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training is crucial because it is vital that the workers understand why they
must wear the ear protection. If they know the purpose, then they are more
motivated to wear the protections and willing to participate in a hearing test.
The training should include and benefits of wearing the protection and
disadvantages if there were no protection from noise. Employers are required to
keep the noise exposure measurement records for two years. Employees
audiometric test records must remain on file throughout their employment

            A baseline
audiogram is taken to compare with a future audiogram of a person who exposed
to noise level above 85 dB at 8-TWA. It must complete within six months of
employment with the noise exposure level above 85 dB which require ear
protection. Employers must offer a variety of earplug and an earmuff that
employees can handpick (OSHA, 2002). Hearing protection equipment’s include
enclosures, aural inserts or earplugs, superaural protectors or canal caps, and
circumaural protectors or earmuffs (Puckett, 2017).  The employees can select whichever ones that
fit the best for them and comfortable to wear. The protector must provide
sufficient protection and prove to protect from high-level noise work
environment.  Currently, most business
owners use Noise Reduction Rating (NRR) to represent the ear protector’s
ability to reduce noise in a practical work setting. Then adjusts the NRR
according to the noise reduction in the actual working environment. It is the
employers’ responsibility to reevaluate the ear protection devices in use if
there is a change in a work environment that increases the noise level.
Employers must train employees how to use and care for the protection
equipment’s and oversee them on the job to make sure the workers wear them
appropriately (OSHA, 2002). The elements of selecting hearing protection should
include attenuation factors (NRR), job duties and environment, frequency and
duration of noise exposure and whether communication with other workers is
required (Puckett, 2017).

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            According to OSHA, employers
must monitor all the employees whose noise level exposure is greater than 85 dB
in a typical 8-hour work day. Noise-induced hearing loss can categorize into
temporary or permanent hearing loss. The temporary hearing loss is also known as
Temporary Threshold Shift (TTS) result from short-term exposure to noise.
Regular hearing return after a period of non-exposure or rest (OSHA, 2002). The
Standard Threshold Shift (STS) also known as the permanent hearing loss is
exposure to high noise levels over a period. It changes the hearing threshold
of a person with an average shift of 10 decibels (dB) or more at 2000 Hz, 3000
Hz, and 4000 Hz in at least one ear. STS is calculated from baseline audiogram
of individuals. The exposure measurement must clarify between three classes of
noise such as continuous, intermittent and impact noise. The continuous noise
is a broadband noise of constant pressure and frequency level. The intermittent
noise is exposure to broadband noise several times during a typical workday.
The impact noise is a noise that generates every less than one second (Puckett,

Hearing Conservation

hearing loss manifest in an adult due to age or job-related reason, he or she
can no longer hear high-frequency sounds. This manifestation can result in
individuals unable to distinguish the words begin with consonants such as s, f,
t, and z. An example would be not being able to hear the difference between the
“yes” and the “get.” A person can experience difficulties in everyday
conversation at work or with the family members. Individuals can still be able
to hear the words, but they cannot understand them. Communication is an
essential factor in social aspects of life. Almost all job requires excellent
communication skill to connect with the management, co-workers and the clients
efficiently. Without being able to communicate effectively due to hearing
impairment, it jeopardizes one’s career, image, and behavior. It can cause
potential danger to one’s safety in heavy machinery working environment (Sataloff,

What are the
consequences of hearing loss?

    The people who
readily exposed to carbon disulfide are workers from facilities that use the
chemical in their manufacturing practices. They may either incorporate the
compound primarily in the air or through the skin contact. About 10-30% carbon
disulfide is absorbed by the lungs, and less than 1% directly leaves the body
by urination. Approximately 70-90% is altered into a different form of
chemicals inside the body and leaves by urination. At very high level, this
chemical can cause an adverse effect on the nervous system. In animal studies,
it damages the heart. According to CDC, workers exposed to over 20 ppm carbon
disulfide during work hour for six months developed headaches, tiredness, and
trouble sleeping. Skin contact cause blisters in rayon plant workers who
touched fibers made from carbon disulfide. OSHA requires the level of carbon
disulfide not to exceed 20 ppm over 8-hour work day. NIOSH recommends that
average work environment air levels of this chemical not to exceed 1 ppm in
10-hours (ATSDR, 2015).        

disulfide in its pure form is a colorless liquid that has a sweet smell. The
impure compound of this compound is a yellowish liquid with an unpleasant odor
and mainly utilized in most industrial processes. Volcanic eruptions generate
carbon disulfide naturally. It is produced for industrial purposes by heating
carbon and sulfur together at a high temperature. Industries use carbon disulfide
as a base material to make things such as rayon, cellophane, and carbon
tetrachloride. The most substantial use of this solvent is the viscose rayon
industry. It is also used to dissolve rubber to produce tires and as a base
material to make some pesticides. When carbon disulfide is released into the
air, it evaporates very quickly. Since it is denser than the air, it tends to
stay closer to the ground. The accidental release of this compound into the
soil can cause contamination of the groundwater. When it dissolves into the
water, it is no longer can be broken down quickly. This chemical is very
flammable and explosive (ATSDR, 2015).

