Qualification of an Environmental Monitoring Program - 1. Selection/Justification of Sample Sites   

N_L is the minimum number of sampling locations (rounded up to a whole number); and

A is the area of the clean room or zone in meters²

This might work well enough for non-viable particulate measures (which, after all is the intent and scope of 14644-1) but we also wish to consider viable air sampling (both passive and active), and viable surface monitoring.   Let’s make this a bit easier and argue that both viable and non-viable active air sampling sites should be done at the same location (or as close as practical to avoid compromising the other measure, or the integrity of the product).  Therefore the number of active air sampling sites is driven by the non-viable particulate calculation.  

Passive air sampling (settle plates), are a frequently-used measure of clean room (or zone) control.  They have the several advantages in this regard, chief among them the ability to remain in continuous exposure for up to 4 hours (exposure time must be demonstrated) and they are not disruptive to the immediate environment and so may possibly sample sites very near product exposure points (see Whyte, 1996 for a discussion of these, and other , advantages).  In addition, they are not as prone to variation among different vendors as are active samplers (Yao and Mainelis 2006).  However, it is not clear how to interpret the data in all cases from areas of laminar air flow at the rates used for modern clean rooms.     However you view their usefulness, the current international regulatory expectation for air monitoring includes their use and the justification of sampling sites.  A prudent measure is to use the same number of sampling sites for settle plates as used for the active viable and non-viable sampling programs.  These will not be the same sites, but similar in number.

Remember, we are not talking about the sample sites for the on-going environmental monitoring program, but rather the qualification of the sample sites to be used in that routine program.

This leaves us with determination of the number of surface sampling sites for the qualification study. There is no regulatory guidance directed to this point for the international pharmaceutical industry (even PIC/S, which generally can be counted on to provide details on almost everything microbiological, is silent on this point – PIC/S 2004). Also silent on this point is the PDA (Parenteral Drug Association) Technical Report #13. We are left to our own devices. One approach to determination of the number of sites would be to address it in an manner similar to that of ISO 14644-1 for the walls and floors (as relevant). Each surface would then be treated as a separate item and the minimum number of sites determined for each as the square root of its surface area.

This leaves us with only the question of how to determine the number of surface sampling sites for equipment. This cannot be answered by this approach convincingly (in my opinion). This determination, quite frankly, may well be something that must be left to each facility as the numbers could be driven by the nature of the equipment and as well as the associated manufacturing process.

Having determined the number of sites for each room, we now need to determine their location.

Selection of Sample Sites

• At which sites would microbial contamination most likely have an adverse effect on product quality?

• What sites would most likely demonstrate heaviest microbial proliferation during actual production?

• Should site selection involve a statistical design (e.g.,following the calculations in Federal Standard 209E) or should site selection be made on the basis of grid profiling? Should some sites for routine monitoring be rotated?  [Note from author:  As 209e has been withdrawn in favor of ISO 14644, the answer is No]

• What sites would represent the most inaccessible or difficult areas to clean, sanitize, or disinfect?

• What activities in the area contribute to the spread of contamination?

• Would the act of sampling at a given site disturb the environment sufficiently to cause erroneous data to be collected or contaminate product?” 

The FDA Aseptic Processing Guidance document (FDA 2004) also provides some guidance in section IVA:

“Air in the immediate proximity of exposed sterilized containers/closures and filling/ closing operations would be of appropriate particle quality when it has a per-cubic-meter particle count of no more than 3520 in a size range of 0.5 μm and larger when counted at representative locations normally not more than 1 foot away from the work site, within the airflow, and during filling/closing operations. This level of air cleanliness is also known as Class 100 (ISO 5).  

We recommend that measurements to confirm air cleanliness in critical areas be taken at sites where there is most potential risk to the exposed sterilized product, containers, and closures. The particle counting probe should be placed in an orientation demonstrated to obtain a meaningful sample. Regular monitoring (Continued from page 3) should be performed during each production shift. We recommend conducting nonviable particle monitoring with a remote counting system. These systems are capable of collecting more comprehensive data and are generally less invasive than portable particle counters. See Section X.E. for additional guidance on particle monitoring.

Some operations can generate high levels of product (e.g., powder) particles that, by their nature, do not pose a risk of product contamination. It may not, in these cases, be feasible to measure air quality within the one-foot distance and still differentiate background levels of particles from air contaminants. In these instances, air can be sampled in a manner that, to the extent possible, characterizes the true level of extrinsic particle contamination to which the product is exposed. Initial qualification of the area under dynamic conditions without the actual filling function provides some baseline information on the non-product particle generation of the operation.”