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Silicosis in Construction
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By John A. Mineo - Director of Construction & Engineering
American Insurance Service Group
New York, New York
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 Crystalline
silica is the basic component of sand, quartz and granite rock. Airborne crystalline silica occurs commonly in both
work and non-work environments. Activities such as a sandblasting, rock drilling, roof bolting, foundry work,
stonecutting, drilling, quarrying, brick/block/concrete cutting, gunite operations, lead-based paint encapsulant
applications, asphalt paving, cement products manufacturing, demolition operations, hammering, chipping and sweeping
concrete or masonry, and tunneling operations can create an airborne silica exposure hazard.
Occupational exposure and inhalation of airborne crystalline silica can produce silicosis, a disabling, dust-related
disease of the lungs. Even materials containing small amounts of crystalline silica may be hazardous if they are used
in ways that produce high dust concentrations. Depending on the length of exposure, silicosis is a progressive and
many times a fatal disease that accounts for approximately three hundred deaths annually in the construction
industry, or 10% of all silicosis-related deaths annually.
Inhaling silica dust has also been associated with other diseases, such as tuberculosis and lung cancer. There is no
cure for silicosis, but it is a 100% preventable occupational disease.
| Silica exposure, an ancient hazard, is a very
serious threat to construction workers. Exposure to respirable crystalline silica dust during construction
activities can cause silicosis. Two million workers in the United States are exposed to crystalline silica every
year. The following report addresses the types and sources of silica, potential health effects and symptoms of
exposure, exposure assessment and control, work practices and procedures, and suggestions for reducing or
preventing silicosis. |
What Is Silica?
Silica is the name of a group of minerals containing silicon and oxygen in chemical combination
having the general formula SiO2. Silica may be free, in which case only SiO2 is present, or combined, in which the
SiO2 is combined chemically to some other atom or molecule. The difference is important to recognize, since the
silica problem exists only with free silica. Labels on materials and product analysis sheets (e.g., MSDS sheets) must
be read and instructions for use followed carefully.
Types Of Silica
Free silica may occur as amorphous-free silica, of which there are many forms, and
crystalline-free silica, of which there are five principal forms. Certain materials contain both amorphous- and
crystalline-free silica.
Silica-related diseases are associated only with crystalline-free silica. The most common examples of
crystalline-free silica are beach or bank sands. A third form of free silica is fused silica which is produced by
heating either the amorphous or crystalline forms. Other forms include cristobalite and tridymite.
Quartz, a principal form of silica, geologically is the second most common mineral in the earth's crust. Quartz is
readily found in both sedimentary and igneous rocks. Quartz content can vary among different rock types; for example,
granite can contain anywhere from ten to forty percent quartz; shales have been found to average 22 percent quartz;
and sandstones can average 70 percent quartz.
Exposure During Construction
The most severe worker exposures to crystalline silica results from sandblasting. In the
construction industry, sandblasting may be used to remove paint and rust from stone buildings, metal bridges, tanks,
and other surfaces. Other construction activities that may produce crystalline silica dust include jack--hammer
operations, rock/well drilling, concrete mixing, concrete tunneling, and brick and concrete block cutting and sawing.
Tunneling operations, repair, or replacement of linings of rotary kilns and cupola furnaces, and setting, laying, and
repairing railroad tracks are also potential sources of exposure.
Concrete and masonry products contain silica sand and rock containing silica. These products are primary materials
for construction, and construction workers may be exposed to respirable crystalline silica during activities such as
the following:
- Demolition or concrete and masonry structures.
- Crushing, loading, hauling, and dumping of rock.
- Chipping, hammering, and drilling of rock.
- Abrasive blasting using silica sand as the abrasive.
- Abrasive blasting of concrete (regardless of abrasive used).
- Sawing, hammering, drilling, grinding, and chipping of concrete or masonry.
- Dry sweeping or pressurized air blowing of concrete, rock, or sand dust.
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Effects Of Exposure To Crystalline Silica
 Silicosis
is one of the world's oldest known occupational diseases, dating back to ancient Greece. Since the 1800s, the
silicotic health problems associated with crystalline silica dust exposure have been referred to under a variety of
common names, including consumption, ganister disease, grinders' asthma, grinders' dust consumption, grinders' rot,
masons' disease, miner's asthma, miner's phthisis, potters' rot, sewer disease, stonemason's disease, chalicosis, and
shistosis. Silicosis was considered the most serious occupational hazard during the 1930s and was the focus of major
federal, state and professional attention.
Silicosis is the result of the body's response to the presence of silica dust in the lung(s). The respirable fraction
of the dust (particles generally considered to be smaller than five-millionth of a meter) can penetrate to the
innermost reactes of the respiratory systems. These are the alveoli (airsacs) where the exchange of oxygen and carbon
dioxide occurs. When workers inhale crystalline silica, they land on the alveoli, and white blood cells (macrophages)
try to remove them. However, the particles of free crystalline silica cause the macrophages to break open. The lung
tissues react by developing fibrotic nodules and scarring around the trapped silica particles.
Formation of large numbers of "scars" following prolonged exposure causes the alveolar surface to become
less elastic. This is noticed as shortness of breath following exertion. Symptoms seldom develop in less than five
years and, in many cases, may take more than 2 years to become disabling or cause death.
