I recently had a customer ask us some questions about certifying and testing two cleanzone tents in which he wants to validate to ISO 14644 class 8. As he did not have prior experience validating to ISO 14644 standards, he purchased the ISO 14644-1 and ISO 14644-2 books from the IEST. As with most people the first time through, he has struggled to understand exactly what he needs to do in order to validate. Below is a question and answer session that transpired between the customer, myself and Jim Akey from LWS.

Q. – Based on the area (in meters) of each room (15’ X 18’), the minimum sample point locations is 5 per room. Using a DPC to determine room particle counts, a sample volume is needed. Based on ISO 14644-1:1999(E) Annex D, and an ISO Class 8 requirement, Cn is very large, and Vs is small (less then 2 liters). Do I just take 28 liters over 1 minute as a standard? Why? If not, how do I determine the sample volume?

A. – This is a two part answer:

1. Sample Locations – 14644 states that to determine the minimum number of Sample Locations (B.4.1.1) you take the square root of the Area (in m2). If the room is 15′ x 18′, this equates to 25.08382 square meters. The Square Root of 25.08382 (room area) = 5.0083749 (sample locations).

ISO 14644 states that you must round up, so 5.0083749 = 6 Locations.

Q. – How is the number of particles per cubic meter calculated (ISO 14644-1:1999(E) Annex D.1.7)? I need the number of particles per cubic meter to calculate the 95% upper confidence limits since the number of sampling locations is less then 10.

A. – The easiest way to see if you are within classification is to compare the particle counts to the chart (Table 1) in the ISO standard. There is a formula to determine this – Section 3.2 of ISO 14644-1

ISO 14644-1 Cleanroom Standards

Q. – I would like to assess the air change rate – which I think is “Airflow Volume’ or perhaps ‘Airflow Velocity’? According to ISO 14644-3:2000(E), I think I would reference Annex B.4 Airflow test? What minimum air change rate should I use as the acceptance criteria? I have heard 6 to 20/hour, but have not seen the number in print any where. Is there a formula? Can you provide me a reference? Is Airflow Velocity the same as Airflow Volume?

A. – Air Velocity is not addressed in sections one or two. I would suggest you purchase the ISO 14644-3 standard which specifies test methods for characterizing the performance of cleanrooms and clean zones. If you are only interested in calculating air exchanges per hour, the formula is very simple. Calculate total volume of air (cubic feet) by multiplying length, width and height of the room. The resulting number is your volume of air in cubic feet. Divide your cubic footage by 60, the resulting number is the amount of cubic feet per minute required for one complete air exchange. Divide this number into the amount of CFM your air handler is delivering, the resulting number is your air exchanges per hour!

L X W X H = Cf
Cf/60 = X
CFM/X = air exchanges per hour
Q. – I am also proposing to perform:

a. A filter leakage test to verify filter integrity;
b. Airflow direction test and visualization (in the operational state only) to verify the required airflow pattern; and
c. Containment leakage to verify non-cross contamination.

Are all three of these tests applicable to the ‘clean zones’ we have, and is this overkill for ISO Class 8?

I hope that if anyone else has these types of issues, this blog will help provide some direction. If you have other questions or comments about validating and testing to ISO 14644 standards, we are available to answer your questions. There are 3 ways you can get assistance:

1. Click on the comments button below and ask your question(s)
2. email info@particlecounters.org
3. call toll free 1-800-531-4889

I recently spoke with a woman named Becky from 3M who had a lot of questions about the Lighthouse 3016 handheld particle counter. She is looking for a particle counter that can count particles from .3 microns up to 25 microns. I explained that the Lighthouse 3016 could be upgraded to include the 25 micron size for a minimal charge. After answering many of her questions, she asked one I had not heard in a while:

"While looking at the technical specs, I notice that for counting efficiency, it says 50% per JIS… what does that mean?"

I remember asking the same question several years ago, the specification seemed to imply that the unit was only doing half of it’s job. Could this be correct???

The fact is that it is the way particle counters are designed and calibrated. The lowest particle size is always 50% counting efficiency. Lets say we are calibrating the 0.3 micron size – as you run the particles through the sensor, we are looking at the reflected light from each particle. As all 0.3 micron particles are not exactly 0.3 microns (some are 0.2999, and some may 0.3001, etc), you get a bell curve. As you need to have a cut-off point, you select the middle of the "curve" (or the 50% area), and call that 0.3 microns. In reality, the counter is counting all of the 0.3 microns partilces. It’s more of a term than actually describing the efficiency of the counter. This confuses MANY people!!

I was speaking with Jack, a gentleman from Florida, who was asking me about how to convert particle counts to particle mass (ug/m3). He had also asked if there were guidlines for particle limits in residential settings. He has posted his question in the comments section of this blog. Jim Akey from Lighthouse Worldwide Solutions jumped in to answer the questions and offered Jack some great resources on the topic.
Click on the “comments” link below to read the question and response from Jim Akey and/or join in the discussion.

Questions are usually answered within 1-2 days. If you need further assistance, please call toll free 1-800-531-4889