Data centre contamination and ISO 14644 cleanliness
ASHRAE says data centres must be kept clean to Class 8 of ISO 14644-1 [1], an air cleanliness class taken from the cleanroom standard. The particle that does the most harm is the zinc whisker: ASHRAE calls it the most common electrically conductive particle in data centres [2]. Construction dust, outside air and worn filters supply the rest.
Key facts
Zinc whiskers
Some steel raised-floor tiles are coated with zinc on their undersides to prevent corrosion, and whiskers grow from that coating [2]. They stay put until someone lifts a tile for cabling work. Then the cooling airflow under the floor carries them to the equipment inlets. Once inside IT equipment, they can cause short circuits, arcing, signal problems or outright failure in circuits running above about 25 V [2].
Signs that a room has them:
- A fuzzy, glinting coating on the underside of a tile under a flashlight held at a low angle
- Unexplained power supply failures clustered near recently lifted tiles
- Failures that follow cabling work under the floor
Where the rest comes from
| Source | How it gets in | What stops it |
|---|---|---|
| Fit-outs and renovations | Drywall, concrete and drilling dust | Sealing off the work area; a clean after the work, never before |
| Outside air | Economisers and make-up air | Filters changed on schedule |
| Cooling units | Worn filters and belts shedding debris | Filter and belt checks at each cooling visit |
| Packaging | Unpacking equipment inside the white space | Unpacking in a staging area |
Why the UPS cares
UPS modules pull room air across their heat sinks and boards with their own fans. Dust on those surfaces raises their temperature, and conductive dust creates leakage paths. Vertiv’s APM2 manual asks for its air filters to be cleaned or replaced every two months, more often in dusty rooms [3]. A room that clogs filters faster than that is telling you its cleanliness has slipped.
Measuring it
ISO 14644-1 classes are particle-count limits [1], so the check is a particle count: readings at set points above the floor and in the plenum, before and after a clean. The data-centre cleaning service records counts or photos at each visit, so the trend shows whether the cleaning interval is right.
Standards cited
- ASHRAE Gaseous and Particulate Contamination Guidelines for Data Centers
- ISO 14644-1 (as cited by ASHRAE)
Common questions
What cleanliness class should a data centre meet?
Class 8 of ISO 14644-1, the level ASHRAE says data centres must be kept to [1].
What are zinc whiskers?
Microscopic conductive filaments that grow on zinc-coated steel, including the undersides of some raised-floor tiles. ASHRAE names them the most common conductive particles in data centres [2].
How often should a data centre be cleaned?
On a schedule set by particle counts and the room's history, and always after construction or major cabling work.
Can contamination damage a UPS?
Yes. UPS modules draw room air through their electronics, so conductive dust can short circuits running above about 25 V [2], and ordinary dust makes them run hot.
Sources
- ASHRAE TC 9.9, 2011 Gaseous and Particulate Contamination Guidelines for Data Centers, Table 4
- ASHRAE TC 9.9, 2011 Gaseous and Particulate Contamination Guidelines for Data Centers, Particulate contamination section
- Vertiv, Liebert APM2 UL Modular UPS User Manual SL-71948, printed p. 156 (PDF p. 164)
Updated