragraph 1910.95 of the 1983 Hearing Conservation Amendment to the Occupational Noise Exposure Standard requires employers to :
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-administer a continuing effective hearing conservation program for all employees whose noise exposures equal or exceed an 8 hour time weighted average (TWA) of 85dBA or equivalently a noise dose that is equal to 50% of the PEL
-The standard requires that all continuous, intermittent and impulsive sound levels from 80 to 130 dB be included in the measurement of dose.
in other words the threshold level for noise measurement purposes is 80dBA - What types of external conditions can affect noise measuring insturments?
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Temperature, humidity, atmospheric pressure, wind, and dust
Magnetic fields can also affect the performance of instruments - Temperature considerations
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should perform within design specifications over an ambient temperature range of -20degF to 140 degF.
- if temperature at measurement site is out of this range refer to the manufacturer.s specs to determine if the sound level meter or dosimeter is capable of performing properly - Effects of humidity on noise measurement
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OSHA noise instruments will perform accurately as long as moisture does not condense or deposit on the microphone diaphragm.
-if excessive moisture or rain is a problem in a given exposure situation, the Assistant Regional Administrator for Technical Support should be consulted - Effects of Atmospheric Pressure on noise measurement
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Both atmospheric pressure and temperature affect the output of sound level calibrators.
-Atmospheric pressure is more important of these two factors. When checking an acoustical calibrator, always apply the corrections for atmospheric pressure that are specified in the manufacturer;s instruction manual. - In general if the altitude of the measurement site is < _____ ft above sea level, no pressure correction is needed
- 10,000 ft
- If the measurement site is at an altitude ______ than 10,000 ft or if the site is being maintained at _____ than ambiant pressure
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higher
greater (like underwater tunnel construction)must use equation to correct the insturment reading
for high altitude location the correction will be positive for hyperbaric conditions correction will be negative - Effect of wind or dust on noise measurement?
- Wind or dust blowing across the microphone or the dosimeter or SLM produces turbulence which may cause a positive error in measurement. A wind screen should be used for all outdoor measurements or where indoors has significant air movement or dust
- Effect of Magnetic Fields
- Certain equipment and operations generate electromagnetic fields that can induce current in the electronic circuitry of SLM and cause erratic readings. If SLM used in such conditions the extent of field's interference should be determined by consulting the manufacturers instructions.
- Noise Dosimeters
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used by OSHA meet the ANSI standard S1.25-1978 "Specifications for personal Noise Dosimeters " which set performance and accuracy tolerances.
-For OSHA use the dosimeter must have a 5dB exchange rate, use 90 dBA criterion level, be set at slow response and use either 80 dBA or 90 dBA threshold gate - Sound Level Meters
- All SLMs used by OSHA meet ANSI standard s1.4-1071 or S1.4 -1983"Specifications for Sound Level Meters" which set performance and accuracy tolerances
- Sound level meters are used for:
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-to spot-check noise dosimeters performance
-to determine an employee's noise dose whenever a noise dosimeter is unavailable or inappropriate
-to identify and evaluate individual noise sources for abatement purposes
-to aid in the determination of the feasibility of engineering controls for individual noise sources for abatement purposes
-to evaluate hearing protectors - For practical purposes, this procedure should be followed for all sound level measurements
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-the microphone should be in the monitored employee's hearing zone
-OSHA defines the hearing zone as a sphere with a two foot diameter surrounding the head
-When noise levels at an employee's two ears are different, the higher level must be sampled for compliance determinations - Octave Band Noise Analyzers
- The type 1 SLM used by OSHA have built-in octave band analysis capability. These devices can be used to determine the feasibility of controls for individual noise sources for abatement purposes and to evaluate hearing protectors
- What do octave-band analyzers do?
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-they segment noise into its component parts
-the filter sets provide filters with the following center frequencies: 31.5, 63, 125, 250,1k,2k,4k,8k,and 16k
- the results may indicate those octave bands that contain the majority of the total radiated sound power
-they can assist CSHOs in determining the adequacy of various types of frequency dependent noise controls and also to select hearing protectors - For compliance purposes, readings with ANSI type 2 SLM and readings with a noise dosimeter are condered to have an accuracy of
- plus or minus 2dBA
- Readings with ANSI Type 1 SLM are considered to have an accuracy of
- plus or minus 1 dBA
- The results of the walk around survey are used to assist the CSHOin planning the work shift noise sampling strategy
- when screening for noise exposures, SLM measurement and estimates of exposure duration are sufficient. The resulting spot readings can be used to determine the need for a more complete evaluation . A SLM may be useful for this purpose
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OSHA was founded in ...
purpose was...
funded by.... - 1970 to ensure a safe working environment for employees. Is governmentally funded under the US dept of Labor. purpose is to create and enforce safety and health standards in the work place.
- NIOSH was estaglished concurrently under the
- Dept of health education and welfare to develop criteria for safe occupational exposures to workplace hazards
- The OSHA noise standard as amended does not cover all industries such as:
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-noise exposed workers in transportation
oil/bas well drilling and servicing
agriculture
constructionand mining
but the mining industry is regulate by 4 separate standards that are enforced my MSHA these vary in specific requirements - The generally accepted exposure limit for impulsive noise
- not to be exceeded for any time is a peak level of 140dBSPL
- The focus of the OSHA documents is prevention of occupational HL rather than
- conservation
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Prevention means
Conservation means -
to avoid creating HL
to sustain the hearing that is present regardless of whether damage has already occurred.
an emphasis on prevention evolves from beliefs that it should not be necessary to suffer an impairment, illness, or injury to earn a living and that it is possible to use methods to prevent occupational HL - Hearing protection devices
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-Earplugs - small inserts that fit into outer ear canal must be snugly sealed so the entire circumference of the ear canal is blocked, can be custom made
-ear muffs - fit over the entire outer ear to form an air seal so the entire circumference of the ear canal is blocked. Headband tension must be sufficient to hold earmuffs firmly around the ear.
-Properly fit earplugs or muffs reduce noise 15 to 30dB
earplugs better for low frequency noise and earmuffs better for high freq noise
-simultaneous use adds 10 to 15dB more protection than either used alone. Should be considered when noise exceeds 105dB
- helmets and Ear canal caps can be used as well - What is a Hear Kit
- hearing aid, ear mold, carrying pouch with education booklet and batteries
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Which of the following is a complete and accurate list of the signals required by federal regulations for monitoring audiometry in industry?
a)400,1000,2000,4000
b)500,1000,2000,6000
c)500,1000,2000,3000,8000Hz
d)250,500,1000,2000,4000,8000 -
e)500,1000,2000,3000,4000,6000
3k,4k,and 6k are often the most important frequencies to test for threshold shift, so all three of these frequencies must be included -
Under OSHA regulations adopted in March 1983, a standard threshold shift on an annual audiogram is defined as a change in hearing threshold relative to the baseline audiogram of an average of 10 dB or more at which of the following freq?
a) 500,1000,20 - C) 2000,3000,4000Hz