Today’s user is often faced with the challenge of meeting several international standards and regulatory guidances as well as performing sampling for airborne particles in a consistent and reproducible manner.

International standards for the monitoring of airborne particles are used by all industries that employ cleanrooms or clean zones. Some form of airborne sampling for particles is needed for these controlled environments in order to assure the quality of the product being manufactured or the success of the process that is being conducted in this controlled or critical environment. Many variables will affect the success of the operations in these areas but the particulate levels in the air are often a significant element in the control of risk, or, inversely, the likelihood of success for the controlled operation.

The initial standard for cleanrooms and clean zones from the United States, known as “Federal Standard 209E,” had a global impact for many years but was officially replaced in 1999 by a new global standard, ISO 14644-1. However, Federal Standard 209E left a legacy of sampling techniques and sample volumes that remain in place today in many applications, such as the focus on sample volumes of 1 cubic foot, sample times of 1 minute in duration and the designation of areas as Class 100, Class 10K, etc. Although some of these methods are still appropriate today, it can be useful to consider some of the changes in standards, regulatory guidances and recommended practices that have occurred since 1999. Some of these address the specific techniques of executing a room classification [ISO 14644-1, EU GMP Annex 1] while others look at the issues of gaining consistency of sampling across the inventory of various particle counters at a user’s site through enhanced on-site calibration techniques [ISO 21501-4, IEST RP-14].

CLASSIFICATION VERSUS MONITORING
One of the most important factors in choosing the right methods, standard, or guidance for an application is the understanding that a sampling method is intended to either a) provide a formal room classification at a moment in time, or b) provide a window throughout a process or procedure in order to contain the momentto- moment risk that airborne contaminants will cause failure or adulteration of that process or procedure.

Formal room classifications executed under the earlier Federal Standard 209E or the current ISO 14644-1 are performed on a 6-month or 12-month basis and give a detailed “snapshot” of the area based on the use of statistical methods. This is in order to gain confidence that the area meets the initial requirements for the process to be performed in the area or zone. Statistics come into play here because the airborne sampling is a representative sampling technique — that is, only a portion of the total air of the room or zone air is extracted from the zone or area small and the concern is that the sampled air will represent the total potential level of suspended airborne particles.