Recently, a Controlled Environments reader contacted me asking for help with a cleanroom-related question:
“We have a Class 10,000 cleanroom. My question is, when can one enter the cleanroom after starting an AHU [air handling unit]? Meaning, after how much time? Is there a standard governing, and what is the rationale or justification for the answer?”
I posted the inquiry to Controlled Environments’ social media channels, and several members of the CE LinkedIn group came through with answers. Here’s what they had to say:
- Anytime AHU is off, you might be getting inflow from outside air or corridors, etc. … so if for any period, you may need to do wipe-downs etc. Is this pharma or aerospace, optics or other app. Ideally, never turn the air handler off. You might want to assess not just air particle counts, but surface counts using QIII or black swabs and then clean surfaces using clean wipes.
- We would need to know more about the application, about potential sources of contamination, and about why AHU was turned off in the first place (and for how long). It might be necessary to look at chemical contamination both in the air and on surfaces.
- If [the] HVAC is “turned off,” then one would expect all critical product and work surfaces to be protected/covered, avoiding the necessity for any “heroics.” Continuous airborne particle monitoring, if deployed properly at the critical product/work surfaces of interest, would verify minimal recovery efforts, if any, to be required.
- It’s a difficult question to answer simply. I would need to understand why the AHU was turned off? If the room is left stagnant without air exchanges for any period of time, I would recommend a micro-cleaning of the room prior to starting up any process in that environment. There are recovery calculations that can be applied if you have a need to continuously shut your room down. Ultimately, your room should be operational at all times — even during non-working hours. There are energy saving options that can implement, that will allow you to lower the air change rates while keeping within safe particle limits, if that’s of interest.
- Covering things during a dirty operation like drilling, etc., is good idea, but covering all surfaces in not easy, and what covering do you use? The cover will collect contamination on surface but hard to pull off cover when done without releasing at least many of larger particles, so will help some, but cleaning with wipes still may be needed post removing any cover. Class 10,000 is not the most critical cleanrooms, so [there is] some leeway … but for cleaner cleanrooms, I recommend wiping down all critical surfaces or surface above or upwind after any significant duration HEPA’s off period. If you have a surface spec based on QIII for surface particles or microbiological spec, the proof is in testing to assess what can be tolerated. Why was HVAC/HEPAs off and for how long, in this case?
- Covering can be performed, e.g., with verified clean packaging material or with dedicated clean covers — think “cake dish cover.” Proper removal is a technique that can be imparted through training. In ANY cleanroom, surfaces just get dirtier slower … performing a “wipe down,” without any data to support the need, may actually place product at more risk. Regular cleanroom cleaning is assumed, but if the cleanroom is being “turned off” maybe cleaning is not happening either?
- I think what is important to understand here is the reason why they need to turn it off. Temporarily? Overnight? For production campaign pause? If the needs of a cleanroom HVAC shut down is related to power saving initiatives, then I would suggest applying a different approach such as air speed reduction instead. This will maintain the cleanroom over pressurized and will not allow contamination to enter from uncontrolled areas, helping your company in saving energy without spending additional money for the necessary check after the HVAC system re start.
Thank you, readers!