Understanding cleanroom classification and monitoring is critical to production and compliance. To prevent confusion between these two definitions, Hasim Solmaz, Lighthouse Worldwide Solutions, describes common and different points
Imagine you are getting ready for your birthday party. You wear your best clothes, visit a hairstylist and be charming as ever! This is what we called “classification” in the cleanroom world: you know that in 10 minutes your particle counter will start and you will have your results for the next six to 12 months. No one wants to fail right? So, clean the “mess”, double check your surface cleanliness, HVAC, return grills and remove unnecessary items.
But, what if someone knocks on your door to deliver a gift early in the morning right after your very late birthday celebration night? Even while you are still sleeping? Can you imagine! You are in pyjamas with messy hair! This is what we called “monitoring”: you fully focus on your production routine, but there are also several contributors to your production quality, especially viable and non-viable contamination aspects. Under these circumstances, you should have your particle levels within the acceptable level without knowing what is waiting for you in your production routine.
Based on this analogy, you cannot wait until the early morning with your best clothes and hair for a potential visitor, but at least you can be ready for any of your friends to visit early morning. In the sterile manufacturing world, we should be prepared for any unexpected situation, and that’s why we have monitoring systems. They are like our camera and infrared sensor reminding us as early as possible to get ready for these “unexpected guests”.
Let’s start with classification (the birthday party) to get a better understanding.
Cleanroom classification
As mentioned in various standards and regulations, such as EU GMP Annex 1 and the US FDA Aseptic Processing Guideline, cleanroom classification as per ISO 14644-1 is essential for continuous compliance. Cleanrooms and clean air devices should be classified following ISO 14644-1. Classification should be clearly differentiated from operational process environmental monitoring. Portable particle counters are used for cleanroom classification.
Now, consider the following example of classification calculation: A cleanroom has a floor area of 30sqm and is specified to be ISO Class 5 in operation. The classification is to be performed using a discrete particle counter having a flow rate of 28.3 litre per minute. One particle size will be considered: D1 ≥ 0.5 μm
Now, define parameters from table, equation and known data. First, write down all known data:
- Room Area ► 30sqm
- Targeted Class (N)► 5
- Particle counter flow rate ► 28.3 LPM (1 CFM)
- Particle Sizes Considered ► D1=0.5 μm
Now, let’s get data from tables;
NL = 7 locations, (As per Table A.1)
Cn,m (≥ 0,5 μm) = 3520 particles/m3 (As per Table 1)
Table 1
Second, calculate minimum single simple volume, Vs ;
Vs=(20/(Cn,m))×1000
Cn,m (≥ 0,5 μm) ► Vs=(20/3520)×1000=5.68 litres
The single sample volume has been calculated to be 5.68 litres. As the light scattered airborne particle counter (LSAPC) being used for this test had a flow rate of 28.3 litres per minute, a minimum 1-minute single sample count would be required, and therefore 28.3 litres would be sampled for each single sample volume.
Reporting: Prepare sampling data table for 0.5 μm particle size
For this example, single particle size 0.5 μm is considered. However, more than one particle size suitable for targeted ISO Class mentioned in Table 1 (ISO 14644-1:2015) can be selected.
In this case, the same sampling data table should be prepared. Each line in all tables should pass to achieve targeted ISO Class.
For the same sampling location, an additional sample can be measured, and the average can be calculated.
In many cases, undesired interventions such as isoprobe/tubing contact, at rest condition interruptions, or as per sampling plan etc., can lead to multiple single sample volume.
If multiple single sample volumes are taken at a sampling location, the concentrations are averaged and the average concentration must not exceed the concentration limits given for the specified ISO Class targeted.
Here, 35.3 is the multiplier to reach 1000 litres as per particle counter flow rate, which is 28.3 LPM (35.3 x 28.3 = 1000 litres). For 50 LPM particle counters, this multiplier will be 20 and for 100 LPM devices, 10.
At location 4, one of the individual particle count concentrations does not meet the limit established in Table 1; however, the average particle concentration for location 4 does meet the limit.
The average particle concentration for each of the sampling locations does meet the limit established by application of calculation table. Therefore, the air cleanliness by particle concentration of the cleanroom meets the required ISO Class.
Table 2:
a. All concentrations in the table are cumulative, e.g. for ISO Class 5,
the 10200 particles shown at 0.3 μm include all particles equal to and greater than this size.
b. These concentrations will lead to large air sample volumes for classification.
Sequential sampling procedure may be applied; see Annex D in ISO 14644-1:2015
c. Concentration limits are not applicable in this region of the table due to very high particle concentration.
d. Sampling and statistical limitations for particles in low concentrations make classification inappropriate.
e. Sample collection limitations for both particles in low concentrations and sizes greater than 1 μm make classification at this particle size inappropriate, due to potential particle losses in the sampling system
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