BLOG FAQ’s: Non Viable Particle Recovery Verification After a Power Outage

BLOG FAQ’s: Non Viable Particle Recovery Verification After a Power Outage

Question: “What is the need of taking a non-viable particle count after a power shut down for an hour. Our Class C area is stabilizing after 30 minutes of a power cut?”

There are several reasons for deploying your Non-Viable Environmental Monitoring Program following a power outage, but primarily it is to ensure that the HVAC has been restored and is now operating optimally – this is the 30-minute stabilization that you witness in your Grade C areas. Grade C areas have a relatively high air exchange rate (nominally, 20 air volumes per hour) so stabilization will occur rapidly in the unmanned state.

Taking that one step further, to ensure that the system is fully restored, it should also be challenged in the manned state. Stagnant air during the power loss may have resulted in sedimentation of particles and operator movements may stir these up. It’s important to demonstrate that these re-entrained particles have also returned to levels where they do not pose a risk.

EC GMP guidance currently requires that the at-rest state should be achieved after a short “clean up” period of 15 to 20-minutes, and the post-event monitoring results of the Grade C and D areas should also reflect the same clean-up period. This is again an adjustment from manned to unmanned/at-rest, and not completely back into operation.

The language of the revision to EU GMP Annex 1 requires that a room be requalified to ensure that conditions are restored. The conditions that drive that activity are:

  1. Change in use of the cleanroom
  2. Interruption of air movement which affects operation of the cleanroom
  3. Special maintenance

It may be the effects of item (2) that are driving your need to requalify the room, and this requalification exercise takes the hour you are referencing to complete. (Note that it is satisfactorily well beyond the 15-20 minute recommended “clean up” period). Of course, it is still important to perform additional microbial sampling following the restart, but the particle counts are more informative at this point in the area’s recovery because they are instantaneous.

The adoption of a Contamination Control Strategy, where your product risks are clearly and comprehensively identified and the ramifications of potential contamination understood, should be incorporated into your restart procedure. This may also be useful in shortening the delay to restart, especially if ‘brown-outs’ of power are all too regular in your facility’s geographical location.

We receive many questions from our website regarding suitable or “best” practices for particular applications. Please continue to send your questions to  If you’re asking the questions, there are no doubt others in the industry who are wondering the same things, and we’d like to share your FAQ’s in upcoming blogs.




Mark Hallworth

Life Sciences Global Manager and Sr. GMP Scientist, Particle Measuring Systems

Mark Hallworth is the Life Sciences Strategic Senior GMP Scientist. Mark has managed the design, installation and validation of over 200 environmental monitoring system projects worldwide. He has designed several products specific for pharmaceutical environmental monitoring, including particle counters for explosive and corrosive areas and 21 CFR part 11 compliant software for batch test and release. He currently lectures for the PDA, ISPE and other international pharmaceutical societies on environmental monitoring and GMP compliance design and validation. Mark has written over 100 technical papers on environmental monitoring and contributed to several books specific to this field, he was awarded the IEST James Mildon award for “significant contributions to the advancement and increase of knowledge in the field of contamination control”.

Additional Resources:

Cleanroom Classification, Qualification, Monitoring

Three Core Events to Establish Environmental Contamination Control – Per EU GMP Annex 1

Build the Ideal Contamination Control Strategy

Highlights of the New Lasair Pro Airborne Particle Counter

The Antibacterial MiniCapt® Mobile – For Best-in-Class Microbial Contamination Monitoring

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