Which of the following ISO classes would have a higher allowable particle count?

ISO classes are a system of classification used to determine the cleanliness of air in controlled environments such as cleanrooms, where the number of permissible airborne particles varies by class. In this classification system, a lower ISO number signifies a higher level of air cleanliness and a lower allowable particle count.

ISO Class 8 is the correct answer because it has the highest allowable particle count among the options provided. Specifically, ISO Class 8 allows for a higher number of particles per cubic meter in various size ranges when compared to ISO Class 5, ISO Class 6, and ISO Class 7, all of which have stricter limits on particle counts.

For example, ISO Class 5 allows a maximum of 3,520 particles per cubic meter for particles larger than 0.5 micrometers, whereas ISO Class 8 permits a significantly larger number. This difference is crucial for environments where sterility and low levels of airborne contaminants are essential, such as in pharmaceutical compounding or operating rooms. In contrast, as the ISO classes increase numerically, the cleanliness decreases, allowing for more particles in the air, which is why ISO Class 8 stands out with its higher permissible particle count.