SILICOSIS
What is Silica?
Silica is the second most common mineral in the earth's crust
and is a major component of sand, rock, and mineral ores.
OSHA permissible exposure limit (PEL) is 100
μg/m3 for an 8-hour work exposure.
Silica exposure can be associated with:
Scleroderma
SLE
1.Autoimmune diseases : RA
2.Nephropathy
3.Tuberculosis
4.lung cancer
Silicosis
Silicosis is a disabling, nonreversible and
sometimes fatal lung disease caused by
overexposure to respirable crystalline silica.
Silicosis occur when workers are consistently
exposed to silica particles of respirable size (0.5–
5.0 μm in diameter) at levels exceeding those
recognized to be safe.
Between 1968 and 1990 there were 13,744
deaths in the US where the death certificate
mentioned silicosis.
PATHOGENESIS
• When fine particles of crystalline silica dust are
deposited in the lungs, macrophages that ingest the
dust particles will set off an inflamation response by
releasing tumor necrosis factors, interleukin-1,
leukotriene B4 and other cytokines. In turn, these
stimulate fibroblasts to proliferate and produce collagen
around the silica particle, thus resulting in fibrosis and
the formation of the nodular lesions. The inflammatory
effects of crystalline silica are apparently mediated by
the NALP-3-inflammasome
WHAT ARE THE TYPES
There are three types of silicosis, depending upon
the airborne concentration of crystalline silica to
which a worker has been exposed:
Chronic silicosis usually occurs after 10 or more
years of overexposure.
Accelerated silicosis results from higher
exposures and develops over 5-10 years.
Acute silicosis occurs where exposures are the
highest and can cause symptoms to develop within
a few weeks or up to 5 years.
Chronic Silicosis
• The most common form of the disease, may go
undetected for years in the early stages; in fact, a chest
X-ray may not reveal an abnormality until after 15 or 20
years of exposure. The body's ability to fight infections
may be overwhelmed by silica dust in the lungs, making
workers more susceptible to certain illnesses, such as
tuberculosis. As a result, workers may exhibit one or
more of the following symptoms:
• shortness of breath following physical exertion
• severe cough
• fatigue
• loss of appetite
• chest pains
Nodules >1 cm in diameter on a
X-RAY
background of small rounded
opacities characteristic of simple
silicosis:
- begins peripherally and
migrates centrally
- prominently in the upper
lobes .
As these fibrous masses in the
upper lobe progressively enlarge,
the hila are retracted upward and
the lower zones become
Accelerated silicosis
Accelerated silicosis is characterized by the same features as
classic silicosis except that the time from
• initial exposure to silica to the development of radio- graphic
changes and ensuing respiratory impairment
• is much shorter.
•
The chest radiograph may demonstrate rounded opacities as early
as 4 years after initial silica exposure.
Result of exposure to grossly excessive levels of dust.
Rapid progression to progressive massive fibrosis is associated with
severe respiratory impairment.
Acute silicosis
After a short duration of exposure to a high
concentrations of respirable free silica.
The worker has a relatively rapid onset of chest
symptoms and progressive respiratory impairment.
Deaths of a large number of these workers occurred
within a year after the onset of symptoms.
Progressive massive fibrosis
It is the result of the conglomeration of small rounded
opacities.
It has been traditionally recognized that progressive
massive fibrosis develops on a
background of advanced simple silicosis.
However, not all PMF patients have an advanced
degree of simple coal workers’ pneumoconiosis
Symptoms
The respiratory symptoms can be variable; ranging from only a
chronic productive cough to exertional dyspnea and, in some
persons, ultimately to respiratory failure.
Physical examination demonstrates decreased breath sounds,
and if the illness is extensive, signs of cor-pulmonale and
impending respiratory failure.
Crackles usually are not audible, and clubbing, if present, is
attributable to another cause.
ASSOCIATED ILLNESSES:
• Mycobacterial infections
• Carcinoma of the lung
• Connective tissue disease
Prevention &
management
Product substitution of silica with less toxic particles in
abrasive blasting
Control of air-borne dust concentration through
engineering interventions
Appropriate use of respiratory protective devices
Medical screening of silica-exposed workers is generally
recommended, using questionnaires, chest x-rays,
spirometry
Personal Protective
PPE against
Equipment
silica includes respirators and masks.
Respirators should be used only when the dust controls
cannot keep dust levels below the Recommended
Exposure Level.
There are many types of respirators, from air-
purifying to air-supplying and from a nose and mouth
covering to a full body respirator.
