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 (15â€™ X 18â€™), 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
|Class||0.1 Âµm||0.2 Âµm||0.3 Âµm||0.5 Âµm||1 Âµm||5 Âµm|
Notes: Number of particles per cubic meter (m 3 )
Q. – I would like to assess the air change rate â€“ which I think is â€œAirflow Volumeâ€™ or perhaps â€˜Airflow Velocityâ€™? 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 â€˜clean zonesâ€™ 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:
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