Objectives
What is sound?
How the ear works
How to measure noise
What does OSHA says about noise?
Hearing Conservation Program
Reading hearing tests
Hearing Protection
What is Sound?
Noise is generally defined as unwanted sound, we are all exposed to noise every day at home at work and in traffic.
Hertz (Hz)
Frequency a high or low pitch
Decibels (dB)
The loudness of the sound
Frequency
Humans can typically hear between 20 - 20,000 Hz
You can hear different frequencies better than others
Decibels
Sound pressure are measured in Decibels (dB) which is a logarithmic measure of sound pressure levels.
The quietest sound most humans can detect is 0 dB
Common Sounds
Anatomy of the Ear
How do we Hear?
The outer ear collects the soundwaves
The waves hit the eardrum, and cause it to vibrate
The vibrations are sent through the ear bones to the cochlea
Inside the Cochlea (snail shell)
Delicate hair cells vibrate to different frequencies
Hair cells detect the vibration, and send a signal to the brain
Loud sounds destroy the hair cells, and they stop functioning FOREVER!
The Ear does something else too!
The Semi-circular canals
Three tubes laying perpendicular to one another
Filled with fluid and tiny hair cells
Depending on which way your head is tilted, the fluid moves the hair cells, and they send a signal to your brain
Responsible for balance
How to measure noise
Decibels are measured on a logarithmic scale
Every time you add 6 dB, you double the sound pressure of the noise
Example
In the field, we determined the loudness of two compressors right next to each other
How loud is this area?
Do we add?
Do we add and take the average?
Neither, because it is a log scale
We use the following chart
82 dB + 83 dB = 86 dB
87 dB + 89 dB = 91 dB
How does the Safety Person determine noise levels
Sound level meter
Determine the loudness (dB) of noise at any given moment
Personal Dosimeters
Worn by employees
Measures the average loudness in an 8 hour work shift
“8hr. TWA” (Time Weighted Average)
What does OSHA say?
At 85 dB (8hr. TWA) (Action level)
Train employees
Make hearing protection available
Sample for noise levels
Do hearing tests
Notify employees of results
What does OSHA say?
At 90 dB or more
(100% Dose)
We must keep levels at or below 90 dB
Or require hearing protection that will lower noise levels to to 90 dB
What are Our Noise Levels?
|
Duration Per Day,
Hours
|
Sound Level dBA
|
|
8
|
90
|
|
6
|
92
|
|
4
|
95
|
|
3
|
97
|
|
2
|
100
|
|
1½
|
102
|
|
1
|
105
|
|
¾
|
107
|
|
½
|
110
|
|
¼
|
115
|
Hearing Conservation Program
Monitoring:
Employers should monitor noise exposure levels to identify employees who are exposed to noise levels at or above 85 dBA averaged over 8 working hours, or an 8-hour time-weighted average (TWA).
Noise level meters & Noise Dosemeter are used after being calibrated.
Audiometric Testing
Should the noise level monitoring determine that employees are being subjected to levels equaling or exceeding a TWA of 85 dBA, the next step is to establish an audiometric testing program for those exposed at no cost to the employee.
The important elements of an audiometric program include: Baseline audiograms, Annual audiograms, Control measures, Training, and follow-up procedures.
Baseline Audiograms
It is the reference audiogram against which future audiograms are compared.
Must be provided within 6 months of an employee’s first exposure at or above 8-hour TWA of 85 dBA. (Control measures should be taken)
Baseline Audiogram must be preceded by 14 hours without exposure to workplace noise.
Annual Audiograms
After baseline audiogram has been taken, each employee exposed to noise levels at the 85 dBA or above shall have annual examination.
Annual audiogram must be conducted within 1 year of the baseline.
Compared with baseline audiograms results.
Continued
To determine whether an employee has experienced any recordable hearing loss.
The hearing loss is reffered to in the OSHA standard as :Standard Threshold Shift (STS).
OSHA defines STS as “a change in hearing threshold relative to the baseline audiogram of an average of 10 dB or more at 2000, 3000, and 4000, Hz in either ear.
Audiogram
Control
The standard states that if the 90 dB PEL is being exceeded, “feasible administrative or engineering controls shall be utilized.
If fails, PPE shall be provided and used to reduce sound levels.
Administrative Controls
* Are defined as, “Methods of controlling employee exposures by job roration, work assignment, or time periods away from the hazards.
Engineering Control
Are defined as “ Methods of controlling employee exposures by modifying the source or reducing the quantity of contaminants released into the workroom environment.
Example: installing noise – absorbing acoustical foam or baffles to capture and deaden reverberating noise.
Hearing Protectors
Hearing protectors shall be made available and shall be worn by all employees exposed to an 8-hour TWA of 85 dBA or greaters.
Types of hearing protectors:
Ear muffs
Ear plugs
Ear canal
Hearing Protection
NRR - Noise reduction rating
Express - 25 NRR
Classic - 29 NRR
Max Lite - 30 NRR
DO NOT Subtract the NRR from the noise level
WRONG (109 dB - 25 NRR = 84 dB)
You must use the “Safety Factor”
Safety Factor
OSHA says the hearing protection is designed to reduce the noise by the NRR, but that is unlikely to happen due to :
Leaks in the seal
Vibration
Improper insertion
(NRR - 7) / 2
Example of NRR Protection
The noise at a large compressor is 109 dB
You are wearing the Express plugs with an NRR of 25
Do you have enough protection to place you below 90 dB level?
Hearing Protectors
Ear Plugs
Ear muffs
Training - Recordkeeping
Employees training is very important. All employees exposed to noise at a TWA of 85 dBA or greater shall participate in a hearing conservation training program.
An accurate records shall maintained of all employee exposure measurements.
A Final Note
Hearing is important
In time, noise levels at 85 dB can permanently damage your hearing
Wear your hearing protection both at work and at home
Choose hearing protection with a high NRR, and wear it properly
