Which ISO class has a lower maximum particle count for particles of 0.5 µm and larger?

The correct choice indicates ISO Class 7 as having a lower maximum particle count for particles measuring 0.5 µm and larger. ISO classes are part of the ISO 14644-1 standard, which categorizes cleanroom environments based on the maximum allowable levels of airborne particles.

For ISO Class 7, the maximum allowable particle count for particles of 0.5 µm and larger is set at 3,520 particles per cubic meter. This means that environments classified under ISO Class 7 are permitted to have fewer particles compared to those of classes with higher numbers.

In contrast, as you move to higher ISO class numbers, such as Class 8, 9, or others, the permitted number of particles increases, leading to a less stringent particle level. To maintain strict control over particulate contamination, particularly in settings like pharmaceutical manufacturing or healthcare, adhering to classifications like ISO Class 7 is vital for ensuring a safer environment for processes involving sterile products or sensitive operations.

Understanding these classifications is crucial for professionals working in environments where cleanliness and sterility are of utmost importance, thereby making ISO Class 7 the correct answer in this context.