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Are Your Whiskers Going To Crash Your Computer?
If you think zinc whiskers are what happens when the tin man forgets to shave - guess again. Zinc whiskers are real and they could be growing right inside your computer room! Read on to learn what zinc whiskers are, where they come from, and what you can do about them.
WHAT ARE ZINC WHISKERS?
Zinc Whiskers are so small that the normal dust filters used on computer equipment are ineffective. If you want to stop zinc whiskers from entering your equipment you need HEPA filtration.
If you haven't heard about zinc whiskers before, you may be skeptical - It's easy to ignore a condition that is under the floor and barely visible at that. But the science behind zinc whiskers isn't a great mystery, nor is it really new. (Bell Labs reported on metal whiskering in the telecommunications industry back in the 1940s. Telecom companies are still dealing with whiskering from various metal sources today.) Ferrous metals such as steel are normally plated to prevent surface corrosion. Zinc is a very common plating material since it is fairly corrosion resistant, produces a good aesthetic appearance, and is reasonably inexpensive.
A normal bi-product of the plating process is high molecular level stresses in the plated metal. The crystalline structure within the metal will attempt to relieve the internal stress by enlarging the structure through the growth of crystals. The growth path is outward and the material is literally pushed out of the surface of the metal. These crystalline growths are known as whiskers. In the case of access flooring, the zinc electro-passivation coating on the steel sheet used to form the bottom pan of certain wood-core panels can have just the right makeup of zinc to promote whiskering of the zinc finish.
Because whiskering happens at the molecular level, the specific molecular make-up of the metal finish can literally prevent or exacerbate the problem. Moreover, the problem is not affected by environmental conditions such as temperature and humidity. If your panels are destined to grow whiskers, they will grow regardless of the environmental conditions.
"We had analog card problems on our old 3090 systems and then we lost 10 power supplies on our new CMOS processors." Fort James Corp.
Second, is the continually shrinking size of electronic assemblies. The lead pitch (lead to lead spacing) on integrated circuits and other components has shrunk dramatically. A whisker has a much better chance of causing a short on today's electronics versus 1980s vintage equipment. Even a small whisker has a chance of shorting two leads.
"We were changing to SP/2 equipment and started having a lot of errors", Manpower, Inc.
The same issue is true for tapes. The bit density continues to increase and therefore contamination can more easily obliterate a large portion of data.
On the human side, zinc whiskers are not known to cause any threat to people. Zinc is actually necessary in our bodies and is contained in most mineral supplements. Overexposure is not a factor since the concentrations in the room extremely small. And the whiskers themselves are not toxic like lead or asbestos.
WHAT SHOULD YOU DO?
If you don't know what kind of panels you have, follow
Note: Zinc whiskers only grow on panels that utilize electroplated steel. These panels have a uniform dull, or slightly shiny, gray appearance. Zinc plating can also be applied using Hot Dipped Galvanization (HDG). This process yields a bright mottled finish like on a metal wash tub. HDG plating does not grow whiskers. So even if you have wood-core panels, you are not at risk if they have HDG plating.
DO YOU HAVE ZINC WHISKERS?
Be Careful! This is the time to exercise caution! Zinc whiskers break off the panels easily. Sliding, or scuffing the panels will cause them to break off. Rubbing your hand over the panel will cause them to break off!
If you see whiskers, you now have proof. However, if you don't see whiskers, you can't automatically assume you are safe. You may not have checked the right panels, or the whiskers may not have grown enough to see.
An indirect but accurate testing method is wipe sampling of surfaces. If zinc whiskers are inside your equipment, they are also everywhere else in your computer room. With wipe sampling, a wet wipe is used to wipe a small defined area in the room The wipe is sealed in a plastic bag and sent to an environmental lab. The lab will then test for the presence of zinc on the wipe. The laboratory analysis typically costs less than $20 per sample with a 3-5 day turnaround. The lab won't be able to see individual zinc whiskers but they will be able to give you the concentration of zinc in the sample. If your wipe tests turn out positive, you've got whiskers!
More sophisticated microscope testing can be conducted to identify actual whiskers on specific components, such as a failure power supply. Although more expensive than wipe tests, Scanning Electron Microscopy (SEM) is essential in conducting failure analysis.
GETTING RID OF WHISKERS
In the long term, you don't have any option other than to replace the affected floor panels. The panels can be cleaned but the whiskers will grow back! You could seal or paint the bottoms of the panels but research has shown whiskers will grow right through most coatings. Moreover, the cost of painting would most likely exceed the cost of replacement panels.
Replacement is no simple task either. The more zinc related equipment problems you've had, the more careful you need to be. You first need to determine the extent of your problem. Inspect a number of panels (at least 20) to decide of you need to replace all your panels or just a few. The more you replace the bigger the potential impact of the project. Zinc Whisker remediation is a big deal and should only be undertaken after careful planning. Without proper equipment, personnel and procedures, the likelihood of success is low. The following outlines the general procedure for panel replacement.
Step 1. - Power down and REMOVE from the environment
any and all equipment that you can. If the whole room can be shut down,
Remember to map or mark panels that were not removed, if any. These panels should be monitored for continued whisker growth and replaced coincident with future equipment moves.
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