Workers typically inhale
crystalline silica in abrasive blasting operations done
for the purposes of cleaning and removing paint from
metal surfaces, stone buildings and foundry castings, or
for finishing tombstones, etching or frosting glass, and
performing certain artistic projects. When crystalline
silica enters the lung, fibrotic nodules and scarring
can occur around the trapped silica particles. This
fibrotic condition of the lung is called silicosis. If
the nodules grow too large, breathing becomes difficult
and death may result. Silicosis victims are also at high
risk for developing active tuberculosis.
Workers may develop any of three types of silicosis depending
on the airborne concentration of crystalline silica:
- Chronic silicosis which usually occurs after 10 or
more years of exposure to relatively low concentrations.
- Accelerated silicosis which results from exposure
to high concentrations and develops 5 to 10 years after the initial
- Acute silicosis which occurs when exposures are very high
and symptoms can develop within a few weeks or up to 5 years after
the initial exposure.
For free information on how to prevent silicosis and deaths
from abrasive blasting, request Publication number 92-102 from
NIOSH at fax number 513-533-8573 or e-mail at
or download the document from the documents list at the NIOSH website
OSHA Targets Silica Dust
On May 8, 1996, the
Occupational Safety and Health Administration
announced a national special emphasis program on
crystalline silica to reduce the potential threat of
silicosis. The program applies to all workplaces under
OSHA's jurisdiction in the general industry,
construction, and maritime sectors. Key elements of the
special emphasis program include:
- an outreach Program that involves the
development of slides, informational cards, and a
video on hazard recognition and control technology for
- the enforcement activities using worker's
compensation data, injury and illness record-keeping
data collected by OSHA,
data from a cooperative agreement with state health
departments to target inspection sites;
- the designation of crystalline silica as a
priority for a future comprehensive rulemaking.
OSHA compliance officers
will be focusing their inspection on sites where silica
is not controlled effectively, and will limit their
inspections at sites where effective silicosis
prevention programs have been implemented. An important
part of an effective silicosis prevention program is
ongoing personal air monitoring.
The SKC Cyclone
The cyclone, named for
the rotation of air within its chamber, is a particle
size selector used in airborne particulate sampling. It
functions on the same principle as a centrifuge; the
rapid motion of air separates particles according to
their equivalent aerodynamic diameter. The cyclone is
placed in-line before a cassette that has been loaded
with the appropriate filter. The sampling device is then
connected to a sampling pump calibrated to a flow rate
specified for that particular type of cyclone. The pump
is clipped onto the worker's belt or placed into a
protective pouch and the cyclone is clipped onto the
worker's collar as close to the breathing zone as
possible. The smaller, respirable dust particles are
collected on the filter while the larger, nonrespirable
particles fall into the grit pot.
Sampling Efficiency Curves
The performance of
cyclones is typically described in terms of the 50% (or
median) cut-point. The median cut-point reflects the
size of dust that the cyclone collects with 50%
efficiency. As the particles get smaller, the cyclone
gets more efficient; with larger particles, the cyclone
gets less efficient. ACGIH
now specifies the median cut-point of a respirable dust
sampler to be 4 µm in accord with the International
Standards Organization/European Standardization
SKC Cyclone Sampler at 2.6 L/min
Collection Efficiency vs Aerodynamic Diameter
specifies the use of a cyclone with a 4 µm cut-point in
their 4th edition of Analytical Methods when sampling
for respirable crystalline silica or other respirable
dusts. This reflects an increase in the median cut-point
from the previous specification of 3.5 µm.
To comply with this change,
SKC now specifies flow rates that will achieve a 4 µm
cut-point for both the SKC aluminum and the new SKC
conductive plastic cyclone. Optional flow rates are
specified for those customers who want to follow the
more conservative collection efficiency curve
established by the British Medical Research Council (BMRC).
This curve specifies a median cut-point of 5 µm.
|SKC Aluminum Cyclone
Cat. No. 225-01-02
As Previously published, a flow rate of 2.6 L/min
will give a 4 µ cut-point, however, the new ACGIH/ISO/CEN
convention calls for the best match over the entire
curve which is given by 2.5 L/min (see bias map below).
The cyclone meets the NIOSH criteria for accuracy.
