February 21, 1989

MEMORANDUM FOR:   REGIONAL ADMINISTRATORS

ATTN:             ARA's for Technical Support

THRU:             LEO CAREY Director
                 Office of Field Programs

FROM:             EDWARD J. BAIER Director
                 Directorate of Technical Support

SUBJECT:          Cyclones Supplied by SKC Inc.

SKC indicated that these metal cyclones were purchased from Sweden and it was designed from the collection criteria established by the British Medical Research Council (BMRC). The nylon cyclones supplied to our CSHOs are based on the collection criteria recommended by the American Conference of Governmental Industrial Hygienists (ACGIH). Their major difference is the cut-off size. The nylon cyclone has a 50% collection efficiency at 3.5 micrometers while the SKC cyclone has a 50% collection efficiency at 5.0 micrometers (see attached table for details).

Since the two collection efficiency curves are quite different and are not compatible, the SKC cyclones are not to be used for collection of respirable dust. All SKC cyclones should be returned to the OSHA Cincinnati Laboratory for replacement by the nylon cyclones.

If your staff is interested in respirable dust sampling, the ACGIH publication "Air Sampling Instruments" has an excellent chapter on this subject (Size-selective Health Hazard Sampling by Morton Lippmann).

Please contact Ching-tsen Bien of my staff at FTS-523-7065 if you have any questions.

(For Attachment, see printed copy)