ISO 14644-1 Class 8, Explained for Data Center Managers

ISO 14644-1 is the international standard for classifying how clean the air in a room is. It was written for cleanrooms, but equipment makers and the ASHRAE TC 9.9 guidelines borrow it as the yardstick for data centers, because it gives everyone the same numbers to talk about.

What the classes mean

Each class sets a maximum number of airborne particles per cubic metre of air, at several particle sizes. The lower the class number, the cleaner the room. Class 8 allows, per cubic metre:

• up to 3,520,000 particles of 0.5 µm and larger
• up to 832,000 particles of 1 µm and larger
• up to 29,300 particles of 5 µm and larger

For comparison, a human hair is roughly 50 to 100 µm across. The particles that matter here are invisible, which is exactly why they have to be counted rather than judged by eye.

Why Class 8 for data centers

Many hardware makers state in their environmental requirements that a data center should be kept at ISO 14644-1 Class 8 or cleaner. Fine dust settles on heat sinks and in fans, reduces cooling, and — combined with humidity — some particles can absorb moisture and become conductive or corrosive.

How a particle count works

• A calibrated laser particle counter draws in a known volume of air and counts particles in size channels such as 0.3, 0.5, 1.0 and 5.0 µm.
• The standard sets the minimum number of sample locations from the floor area of the room.
• Samples are taken at working height, spread across the space.
• The results are compared with the class limits and reported, location by location.