T.R. Consulting, Inc. Monthly Safety Article
October 2002
Compiled and Written by: Tony Rieck
T.R. Consulting, Inc.
T.R. Consulting, Inc. publishes monthly safety articles. For a list of archived articles go to www.trconsultinggroup.com/safety/archive.html
Noise-induced hearing loss is a common occupational problem. Approximately 30 million workers are exposed to hazardous noise while performing their job duties and as many as ten million additional workers are at risk of hearing loss due to exposure to solvents, metals and other agents. Noise-induced hearing loss is 100 percent preventable. Yet, once the hearing loss has occurred, the hearing loss is permanent and irreversible. Preventative measures include engineering controls (such as mufflers and acoustic barriers) and personal protective devices (ear plugs and muffs). Ear plugs and muffs are chosen only when engineering controls are not feasible or inadequate. All workplaces where hazardous levels of noise can be encountered should institute a hearing loss prevention program. These hearing conservation programs should include noise assessments, engineering controls, employee education, guidelines for the selection and use of hearing protection devices, audiometric tests to monitor worker hearing/hearing loss, recordkeeping methods, and program evaluation.
The following topics are presented in this article:
* Noise Control Methods
There are two types of noise exposure that can lead to hearing loss: acute exposure, termed “occupational acoustic trauma”, and chronic exposure, termed “occupational noise-induced hearing loss”. Occupational noise-induced hearing loss is a slowly developing hearing loss over a long period as the result of exposure to continuous or intermittent noise at hazardous levels. Occupational acoustic trauma is a sudden loss of hearing resulting from a single exposure to a sudden burst of sound. Once the exposure to hazardous levels of noise is discontinued, there is no significant progression of hearing loss. Additionally, those having suffered from noise-induced hearing loss are not more susceptible to further hearing loss nor are they more sensitive to hazardous sound levels encountered after the time of impairment. A diagnosis of noise-induced hearing loss needs to be made by a physician and should include a historical assessment of noise exposure.
Sounds can be
divided into two categories: continuous
and intermittent. Intermittent sounds
are sounds that have maxima (peaks) at intervals of one second or more. Continuous sounds are sounds that are either
uninterrupted or that have maxima at intervals of less than one second. A hammer striking a nail every 1.5 seconds
is an intermittent noise source. The
same hammer striking the same nail once every 0.5 seconds is a continuous noise
source. Exposure to continuous noise
sources is considered more hazardous than exposure to intermittent noise
sources of the same sound level because the intermittent exposure allows the
ear to have a brief rest period between peaks.
Exposure to sound levels at or above 85 decibels has the potential to
cause hearing loss.
Some common noise
exposures are listed below (from NIOSH Sound Meter):
*
Whisper 30dB
*
Normal
Conversation 60dB
*
Ringing Telephone 80dB
*
Hair Dryer 90dB
*
Power Lawn
Mower 90dB
*
Belt Sander 93dB
*
Tractor 96dB
*
Hand Drill 98dB
*
Impact Wrench 103dB
*
Bulldozer 105dB
*
Spray Paint
System 105dB
*
Gas Chain Saw 110dB
*
Hammer Drill 114dB
*
Pneumatic
Percussion Drill 119dB
From the above, it
becomes obvious that we are exposed to potentially hazardous levels of noise as
a part of our every day lives and that many of us are exposed to these same
potentially hazardous levels of noise as a part of our work as well. Exposure to excessive noise in our daily
lives tends to be more limited than the same exposures at our place of
employment. Mowing your own lawn and
drying your hair using a hair dryer may expose an individual to hazardous
levels of noise for a few hours a week.
However, the landscaping employee may be exposed to six or more hours of
hazardous noise each day as would an employee working in a hair salon.
Much like the
allowable exposure to chemicals, allowable exposures to sound are calculated
based on a time weighted average exposure (TWA). The following chart provides information on the duration per day
(HOURS) of allowable employee exposure to noise in the workplace based upon the
OSHA Permissible Noise Exposure as listed in Table G-16 of 29 CFR Part 1910.95
(OSHA) and values provided in the CDC hearing conservation program for CDC
employees (NIOSH/ACGIH). Note that the
OSHA values are the maximum acceptable under regulation. The CDC program limits are more protective
than the limits established by law and were derived from the ACGIH Threshold
Limit Values (TLV) for noise exposure.
