Particle Count Size

why we do not measure particles below
0.5 micron during area qualification?

Most commonly bacteria size is in between 0.5 to 5.0 micron and bacteria less likely attach to non viable particle size smaller than 0.5 micron so particle size smaller than 0.5 is not critical issue.particle size greater than 5.0 micron is not good carrier for bacteria because it settles down easily due to heavy weight.

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if we consider non viable count then why not leess than 0.5 um?

bacteria less likely attach to non viable particle size smaller than 0.5 micron so particle size smaller than 0.5 is not critical for microbial contamination.

particles less than 0.5 may not b contaminants ?
apart from microbial growth…

Viable is more harmful than non viable.particle size less than 0.5 is source of contamination but it is tolerable in human body.

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Bacteria have a diameter between 0.3 and 20 microns, for this reason, HEPA filter has a pore size of 0.3 micron… So why are we looking for a 0.5 micron particle???

The above answers were not convincing…

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We need to measure 0.5 size particles because of our human body blood capillaries having the 0.5 u dia, it may obstruct the blood flow and damage the tissues,when it goes into blood stream.
It is one of the reason to measure that particular size …

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A capillary is a small blood vessel from 5 to 10 micrometres (µm) in diameter, and having a wall one endothelial cell thick. They are the smallest blood vessels in the body: they convey blood between the arterioles and it is wrong to say that blood capillaries have size of 0.5 micron.

Yes you are correct… capillary size is 5u only not 0.5, but my aspect is we have to measure maximum size I.e 5u.Bcz of the reason is above what said previously.

We are looking for 0.5micron because the PAO (Poly alpha Olifine) test is a filter integrity test the identification of greater partical size will show failure of Hepa or Ulpha filter

. The size of PAO generated aerosol ranges from 0.1 to 1.0 μm.
The PAO aerosols are generated by the aerosol generator and passed through the HEPA filter then the integrity is checked using a photometer. 99.97% particles having a size larger than 0.3 μm should not be passed through HEPA filters.

The effects of particle size on vascular walls in cardiovascular diseases:
When the WSR (vascular Wall Shear Rate) was increased, the adhesion increased only when the particle size increased from 0.5 up to 5 μm.

To link to this article:
DOI: 10.1080/17425247.2017.1316262


What are you thinking about this article?

Maybe this article does not help us, but be sure your answer is in the following:

• ISO 14644-1:2015 focuses on ≥0.1μm, ≥0.2μm, ≥0.3μm, ≥0.5μm, ≥1.0μm and ≥5.0μm particle sizes
• FDA Aseptic guidelines: 0.5μm only
• EU focuses on 0.5 and 5.0μm particle sizes
…Each authority has its own criteria.

Consider that, USP <788>: particulate matter in injections - Particles counting for 10 and 25μm sizes…!


The FDA emphasise in the Guide to Aseptic Filling that the 0.5 micron size is te important one for determining if the environment is below or above the accepted evel of particles and in doing so draws upon the ISO 14644 cleanroom standard. However, more controversially with Europe, the EU GMP Guide states that both particle sizes are important.

In arguing against the need to measure 5.0 microns, Gail states:

EC GMP requiring the detection of 5-µm particles with a sample volume of at least 1 m³ for ISO Class 5 classification and monitoring, overlooks some essential facts:

  • 5-µm particle counts in an ISO Class 5 environment should be avoided in principle due to background noise level and poor resolution. The poor reliability of 5-µm particle counts cannot be fully compensated by increasing the measuring time.
  • 5-µm particle determination proves to be about 10 times more expensive and timeconsuming than 0.5-µm particle counts.
  • Currently there is no scientific evidence that 5-µm particle detection offers any improvement for cleanroom hygiene control. EC GMP regulation impedes international harmonization of cleanroom qualification and monitoring procedures.

Even with the latest development of particle counters that offer substantially higher sampling flow rates, the situation does not improve: Areas of ISO Class 5 normally are as small as possible. A particle counter with high sample flow rates cannot be placed in that area since the high sample flow is withdrawn from a small volume. In small areas such as pass-throughs, when the sample flow air is returned into the environment, the pressure differential may be affected; when the sample flow air is returned into the measured area, the air change rate may be affected.