What is Carbon Disulfide?

            Styrene is
a human-made chemical. Its other chemical names are cinnamene, phenylethylene,
ethenylbenzene, and vinylbenzene. Styrene is the solvent that does not dissolve
in water. Products that made with styrene includes food containers, rubber,
plastic, insulation, pipes, fiberglass, and automobile parts. Styrofoam
products that made with long-chain styrene called polystyrene are popular among
the general population (ATSDR, 2011). 
One of the studies about styrene induced hearing loss contained a total
number of three hundred and thirteen participants from fiberglass industry,
metal manufacturing plants and a mail distribution center.        The data showed that workers that exposed
to styrene and noise had notable standard threshold shift at 2000, 3000, 4000
and 6000 hertz (Hz) when compared with non-exposed workers. This study also
revealed that the exposure to styrene below permissible level even has a
dangerous effect on human’s hearing system (Morata, Johnson, Nylen & Svensson,
2002). OSHA sets a limit for styrene exposure to 50 ppm for an 8-hour TWA (A
time-weighted average) and 100 ppm for 15-minute short-term exposure limits
(STEL). ACGIH and NIOSH have the same exposure limits as OSHA (Centers for
Disease Control and Prevention (CDC), 2011).

What is Styrene?

Environmental Protection Agency (EPA) sets a limit of no more than 1mg/L of
toluene in drinking water.  OSHA limits
workers who exposed to toluene not to exceed of 200 parts per million (ppm) in the
air in an average 8-hour workday. The National Institute for Occupational
Safety and Health (NIOSH) recommends no more than 100 ppm for toluene in the
air in a 10-hour workday. The American Conference of Governmental Industrial
Hygienists (ACGIH) recommends the toluene in workplace air not exceed 20 ppm
(average levels over 8 hours) (ATSDR, 2015).   

conducted in Sao Paulo, Brazil looked at one hundred and twenty-four
rotogravure printing workers who had exposure to various levels of noise and
organic solvent mixtures such as toluene, ethyl acetate, and ethanol. The
findings from this research suggest that exposure to toluene has a toxic effect
on the workers’ auditory system. The data collected show that forty-nine
percent of the workers had hearing loss. There were some variables taken into
consideration such as the age of the workers and their job duties, noise dose,
solvent concentrations in air, a biological marker of toluene, alcohol
consumption, and hippuric acid (the biomarker for toluene in urine). The odds
ratio estimated for hearing loss was 1.76 times greater for each gram of
hippuric acid per gram of creatinine in urine. The relative risk was four times
greater for the noise-exposed group compared with the unexposed group. The
relative risk is 11 times higher for the group exposed simultaneously to noise
and toluene, and five times greater for the group presented only to a mixture
of organic solvents (Morata et al., 1997).

            Day to day
exposure to toluene at work can cause tiredness, confusion, weakness, memory
loss, nausea and loss of appetite. These symptoms are temporary and will
disappear once the exposure is stopped.
However, a long-term daily exposure to toluene at the workplace can cause
permanent color vision and hearing loss. The effects of hearing loss with
exposure to toluene can increase when combined with conventional pain relief
medications such as aspirin and acetaminophen. Workers who repeatedly inhale
toluene from glue and paint thinners can damage their brain permanently. Other
symptoms may include problems with the speech, vision, hearing, loss of muscle
control, loss of memory, poor balance, and decreased mental ability. Constant
exposure to a high level of toluene can damage the liver and kidneys (ATSDR,

            Toluene is
clear, colorless liquid which exits naturally in crude oil and the tolu tree. The
process of making gasoline and making coke from coal produces toluene. It is
used widely as a solvent in making paints, paint thinners, nail polish,
adhesives, rubber, and in leather tanning and printing processes. Toluene is
also used as polymers to produce benzene, nylon, and plastics. It is also used
as an additive in gasoline to upgrade octane ratings. Toluene can release into
the environment via the air, water or soil from where it used or produced. It is commonly found in the atmosphere of dense
traffic areas. Toluene can get into the surface water and groundwater from
solvent or petroleum spills. Toluene can also leak into the groundwater from
the underground storage tanks leakage at the gas stations as well. When
products containing toluene are placed in
the landfills, it can enter the soil and water. However, toluene can break down
readily by either anaerobic or aerobic microorganisms in the ground When breath
in the air containing toluene, it is taken directly from the lung to the
bloodstream. After the body absorbs the chemical, most of it is removed from the body within a day. However,
a small amount may deposit in the fat tissue each time with the daily exposure.
The human body can turn toluene into the less toxic chemicals such as the hippuric
acid (Agency for Toxic Substances & Disease Registry (ATSDR), 2015).

