Why Degauss Your Media?

Authored by Don Blackburn - BOW Industries, Inc.

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In spite of all the material written about degaussing, most of it is in a format not easily understood by an average person. I wanted to try to answer some of the questions that cause about 90% of the confusion. First however we need a simple glossary of common terms and a couple "Rules of Thumb". 



Origin: Karl Friedrich Gauss, 1777-1855, was a German mathematician, astronomer and physicist.

Definition: Gauss is a unit of measurement of magnetic flux density produced by a magnetic force (coils).

Translation: Gauss is the amount of energy that is produced by a magnetic force (coils). Gauss is a measurement of coil strength.


Origin: Hans Christian Oersted, 1777-1851, was a Danish physicist.

Definition: A unit of magnetic intensity equal to the intensity of a magnetic field in a vacuum.

Translation: Oersted is a measurement of magnetic intensity applied to magnetic media. 


Definition: The amount of applied magnetic field (of opposite polarity) required to reduce magnetic induction to zero.

Translation: The ease (or difficulty) by which magnetic media can be demagnetized. 

NOTE: The words oersted and coercivity are often used interchangeably, which only adds to the confusion. Newer technology tapes generally have a higher oersted rating than older tapes.


Rule of Thumb #1

The higher the oersted rating, the more energy needed to degauss it.

Rule of Thumb #2

In order to degauss magnetic media, a magnetic force (gauss) of 2 to 3 times greater than the oersted rating of the media should be created.

Therefore, in theory magnetic media with an oersted of 1800 would require a magnetic field strength in the neighborhood of 3600-6400 gauss in order to properly degauss it. 


Why would anyone want to degauss magnetic media in the first place? Media is degaussed because there is either laws or regulations on the books that requires that media be degaussed or you simply want to reuse the media.

For starters, we degauss media for:

1. Declassification for security purposes or to conform to privacy laws.

2. Reuse of media. Degaussing eliminates recording errors from residual magnetic signals.

3. Disposal purposes.

There are dozens of Federal and State laws relating to data privacy - Fair Credit Reporting Act, Freedom of Information Act, Title 28, Buckley Amendment (Educational Records), and many more. 

Today's records relative to insurance, consumer credit, bank records, etc., all must meet various standards of data privacy. Also, lets never forget national defense. 

In short, if magnetic records get tossed out without being degaussed and someone recovers the data - you've got a BIG problem. You could be looking at a very expensive lawsuit or even jail time. 

Degaussing simply makes sense. But, you say, "I don't know anything about degaussing." Don't be alarmed - you've got a lot of company!

A long time ago, someone developed this thing called a degausser. The early versions were crude by today's standards and looked something like a hot plate. Confidentiality in those days wasn't as critical as it is today. Times have changed and we are concerned that sensitive information might fall into the wrong hands.

Let's suppose that you have a cartridge or reel of magnetic tape that is already encoded and you want to dispose of it. OK, we'll degauss it.

So, how's it done?

Basically, all you do is introduce the recorded magnetic media into a very strong magnetic field and uniformly withdraw it from this same magnetic field. As it is leaving the magnetic field, the magnetization of the recorded data becomes weaker and weaker until there is no residual magnetic signals remaining on the media. In other words, you put it in (magnetize it) and you take it out (demagnetize it).

However, some media is harder to degauss than others. For example, a standard VHS cartridge tape at 650 oersteds is easier to degauss than a cartridge at 1800 oersteds. In fact, most cartridges being used today have a high coecivity rating - most around 1800 oersteds.

All this means is that you should choose a degausser depending on the coecivity rating of the media to be degaussed. A degausser designed to degauss media with a maximum coercivity rating of 650 (VHS) oersteds will not properly degauss media at the 1800 oersted rating.

Coercivity is a measure, in oersteds, of the magnetizability or erasability of a tape, cartridge or hard drive.

The higher the coercivity number the more energy needed to degauss it. The higher the coercivity the harder it is to erase.

So, all you really have to know is the bit about withdrawing the media from a strong magnetic field in order to degauss it. Given the type of media and the quantity, you will be able to choose the proper degausser.

When choosing a degausser, cost should not be the deciding factor. Consider the sensitivity of the data to be degaussed; the frequency of degaussing; the laws relative to the destruction of records and then choose the proper degausser for the job to be done. Please call our sales staff at BOW Industries for any assistance you may require.

IMPORTANT: Some media, such as 3590 and LTO cartridge tapes and hard drives should not be degaussed unless being done for destructive purposes. Degaussing will destroy the servo tracks or chips rendering the media useless.

One should also consider physical destruction in addition to or in place of degaussing depending on the requirements and budget. Please see BOW's line of destroyers.   

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Last modified: August 13, 2014