Zinc whiskers, although a catastrophic problem, are not new (they were discovered in 1948 by Bell Labs). They grow on many zinc coated components and structures commonly used in Data Centers. Zinc coating is used to slow the rusting of steel components. There are two types of zinc coating, Hot Dipped Galvanized (HDG) or electroplated. Only one type grows whiskers!
Look for zinc coatings on the underside of floor tiles, metal supporting struts and tile frameworks as well as in air handling equipment, ducting and vents.
Zinc whiskers can cause chaos in a data center as these fine growths can be carried by the airflow into computer equipment causing short circuits and intermittent or permanent system failures.
- The HDG coating does not cause zinc whiskers and can be easily recognized by an irregular triangular or spangled pattern on the metal surface.
- Electroplating does cause zinc whiskers and can be recognized by having a dull and uniform gray surface. (To make it more complex, in some cases additives may have been used in the electroplating process, resulting in a bright shiny appearance).
If you suspect that you have zinc whiskers be very careful when moving floor panels. Rough handling will dislodge whiskers and exacerbate the problem. Remove a panel and take it into a darkened room, use a very high intensity flashlight, point the beam at the coated surface at an acute angle. Look for sparkling or twinkling on the surface. If you get this, it is very likely that you have the problem.
Zinc whiskers grow from electroplated surfaces on their own (spontaneous growth). Whiskers grow faster when the surface is under load or compression (compression growth) such as on floor tiles or struts. Spontaneous growth occurs on electroplated tin, zinc and cadmium. Although tin and cadmium electroplating is rarer in the fabric of our Data Centers it is still quite common inside computer equipment itself.
Electroplated material viewed under an electron microscope is laid out in a lattice pattern. Over time, the atomic structure begins to separate pushing the coating away from the steel surface. Whisker growth occurs from the base like toothpaste from a tube. This breakdown process is known as atom migration.
The whiskers grow at a rate of about 250 microns per year and have a uniform diameter of about 2 microns. The whiskers can reach lengths of up to 1 cm (0.4 inches). The whiskers become a significant contamination risk after two years when they reach a length of 500 microns (0.5 mm or approximately 1/64 inch). As the whiskers grow, they eventually break off and spread throughout the data center, following airflow patterns. Breakages can be caused by rough handling, vibration from moving equipment around as well as fast moving airflow. The longer (older) the whiskers are, the more likely they are to break off.
Zinc whiskers will settle inside any air cooled equipment and on any surface including Servers, Storage, Network Equipment PDUs and Power Supplies. Zinc conducts electricity and can cause short circuits in low voltage electronic equipment. It is unlikely to cause problems or damage to high voltage, high current systems.
Airborne zinc has the possibility of causing poor data center air quality resulting in an Occupational Health & Safety hazard (checkout airborne toxic metals to learn more about the dangers).
There are two main ways to independently and absolutely confirm the presence of zinc whiskers, electron microscope photos and chemical analysis (lower cost). Your test results will indicate if zinc whisker remediation is necessary. Use a specialist and local firm to perform the checks.
If you do have zinc whiskers, make sure that floor panel handling is minimized and that when essential it is done gently. Contaminated tiles left undisturbed will not shed many whiskers, rough handling will cause catastrophic problems.
The only remediation solution that works in the long term is complete removal of all of the panels, followed by a thorough deep clean. Some firms may suggest painting over the zinc coating, but this only works in the short term as whiskers will continue to grow through the paint. Contract a specialist that has done this type of work before, carries the correct insurances, has the proper equipment and can give good references.
Replacing floor tiles and other load carrying components is non trivial and should only be attempted with extreme care. Specialist lifting gear is required as is a huge amount of labor and skill. Data Center move skills are essential to negotiate and manage outages as equipment is moved to allow tiles to be replaced.
I would be delighted to hear from anyone who can recommend specialist firms in this area.
Comment by Peter Curran on 1 June 2008:
Steve
We used a firm called Data Clean (http://www.datacleaneurope.co.uk) based in the UK who did a pretty good job for us. Not sure if they travel further afield?
Good article by the way, I wish it was around when we were suffering from the original problem.
Pete
Comment by Steve O'Donnell on 1 June 2008:
Thanks Pete,
It is great to get some real live recommendations from someone who has suffered with the problem.
Any more specialists that folks have used?
Steve
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