OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

February 21, 1989


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.

The cyclones shipped with the SKC medium flow air sampling pumps for respirable dust sampling are made of metal and have been calibrated at a flow rate of 1.9 liters per minute (LPM) which is different from the 1.7 LPM required for the nylon cyclone.

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)