Bias map for SKC Cyclone at 2.5 LPM
Important Note About Cyclone Cut-points
The SKC cyclones are
designed to meet either the new ACGIH/ISO/CEN (Soderholm)
curve with 4 µm cut-point or the BMRC curve with a 5
µm cut-point depending upon the flow rate used. Note,
however, that per the federal regulations, OSHA
inspectors must use cyclones that meet the old ACGIH
curve with a 3.5 µm cut-point. SKC cyclones follow more
conservative curves which means they will sample on the
side of safety when compared to cyclones used by OSHA
inspectors. Based on extrapolation from our calibration
experiments the optimum flow rate for the SKC aluminum
cyclone to meet the old ACGIH convention is 2.7 L/min.
|SKC Aluminum Cyclone
|The SKC aluminum cyclone gives sharp size
selection between respirable fractions at
4 or 5 microns depending on the flow rate used.
Aluminum construction eliminates the problems
associated with nylon cyclones that often give
low results due to static charge buildup.
37 mm, Cat. No....................225-01-02
|This aluminum device fits over the stem of the
aluminum cyclone for calibrating the air flow.
|Filter Cassette Holder
|A lightweight filter cassette holder designed
for attaching to a worker's collar, accommodating three-piece 37 mm cassettes
with or without a cyclone.
SKC Cyclones - Assembly and Operation
Load the desired filter and
support pad into a 3-piece cassette. To insert the
cyclone, remove the entire inlet section of the cassette
(not just the plugs) and press the cyclone firmly into
the center ring of the cassette. Place the
cyclone-cassette assembly into the cassette holder by
inserting the stem of the cyclone through the large hole
and clicking the cyclone's pin into the slot in the
Stretch the spring-loaded
hold-down plate of the filter cassette holder over the
cassette. Insert the adapter located in the end of the
short piece of rubber tubing through the hole in the
hold-down plate and into the cassette.
Calibrate the pump with the
cyclone-cassette assembly in line using a primary
standard calibrator such as the SKC UltraFlo Electronic
Calibrator. Attach the pump to the worker and clip the
cyclone-cassette assembly as close to the breathing zone
as possible. Activate the pump. The pump remains in
position on the worker for the entire sampling period.
At the end of the sampling period, remove the
cyclone/cassette assembly from the holder. Separate the
cyclone from the cassette and replace the inlet section
of the cassette for transport to the lab. Remove the red
cap from the cyclone, clean out the contents, and
replace red cap on the cyclone.
SKC Sample Pumps, Filters and Accessories
Combines the power needed to do full-shift silica
sampling with the versatility needed to do low flow gas
& vapor sampling
The Universal Solution
The battery-operated PCXR8 sampler is ideal for silica
sampling as well as other on-worker and fenceline
applications. The easy-to-operate, on-board computer of
the PCXR8 gives you unsurpassed flexibility. You can
program a delayed start time for your test (e.g., during
the night shift), an automatic shutdown time, or both.
Accuracy is ± 0.05% (± 45 sec/day). The current
"Elapsed Sampling Time" reading appears
continuously on the large LCD. By pressing the
appropriate key you can instead display total elapsed
time (including time delay) and pump run time.
PCXR8 Personal Sample Pump (5-5000 ml/min)
PVC Filters for Sampling Silica
Manufactured from polyvinyl chloride (PVC), the SKC
are silica-free for sampling silica or other
gravimetrically determined contaminants. Their smooth,
defect-free surface makes them suitable for gravimetric
or microscopic analysis.
Low ash, low moisture pickup, and light tare weight
assure gravimetric stability; support pads included
(require 3-piece filter cassette blanks when used with
aluminum cyclone), 5.0 µm pore, 37 mm.
SKC supplies a wide selection of PVC filters in
various package sizes, specifications, and preloaded
cassettes. Contact the SKC sales department for more
information on PVC filters.
Filter Sampling Accessories
Filter Cassette Blanks
3-piece filter cassette blanks, clear polystyrene, for
use with the aluminum cyclone, 37 mm (also available in
economy packs of 50).
SKC E-Z Opener for separating cassette parts, suitable
for both 25 mm and 37 mm cassettes.
Stainless steel device that speeds removal of filter
from cassette and prevents damage to membrane.
Cassette Sealing Bands
Self-sealing bands seal filter cassettes during sampling
and transport. Suitable for 37 mm cassettes, they are 1
inch wide (2.5 cm) and provide a smooth writing surface
for sample identification.