Helmke Under Fire
James A. Cranston
Director of Cleanroom Services
Virginia/Buckeye Micro Services
To the Editor:
In response to your article in the January 1996 issue regarding cleanroom laundries (“How to Choose a Cleanroom Laundry,” CleanRooms, Jan. 1996, p. 12), I felt it necessary to clarify several points with respect to garment “cleanliness” testing, as recommended by the RP003 Committee of Institute of Environmental Sciences.
Your article seemed to indicate that the most popular quality control test for cleanroom garment cleanliness utilized by certified cleanroom laundry processors was the Helmke Drum Test. It has been my experience–and others in the quality control business as applied to cleanroom laundries–that the ASTM-F51-68 Alt. B. Method is not only the preferred test for woven garments, but also the recommended procedure to be utilized for woven garments in the RP003 Standard.
Several attempts at “Round-Robin” blind-testing utilizing the Helmke Procedure have failed to prove that this procedure is repeatable and precise compared to the ASTM-F51-68 Alt. B. Method. Several reasons are evidenced by careful studies done by Lockheed (Sunnyvale, CA) in the early 1980s and were published in the Institute of Environmental Sciences` journals. No scientific study in recent years has ever validated the Helmke Procedure.
If one compares the results of particle counts attained by each method, it is no wonder that a cleanroom laundry might prefer the Helmke; however, if one is looking for real evidence of cleanliness, the ASTM method allows the operator to actually see contamination per square foot as well as count particles which are 5 micron or greater, and the method of recovery of those particles off the surface of the fabric is much more reliable than capturing particles that may fall off a garment in a small tumbling dryer and be inhaled by a 2-in. particle counter probe, as in the Helmke Procedure.
After all, the customer is really interested in an accurate analysis of the contamination on his/her garments per square foot after laundering, and not interested in a test method that makes the laundry “look good.”
Thank you for your interest in allowing me to clarify these two procedures for your readers.