Data-centre cleaning
Dust is in every data centre, and most of it does no harm. The problems come from three kinds of contamination: dust that turns wet and corrosive, conductive zinc whiskers from raised-floor tiles, and sulfur-bearing gases from outside. Each one reaches the UPS as easily as the servers, through the same fans and filters.
Usually not. ASHRAE's white paper on contamination, written by the IT equipment makers on its data-centre committee, starts from the point that most data centres sit in relatively clean environments and that most contamination is benign. It is also frank that dust cannot be kept out entirely: even with the best filtration, dust will be present and will settle on electronic hardware.
What matters is what kind of dust it is and what it does once it has settled. The paper sorts the harm into three groups: mechanical, such as blocked cooling airflow and interference with moving parts; chemical, when settled dust corrodes components or shorts closely spaced features; and electrical, through changes in impedance and bridging between conductors. A UPS is exposed to all three. Its fans move a lot of air, its filters load up, and its boards and busbars carry high voltages close together.
When it gets wet. ASHRAE explains that harmful data-centre dust is generally high in ionic content, such as sulfur- and chlorine-bearing salts, and that it comes mainly from outdoor air. Each type of dust has a deliquescent relative humidity: the humidity at which it absorbs enough water to become wet and conductive. If the room's humidity stays below that point, the dust stays dry and harmless. If the room is more humid, the dust absorbs moisture, degrades the insulation between conductors and can lead to corrosion and ion migration.
Hence the paper's general rule: keep the relative humidity in the data centre below about 60%, which keeps the leakage current from settled fine dust within an acceptable range. Coastal sites deserve a closer look. ASHRAE notes that sea salt can be carried 10 km (6 mi) inland or farther by high winds and can damage electronic devices at that range. Humidity readings are part of server room monitoring, which makes this rule easy to check.
It can, in two ways the paper names. The first is humidifiers that work by evaporating airborne water droplets: if the water feeding them is high in salts, those salts end up as fine dust in the room. ASHRAE's fix is to treat the humidifier water using reverse osmosis.
The second is fibrous dust from paper, cardboard and textiles, which can foul heat sinks and disrupt cooling. The paper's advice is simple and worth making a house rule: new equipment should be unboxed outside the data centre, and high-volume printers should be located elsewhere. For a UPS room this applies to battery deliveries too. Replacement battery blocks arrive in cardboard; unpack them outside the room and bring in only the blocks.
Tiny metal filaments that grow from zinc-coated steel, and ASHRAE calls them the most common electrically conductive particles found in data centres. The undersides of some steel raised-floor tiles are coated with zinc, as are some of the stringers and pedestals that hold them up; electroplated zinc is far more prone to whisker growth than hot-dip galvanized zinc. The whiskers can grow to 1 to 2 mm long. They do no harm while they stay attached, but they come loose when tiles are lifted or underfloor cables are pulled, and are then carried by the airflow into equipment. Circuits above about 25 V can then suffer short circuits, arcing or outright failure.
ASHRAE gives a simple first check: lift a tile, stand it on its edge in a dim area and shine a flashlight across the underside at a 45° angle. Small speckles that twinkle may be whiskers; collecting samples on carbon adhesive tabs for a scanning electron microscope confirms them. If they are present, remediation means replacing the affected tiles and having the data centre cleaned by professionals. This is the strongest reason why a cleaning visit never lifts a whole floor at once; see live-room cleaning.
Gases are the contamination you cannot see or sweep. The paper names sulfur-bearing gases as the most common cause of corrosion on electronic equipment, and explains why measuring the gases directly is not a useful guide. Instead it recommends a simple, low-cost test: expose copper and silver foil coupons in the room for 30 days, then have a laboratory measure the corrosion on them.
The guideline is a copper reactivity rate of less than 300 Å/month and a silver reactivity rate of less than 200 Å/month. Rooms above those rates call for gas-phase filtration of the incoming and recirculated air, which is a cooling and air-handling matter rather than a cleaning one. Cleaning removes settled dust; it does nothing for a room that keeps drawing in corrosive air.
ASHRAE recommends that data centres be kept clean to ISO Class 8 under ISO 14644-1, which it describes as the dominant worldwide standard for classifying air cleanliness by the concentration of airborne particles. For Class 8 the table in the paper gives maximum counts per cubic metre of 3,520,000 particles at the smallest size listed for that class, 832,000 at the next size and 29,300 at the largest.
| Where the air is | Filter ASHRAE gives |
|---|---|
| Room air, recirculated continuously | MERV 8 |
| Air entering the data centre | MERV 11 or MERV 13 |
For rooms without air-side economizers, the paper says Class 8 can generally be reached with those two filter grades alone. In other words, the main defence is filtration, and cleaning keeps what the filters miss from building up. A particle count is the way to know where a room stands before planning any clean.
At the end of the airflow, with the same exposure as the servers and less attention. Eaton warns that dust can block UPS air filters and shut a UPS down on overheating, and asks for the filters to be inspected every month. Schneider Electric's on-line Smart-UPS manual says not to operate the UPS where there is excessive dust or humidity, the same two conditions ASHRAE warns about.
Battery cabinets add their own concern. EnerSys asks for the battery to be observed for cleanliness at regular intervals and for terminals and connectors to be kept free of corrosion, which it notes can affect performance and present a safety hazard. A filter, a fan or a corroded terminal found during a clean is a UPS finding: it belongs in the next UPS maintenance visit, not in the cleaning crew's scope. When a battery string is found corroded, UPS battery service covers testing and replacement.
ASHRAE's general rule is below about 60% relative humidity, which keeps settled dust from absorbing enough moisture to corrode hardware.
Lift a raised-floor tile, stand it on edge in a dim area and shine a flashlight across the underside at a 45° angle. Twinkling speckles may be whiskers; a laboratory confirms them.
MERV 8 on the recirculated room air and MERV 11 or MERV 13 on the air entering the data centre.
With copper and silver coupons left in the room for 30 days and analysed by a laboratory. ASHRAE's guideline is under 300 Å/month for copper and under 200 Å/month for silver.
Yes. Eaton notes that dust can block UPS air filters and shut a UPS down on overheating.
Sources, checked 2026-10-04:
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