Particle counters and practices step up to ISO calibration standard


By George Miller

The recent passage of an international standard for particle-counter calibration–ISO 21501-4–is having a ripple effect among contamination control practitioners: Suppliers who make particle counters are ensuring standards compliance in their products; the promulgators of recommended practices are working to ensure that existing practices align with the new standard; and manufacturers who use ultra-clean rooms, especially those in regulated industries, are considering how–and how quickly–to bring existing operations into compliance.

Among those in the first category is Hach Ultra (Grants Pass, OR), which announced in August the MET ONE 7000 series remote air particle counters that meet ISO 21501-4 requirements.

The standard updates and supersedes an existing Japanese spec, JIS B 9921, as well as an ASTM International standard practice for calibration of airborne particle counters.

Metrology and calibration details

“The new standard is similar to the Japanese standard that we’ve been using for some time,” says Jerry Szpak, director for research and development at Hach Ultra. “But it has made some steps in illuminating details on metrology and calibration.” (See “Achieving Particle Counting Accuracy,” CleanRooms, p. 36, July 2008.)

He adds that the new standard and the existing Recommended Practice from the Institute of Environmental Sciences and Technology (IEST-RP-CC014.1, Calibration and Characterization of Optical Airborne Particle Counters) are somewhat different in terms of resolution and maximum particle concentration specifications. Szpak says the Recommended Practice should be revised to comply with ISO 21501-4.

Software upgrades and changes to calibration processes and procedures differentiate the ISO-21501-4-compliant MET ONE 7000 series from earlier Hach Ultra particle counters. Photo courtesy of Hach Ultra.
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Recommended Practices (RPs) are usually developed in the absence of a standard. In fact, they are often used when standards are being developed, according to David L. Chandler, chairman of the IEST CC014.1 Working Group and engineering manager at Climet Instruments Co. (Redlands, CA).

“Both the Japanese and ISO standards include acceptance criteria, whereas the RP contains procedural information. That’s where they differ,” says Chandler. “The RP’s two sections on counting efficiency, for example, run five pages, covering primary and secondary methods. The ISO standard has just five sentences on the same topic, plus a one-page annex.”

As far as aligning with the existing standard, the ISO standard contains a response-rate spec–how fast the instrument responds to changes in particle concentration, Chandler says. The RP includes nothing about that. ISO also covers size settings, while the RP does not.

Filling the gaps

“So we’ve identified these areas that have now become standardized and that could benefit from procedural details. We’re currently working to fill those gaps,” says Chandler.

Among the more important aspects of the new standard, according to Chandler, is that it states that the calibration at every interval should include size calibration, size resolution, and counting efficiency verification. “This is a big deal if a customer’s current equipment cannot meet that standard,” he says.

He adds that Climet particle counters, which have long included counting efficiency verification on calibration certificates, already comply with the new standard. “That comes standard with the purchase of a new unit and is available for subsequent factory calibrations. It is a new thing for field calibrations,” notes Chandler.

Regarding customers, Chandler says he is unsure how quickly users will have to make changes to particle counters already in use. “It depends on how strongly they enforce the standard,” he says. “Companies overseen by regulators would probably have to comply more quickly than companies in an unregulated environment, who use counters to improve their manufacturing yield.”

FDA drives move to remote units

Matt Smith, Hach Ultra marketing manager for life sciences, identifies the U.S. Food and Drug Administration among regulators having the greatest impact, based on the increased scrutiny of manufacturing processes it is requiring of drug and medical device makers. “As life sciences companies push into continuous monitoring, more of them want to change from portable particle counters to permanent remote ones,” he says.

“Life sciences regulatory requirements dictate that when product can be exposed, you have to use particle counters within one foot of the activity. We get in very close to filling operations. The particle counters are now easy to swap out. ISO 21501-4 makes them perfectly interchangeable.”

One design goal behind the MET ONE 7000 was to be able to retrofit existing cleanrooms without having to break their integrity. “Everything is built in,” says Smith.

R&D director Szpak says that the MET ONE 7000 instruments include upgrades to the company’s proprietary Core Cal software and changes in its procedure philosophy. That philosophy now encompasses “the calibration process and procedures put in place to meet the intent of ISO, including which tasks are performed by the factory, which are performed by service people, and which by calibrators,” says Phil Ammon, product manager for service. The software and procedure changes differentiate the MET ONE 7000 from the company’s previous particle counters, he says.

Yet all is not lost for earlier instruments already in use. The software provides the means to make the company’s 3400 series particle counters forward compatible. Those instruments can be recalibrated to meet the ISO standard and bring them up to compliance.