Sound levels are measured in dBA using the slow response mode.
16 85 80
8 90 85
4 95 90
2 100 95
1 105 100
½ 110 105
¼ 115 110
1/8 120 115
Note: Additional values are provided in Table G-16
of 29 CFR Part 1910.95 for exposure values between below and above those
provide in this chart.
Calculations of
variable exposures throughout the day can be calculated as the sum (S)
of the actual hours of exposure at a noise level (T) divided by the
allowable hours of exposure at that level (H) for each of the different
exposures. If the value of S is
greater than 1.0, the TWA has been exceeded.
The formula for the calculation is provided below:
T1 T2 T3
--- + --- + --- + . .
. . = S
H1 H2 H3
Using this formula,
it is possible to check the compliance of an employee exposure. For example, if an employee is exposed to 95
dB for 1 hour of an 8 hour workday, 90 dB for 4 hours of the workday and 85 dB
for the remaining three hours of the workday, the calculation would be as
follows:
1 4 3
--(95dB) + --(90dB) + --(85dB) = 0.9375
4 8 16
Since the result (S)
is less than (or equal to) 1.0, the employee exposure is compliant with the
standard. Because the standard is based
on an 8 hour workday, a longer workday would require that employees be exposed
to somewhat lower levels of noise throughout the workday.
Not all employers
are required to measure the level of employee exposure to noise in the
workplace. Noise monitoring or
measuring is only a requirement when employee exposures are at or above 85dB
(TWA). The employer would be wise to
begin measuring the noise levels in the workplace if there have been employee
complaints, normal conversation is difficult, specific equipment is provided by
the manufacturer with information indicating that the 85dB threshold may be
exceeded, or there are any indications that employees are losing their
hearing. If there is a question as to
the need for a noise monitoring program, actual workplace noise measurements
are a useful diagnostic tool. If
employees are exposed to a TWA noise exposure of 85dB or more, a hearing
conservation program needs to be implemented.
A hearing
conservation program begins with a written plan that tells how the employer is
going to monitor the exposure of workers to noise, reduce employee exposures to
noise, train and equip employees, and verify the effectiveness of the hearing
conservation program. The typical
elements of the program are outlined below.
EMPLOYER HEARING
CONSERVATION POLICY
This section of the
plan tells employees and other interested parties about the reasons that the
employer has instituted a hearing conservation program, the goals of the
program and how the program is organized.
This section should also describe how the policy is accessible to
interested parties.
ASSIGNMENT OF
RESPONSIBILITY FOR THE PROGRAM
Administrators,
trainers, supervisors and employees all have responsibilities necessary for the
successful implementation of the hearing conservation program. This section should also be used to
designate employees and job duties affected by the implementation of the
hearing conservation program.
EVALUATION/MONITORING
OF NOISE LEVELS
In order for the
hearing conservation program to be effective, several topics need to be addressed. Areas where hazardous noises are generated
need to be identified. Appropriate
measurements of noise levels need to be obtained. Personnel monitoring may be required for employees that move from
one area to another as a part of their activities. Initial measurements of noise levels need to be periodically
repeated and verified, and changes in equipment or acoustic controls may
require reevaluation.
NOISE CONTROL
METHODS
This section of the
plan should spell out the engineering controls that are in place, standard
operating procedures that reduce noise exposure, administrative controls and
the types of hearing protection devices that are available to employees. Administrative controls should include
information on signage that is provided to alert employees to the need for
hearing protective devices in areas where hazardous noise levels might be
present. Information on the types of
hearing protection devices available to employees should include policies for
issuance, use and maintenance of hearing protective devices.
MEDICAL SURVEILLANCE
This section of the
plan details the way that employees will be notified, and explain the program
for baseline and annual audiometric tests.
