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 exposure.

• 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 mailto:Pubstaft@NIOSDT1.em.cdc.gov., or download the document from the documents list at the NIOSH website at www.cdc.gov/niosh/.

OSHA Targets Silica Dust

On May 8, 1996, the Occupational Safety and Health Administration (OSHA) 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:

1. an outreach Program that involves the development of slides, informational cards, and a video on hazard recognition and control technology for crystalline silica;

2. the enforcement activities using worker's compensation data, injury and illness record-keeping data collected by OSHA, and NIOSH data from a cooperative agreement with state health departments to target inspection sites;

3. 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 Committee (ISO/CEN).

SKC Cyclone Sampler at 2.6 L/min
Collection Efficiency vs Aerodynamic Diameter

Likewise, NIOSH 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 Cut-Point 4 µm 5 µm Flow Rate 2.5 L/min 1.9 L/min

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

SKC Cyclones

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
Calibration Chamber
This aluminum device fits over the stem of the aluminum cyclone for calibrating the air flow. Cat. No....................225-01-03
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. Cat. No....................225-1

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 cassette holder.

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.

1. Assemble	2. Calibrate	3. Sample

SKC Sample Pumps, Filters and Accessories

PVC Filters for Sampling Silica
Manufactured from polyvinyl chloride (PVC), the SKC filters (GLA-5000^TM), 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.
Cat. No....................225-8-01

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).
Cat. No....................225-3

Cassette Opener
SKC E-Z Opener for separating cassette parts, suitable for both 25 mm and 37 mm cassettes.
Cat. No....................225-13-5

Filter Lifter
Stainless steel device that speeds removal of filter from cassette and prevents damage to membrane.
Cat. No....................225-13-7

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.
Cat. No....................225-25