Particle counting as part of a Contamination Control Strategy is imperative to maintain an acceptable level of air cleanliness. Clean air is essential in many sensitive environments across a dozen or more industry sectors, be it in manufacturing, R&D or storage applications. In addition, the cleanliness level is often mandated by regulatory requirements, for instance in cleanrooms. 

Cleanrooms are of course a prime example of regulated clean environments. These areas are classified according to the ISO 14644-1 and EU GMP standards that set the permitted concentration of particles by air volume deemed acceptable, depending on what the cleanroom is used for. Grade A or ISO 1 cleanrooms define the top end of the scale. Here, the ISO standard dictates that no more than ten particles of 0.1 microns in size or greater are permitted per cubic metre of air. It is the cleanest classification. Such spaces are typically found in pharmaceutical manufacturing where the fill-finish part of the drug production process takes place in an aseptic (sterile) environment – often a room or special isolator where human access is strictly prohibited.

Some environments need less stringent contamination control. An example is the Grade D or ISO 8 cleanroom status recommended for datacentres to mitigate the build-up of dust, which can impact energy efficiency or even lead to equipment failure where dust impairs the cooling processes of IT systems that can generate considerable heat. This standard allows a maximum airborne concentration of 3,520,000 particles greater than 0.5 microns in size per cubic metre of air. Ambient outdoor air in an urban environment typically contains 35 million particles per square metre, so an ISO 8 cleanroom can be considered ten times cleaner than that.

What counter do you need?

Perhaps the first choice of Airborne Particle Counter (APC) is the physical form factor for your application: handheld, portable or installed in a fixed position. If you’re tracking down a contamination source or testing filters for leaks, a handheld AeroTrak 9303 or AeroTrak 9306 APC is ideal. They offer three or six simultaneous data channels respectively and both detect particles from 0.3 microns to 25 microns in size. Portables can be moved to different locations. Some are very lightweight and easy to move and are proving popular in large cleanrooms. APCs in a fixed location are favoured for continuous environmental monitoring applications and include remote particle counters that operate as part of a facility monitoring system. They typically offer real-time particle count data to enable fast remedial action. But portables can also be installed in a permanent or semi-permanent position to provide a continuous monitoring solution.

Next comes the technical specification of the APC to suit the environment and its classification, the sizes of particles you’ll want to detect and the sampling flow rate. The physical location of the APC in its monitoring environment may also be a factor.

APCs that use standard optical light scattering (a proven and reliable laser technology) offer detection of particles from 0.3 microns to 25 microns in size. More sophisticated APCs, like the AeroTrak 9110 and AeroTrak 7110, extend that detection range down to 0.1 microns. Remote particle counters such as the AeroTrak+ 6000 and AeroTrak+ 7000 Series detect particles down to 0.2 microns in size. The AeroTrak 9001CPC, a highly specialised Condensation Particle Counter (used in super-sensitive Class A cleanroom environments like semiconductor manufacturing), uses pure water to detect particles as small as 10 nanometres.

Finally, the unique BioTrak Real-Time Viable Particle Counter uses conventional light-scattering optical technology for inert particles but also deploys two wavelengths of laser light to induce fluorescence in viable (microbial) particles. So BioTrak gives you a total count for all particles (from 0.5 microns to 25 microns in size) and a separate count for viable particles that present a real contamination threat to patient safety in drug, medicine and medical equipment manufacture.

All APCs in the FMS product range from TSI provide multi-channel monitoring to simultaneously detect particles of different sizes and categorise them accordingly in the count – a process called ‘binning’. Most offer six channels; some APC models offer eight.

 

How to stay ahead of critical contamination events

While periodic monitoring with airborne particle counters lets you detect contamination at the point of use, regular monitoring allows you to build up a pattern of contamination by recording particle measurements and observing trends. Continuous monitoring (see below) does this automatically and is a powerful benefit of a continuous monitoring policy.

A trend of rising measurements can help to prompt an early investigation into likely sources of contamination. APCs can validate the effectiveness of filter systems, while trend analysis can alert to reductions in filter efficiency allowing remedial action to be taken before the cleanroom is compromised by contamination.

 

Why Continuous Monitoring?

It’s now a mandate for manufacturing in the pharmaceutical industry as a directive published in EU GMP Annex 1, which includes continuous monitoring for viable particles (see information on BioTrak). Along with a strong recommendation for the implementation of a documented Contamination Control Strategy (CCS), continuous environmental monitoring must take place to conform to the regulations.

Some cleanrooms check particle counts periodically. Even in sectors other than pharmaceutical, bioprocessing and life sciences that only need to detect inert particles, continuous monitoring is the only way to ensure that stringent cleanroom cleanliness is maintained. Continuous monitoring with APCs featuring real-time particle data allows operators to intervene immediately when counts rise or peak outside the permissible cleanroom standard. Contamination issues can then be quickly identified and resolved to preserve the clean environment integrity.

 

About Sampling Volumes

A key factor in the effectiveness of particle counts is the volume of air the APC instrument samples in a given time. This should be matched to the air volume in the sampled cleanroom or environment and also be based on the expected contamination concentrations. The physical locations of APCs are also a factor in air sampling efficiency. The ISO 14644-1 standard offers guidelines on sampling volumes, locations, etc.

Each APC needs to be able to sample a suitable volume of air to ensure that particles can be detected. Sampling too little air in a lightly contaminated space risks particles continuing to exist but not being drawn into the APC. The converse can be true in expected areas of high contamination with an APC that samples large air volumes. (The AeroTrak+ 6000 Series of remote particle counters includes a built-in vacuum pump to draw air into the APC in locations where no air or vacuum supply exists. They are popular in electronics, semiconductor and industrial applications).

TSI particle counters from FMS commonly feature a flow rate that samples 28.3 litres of air per minute (one cubic foot per minute). The AeroTrak+ A100 Series of portable APCs offers two models (the A100-31 and A100-51) that sample 28.3 litres per minute, two other models (the A100-35 & A100-55) that sample 50 litres per minute (1.77 ft3/min.) and one model (the A100-50) that samples an impressive 100 litres per minute (3.5 ft3/min.)