TRAINING
The training needs
to include: symptoms of overexposure to
hazardous noises, the recognition of probable sources or conditions indicative
of hazardous noise, information about the progression of noise-induced hearing
loss, employer procedures related to hearing protection devices, advantages and
limitations of hearing protection devices, noise measurement procedures, and
the requirements of the hearing conservation program.
HEARING CONSERVATION
PROGRAM EVALUATION
This section
provides information on how employees can provide input about the program, how
audiometric testing will be used as a part of an evaluation process, and
whether the employer will use an outside third party to verify the
effectiveness of the program.
RECORDKEEPING
This section states
where records are to be kept and length of time that the records will be
maintained. This section will include
any safeguards to be implemented to prevent unauthorized access and to assure
access to those entitled to review the records.
The above outline
represents a very basic approach to the written hearing conservation plan. It is also helpful to include as appendices
a copy of the regulations of 29 CFR Part 1910.95 and a copy of the most current
training materials related to the program.
Once the plan is written and implemented, the hearing conservation program
is in place.
Two instruments used
to measure noise exposure are the sound level meter and the dosimeter.
The sound level
meter provides a “snap shot” of the noise at a given instant in time. Multiple measurements taken at different
times throughout the day can provide an estimation of the noise exposure
associated with the area where the meter is placed. Where there is significant fluctuation of noise levels (such as a
noise source that regularly cycles on and off), the length of time that the
noise remains at each level is determined.
This procedure is repeated at different locations within the workplace
allowing for the creation of a sound level map. Estimates of individual exposure are made by taking information
on typical employee movement throughout the workplace. This method of noise level monitoring is
called area monitoring.
Dosimeters are
typically used for personal monitoring.
The dosimeter is attached to the employees outer garment and a microphone
is placed in the hearing zone of the employee.
The dosimeter records the sound levels during the test period, providing
an average noise exposure for the test period.
There are three
methods available for controlling worker exposure to noise: engineering
controls, administrative controls and personal hearing protective devices. Engineering controls, if feasible, are the
first option. Where engineering
controls are not feasible or are inadequate to reduce employee noise exposure
to acceptable levels, administrative controls are the next preferred
method. Personal hearing protection
devices are used as a permanent means of noise exposure reduction only after
engineering and administrative controls have proven inadequate or unfeasible.
Engineering Noise
Control – any modification
or replacement of equipment or related physical changes either at the noise
source or along the noise transmission pathway that results in a reduction in
the noise level at the employee’s ear.
Mufflers and acoustic barriers are examples of engineered noise
controls.
Administrative
Noise Control – any change
in work schedules or operations that result in a reduction in employee noise
exposure. Increasing the distance
between a noise source and a workstation, and rotation of employees between
areas of greater and lesser noise exposure are examples of administrative noise
controls.
Earplugs and earmuffs are the two categories of personal hearing protection devices. Hearing protective devices have NRR (Noise Reduction Ratio) ratings. Employees must be trained in the proper use, selection and maintenance of hearing protective devices that they might use. In all instances, the NRR rating of the selected hearing protection device must be sufficient to reduce the noise at the ear drum to 85 dBA or less. While the use of both earplugs and earmuffs may reduce the level of sound exposure beyond that achieved with either earplugs or earmuffs by themselves, the protection is not additive (NRR 29 earplugs + NRR 23 earmuffs does not equal NRR 52 protection). It is also important to understand that the maximum sound attenuation achieved when wearing any hearing protection device is limited due to the ability of noise surrounding the head and body to be transmitted to the inner ear through tissue and bone pathways.
Premolded Earplugs – usually designed as either single or triple flange inserts, premolded earplugs are pliable devices of a fixed size.
Formable Earplugs – usually cylindrical or torpedo shaped, formable earplugs are rolled between the fingers, inserted into the ear canal and held until they expand to provide a snug fit. Some formable earplugs are equipped with cords.
Custom Molded Earplugs – an option available to those who cannot be properly fitted with either premolded or formable earplugs.
Earmuff – a device worn around the exterior of the ear to reduce the level of noise that reaches the ear. An air tight seal between the cushions of the earmuff and the wearer’s head is essential for proper protection when wearing ear muffs.
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