What is Toluene?

scientific definition of noise is an unwanted sound. It is a hidden public
health issue which causes fatal car accidents, fatigue, infertility and hearing
loss with exposure within the community. Exposure to noise in the occupational
setting is unavoidable and cause irreversible damage such as hearing loss. The
risk factors associated with loud unwanted sound in a professional environment
includes noise intensity, frequency spectrum, total work duration, and the age
of the worker. The occupational hearing
loss is defined as the hearing impairment
of one or both ears because of one’s occupation. There are ways to minimize
exposure to heavy noise by using personal protective equipment and applying
administrative and engineering control measures. The occupational hearing loss
in the workplace is one of the most common occupational diseases in the United
States. Despite strategies to minimize the hearing loss in the workplace,
hearing loss is widespread in western nations with a sizeable industrialized
economy. A coexisting environmental risk factor can also cause a significant
hearing loss even with a low level of noise exposure. Organic solvents used in
the industry has shown to exhibit ototoxic effects in humans. Toluene and
styrene are highly utilized organic solvents which increased the probability of
hearing loss when combined with noise exposure. The other solvents compounds
that cause adverse effects on hearing include trichloroethylene, p-Xylene, n-Hexane,
and carbon disulfide. The solvent-induced hearing loss in humans impairs both the inner ear and the central
nervous system (Lataye, Campo, Pouyatos, Cossec, Blachere & Morel, 2003).

            The United
States government recorded that most of the disability benefits claims made by
the Veteran’s Health Administration are because of the hearing
impairments.  Good hearing is essential
for several military duties. The negative consequences of hearing loss may
include paranoia and psychotic-spectrum disorder. Research conducted by
Institute of Medicine in 2002 found approximately 10 to 18 percent of military
service members had a significant hearing threshold shift. Noise is also an
issue for nondeployed Airmen and workers from industrial occupations. Research
published by the National Health and Nutrition Examination Survey wrote that
nearly 22 million workers who exposed to hazardous noise levels having
difficulty hearing. One-third of the workers do not use hearing protection
while exposed to a high-level noise at work. Another study conducted in Great
Britain, studied 22,000 people from ages of five to sixty-four. The data showed
that 8 percent of the participants had hearing impairments. Also, loud noise
can cause an increase in blood pressure, ulcers and neurological complications (Shih,
Meadows, Mendeloff & Bowling, 2015).

            In a
functional hearing loss, there is no detectable organ damage inside the
auditory system. However, the patient suffers hearing loss due to psychological
or emotional issues. In clinical observation of this condition, the patient
does not respond to a conversation. The hearing difficulty might tie entirely
with emotional or mental etiology. The research from patient medical history
revealed that this state might affect due to the heredity or biological
references. The proper treatment may arrange if the psychological origin of a
functional hearing loss is recognized. In a central hearing loss, the damage is
in the central nervous system, and between the auditory nuclei and the cortex.
The physicians diagnosed that the patient in this condition cannot interpret or
understand what is being told. In this
state, the problem is not being able to hear the sound but the inability of the
brain to interpret what a person hears (Sataloff, 1987).

            The current
day prognosis of hearing loss is made by
observing the damages occurred at the auditory system. A hearing loss is categorized into following conditions such
as conductive, sensorineural, central, functional or a mixture of all. The
conductive hearing loss is a condition that interferes with the transmission of
sound through the external or middle of the inner ear. It can be corrected by utilizing hearing aid because
the patients just need the amplification. The sensorineural hearing loss is
also known as “nerve deafness” causes damage in the inner ear, the auditory
nerve or both. This condition is irreversible. The cochlea contains roughly
30,000 hearing nerve endings or hair cells. This disease causes damage to the
cochlear hair cells which connect to the brain. The sensorineural hearing loss
is the most complex condition because a large variety of diagnosis falls under
this category. A person who experienced a conductive hearing loss accompanied
by the sensorineural hearing loss in the same ear is diagnosed with a mixed hearing loss (Sataloff, 1987).

Hearing Loss and Occupational Noise Exposure

compounds contain two general classes such as workplace chemicals and
medication. Certain chemicals, like some medicine, have harmful effects on
hearing and balance. These are ototoxic chemicals. Ototoxic chemicals can cause
a hearing loss on their own. The hearing loss can be worse when exposed to both
the ototoxic chemicals and loud noises at the same time. Ototoxic had first
recognized in the 19th century. The effects of ototoxic substances do not
always have a cure. The signs and symptoms undergone from ototoxicity include
ringing in the ears, bilateral or unilateral hearing loss, dizziness,
non-coordination movements, unsteadiness in walking, and oscillating or
bouncing vision (Government of Western Australia, 2017).

Ototoxic chemicals –
chemicals that cause hearing loss

Ever since the Occupational Safety and Health Administration
(OSHA) established, researchers, give increased attention
to the workplace hazards and physical, chemical and biological factors that
influenced the workers’ health and well-being. Studies show there is an
association between hearing loss and the combined effects of exposure to
chemicals and noise. Laboratory experiments on animals exhibit the ototoxicity
of industrial chemicals such as organic solvents, metals, and asphyxiants. Many
chemical compounds have been shown to be ototoxic. Scientists currently believe
that there are more than 750 different groups of chemicals which are
potentially ototoxic. Chemical solvents and asphyxiants can also have a
synergistic effect on workers’ health when presented in conjunction with noise
(Morata, Fiorini, Fischer, Colacioppo, Wallingford, Krieg & Cesar, 1997).

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