A worker's lungs may react more severely to silica sand that has been freshly fractured (sawed, hammered, or treated
in a way that produces airborne dust). This factor may contribute to the development of acute and accelerated forms
of silicosis.
| Factors Influencing the Development of
Silicosis |
| Development of silicosis is influenced by several
factors which include: |
- Form of the silica
- Content of crystalline-free silica in the dust
- Amount and kind of dust inhaled
- Relative size of the inhaled particles
- Length of exposure
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- Individual resistance
- Smoking habits
- Disease status
- Age
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Types of Silicosis
Workers may develop any of three types of silicosis, depending on the concentration of airborne
silica:
- Chronic silicosis, which usually occurs after ten or more years of exposure to crystalline silica at relatively
low concentrations.
- Accelerated silicosis which results from exposure to high concentrations of crystalline silica and develops five
to ten years after the initial exposure.
- Acute silicosis, which occurs where exposure concentrations are the highest and can cause symptoms to develop
within a few weeks to four or five years after the initial exposure.
Symptoms and Effects of Silicosis
 Early
stages of the disease may go unnoticed. Continued exposure may result in a shortness of breath on exercising,
possible fever and occasionally bluish skin at the ear lobes or lips.
Silicosis makes a person more susceptible to infectious diseases of the lungs, such as tuberculosis. Progression of
silicosis leads to fatigue, extreme shortness of breath, loss of appetite, pains in the chest, and respiratory
failure, which may cause death.
Medical evaluations of silicosis victims usually show the lungs to be filled with silica crystals and a protein
material. Pulmonary fibrosis (fibrous tissue in the lung) may or may not develop in acute cases of silicosis
depending on the time between the exposure and the onset of symptoms. Furthermore, evidence indicates that
crystalline silica is a potential occupational carcinogen.
ASSESSMENT
Current Exposure Limits
OSHA currently has a permissible exposure limit (PEL) for crystalline silica. Over 30% of
OSHA-collected silica samples from 1982 through 1991 exceeded the current PEL limit. The current OSHA PEL for
respirable dust containing crystalline silica (quartz) for the construction industry is measured by millions of
particles per cubic for (mppcf) and is calculated using the following formula:
| where PEL = |
250 mppcf
|
| |
% silica + 5 |
The current OSHA PEL for respirable dust containing crystalline silica (quartz) for general industry is measured by
(mg/m3) and is calculated using the following formula:
| where PEL = |
10 mg/m3
|
or |
250 mppcf
|
| |
%silica +2 |
|
% silica + 5 |
In addition, for cristobalite and tridymite forms, the same formula should be used for determining the PELs, divided
by one-half. The National Institute for Occupational Safety and Health's (NIOSH) recommended exposure limit (REL) for
respirable crystalline silica is 0.05 mg/m3 (50 mg/m3)
for up to ten hours/day during a 40-hour work week. NIOSH's position is that it is a carcinogen.
Suggested Measures To Control Exposures
Employers are required to provide and assure the use of appropriate controls or crystalline
silica-containing dust.
Elements which may be included in an effective program include:
- Ongoing personal air monitoring program*
- Dust control program
- Medical surveillance program/disease reporting
- Training and information to workers on crystalline silica*
- Availability of air and medical surveillance data to workers*
- Equipment maintenance program
- Respiratory protection program*
- Isolated personal hygiene facilities, eating facilities, and a clothing change area
- Record keeping
- Housekeeping program*
- Construction safety and health program*
- Regulated areas/warning signs
* Required by existing OSHA standards if an overexposure to crystalline exists.
Recommendations To Limit Exposures
There are many specific and general recommendations to reduce exposures to respirable
crystalline silica on the jobsite. Workers can limit their exposure by being aware of and practicing the following:
- Use type CE positive pressure abrasive blasting respirators for sandblasting.
- For other operations where respirators may be required, use a respirator approved for protection against
crystalline silica-containing dust. Do not alter the respirator in any way.
- Workers who use tight-fitting respirators may not be able to have beards or mustaches which interfere with the
respirator's seal to the face.
- If possible, change into disposable or washable work clothes at the jobsite; shower (where available) and change
into clean clothing before leaving the jobsite to prevent contamination of cars, homes, and other areas.
- Do not eat, drink, use tobacco products, or apply cosmetics in areas where there is dust containing crystalline
silica.
- Wash your hands and face before eating, drinking, smoking, or applying cosmetics in areas where there is dust
containing crystalline silica.
Additional general suggestions are as follows:
- Recognize where silica dust may be generated and plan ahead to eliminate or control the dust at the source.
- Use controls and containment methods, such as blast-cleaning machines and cabinets, wet drilling, or wet sawing
of silica-containing materials, to control the hazard and protect adjacent workers from exposure.
- Routinely maintain dust control systems to keep them in good working order.
- Conduct air monitoring to measure worker exposure and ensure that controls are providing adequate protection for
workers.
- Use adequate respiratory protection when source controls cannot keep silica exposures below the PEL.
- Post warning signs to mark the boundaries of work areas contaminated with respirable crystalline silica.
- Provide workers with training that includes information about health effects, work practices, and protective
equipment for respirable crystalline silica.
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