Clause 5.9 does not take into account that at 0.5 micron measurements tube length and bends is less important than at 5 microns! This brings us right back to notes d) and e) in Table 1 of ISO 124644-1:2015. During routine monitoring trending is the most important consideration and therefore you have more wriggle room in terms of justification of longer tube lengths and more bends due to configuration challenges, than you have during Classification. Now for the longer version, if we want to better understand the underlying issues involved. We need to take a deeper dive into the detail and go back to the basics and the challenge of measuring microbiological contamination and assessing the risks in the cleanroom environment to product quality and ultimately patient safety. This arises because we have the common use of laser airborne particle counters (LSAPC) that give real-time instantaneous results after 1 minute, but of the total number of particles, with no discrimination between inert and microbiologically active particles or micro- organisms. LSAPCs have been used for cleanroom classification for decades but have some limitations at larger particle sizes, when remotely used, e.g. in ISO 5 UDAF RABS and Isolator Life Science applications. Until the advent of BFPCs (BioFluorescent Particle Counters) we relied on traditional indirect sampling based methods using CFUs (Colony Forming Units) rather than AFUs (Auto Fluorescing Units). Unfortunately CFU based
methods rely on growth and take multiples of days to show evidence of microbiological presence. This is why microbiological contamination is commonly referred to as the “Unseen Enemy” or “Bad Bugs”. In the absence of real-time viable particle counters conventional wisdom in Europe was look carefully at 5 micron and greater particle sizes as they reflected micro-organisms or microbe carrying particles (typically around the 25 micron size). Although there is no clear explanation or history, critical cleanroom regulatory guidance are different in the US and the European Union (EU). Requirements for cleanrooms are among the most critical issues of Good Manufacturing Practices (GMPs), but differences between expert opinions among regulators in the US and EU are responsible for this difference, creating confusion and misunderstandings. In the US the concentration is on 0.5 micron particles but in Europe the requirement was to measure at both 0.5 and 5 micron particle sizes.
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