CD shattering

CD shattering, a phenomenon also known as exploding CDs, occurs when a CD shatters inside a high speed CD-ROM drive (48X or higher) with a loud cracking sound. Typically, the disc and the drive will be ruined. Fragments of the broken disc may be expelled through the front of the drive at high speed and cause physical injury.

Maxell's senior marketing manager, Dawn Wortman has been quoted as saying there is very little danger at 48x, and danger of shattering only becomes significant at above 48x (or 52x).

"The 48X standard offers customers outstanding performance without the risks associated with 52X speeds," says Dawn Wortman.

A disc shatters when it fails to support the centripetal force required to keep all parts of the disc moving circularly. The velocity of the edge of a 120 mm disc rotating at 10,350 RPM is approximately 65 m/s. (234,1 km/h, 145.5 mph) To remain in circular motion about the spindle, the disc edge accelerates at about 7,200 G. The force causing this acceleration is transmitted through the disc itself and is balanced by an opposite force on the other side of the disc. Thus, a disc begins to fail when it can not handle these forces, and a failing disc can then completely shatter due to the imbalance of forces around the disc.

The television series "MythBusters" conducted experiments in which they succeeded in shattering otherwise undamaged control CDs at speeds in excess of 23,000 RPM. A 52x drive using CLV needs to go up to 27,500 RPM when reading the inner track, however very few drives reach those speeds, reading data at a slower rate on inner tracks and only achieving 52x read speeds on the outer track. (In other words 52x is the peak read speed, not the typical rate.)

Typically a 52x drive will actually max at around 11,500 RPM. At this speed it is still possible for a CD to shatter with enough force to come flying out of a drive. This happens when brittle media is put in the drive. small cracks can occur on the inner hole of the disc. Once these cracks reach a critical length, they propagate in an instant and the disc shatters. The critical length of the crack is a function of the rotational speed. If the drive is spinning below 8,000 rpm or around 40x the critical length of the crack is long enough that the crack enters the disc media before becoming critical. At this point the crack enters the media, the drive detects the error and slows down.

Many drive manufacturers now have more aggressive back-off algorithms that detect issues with the disc and this reduces the chance of the disc shattering. Some companies also deliberately slow their drive down to 40x and the user has to press a combination of buttons to allow 52x speed to be reached. In doing so, the user takes the responsibility for any issues arising from disc shattering.

External links

* [http://www.qedata.se/e_js_n-cdrom.htm The Case of the Exploding CD-ROM Record]
* [http://www.dvd-recordable.org/Article246-mode=thread-order0-threshold0.phtml Life in the Fast Lane Can be a Disc-Shattering Experience]
* [http://www.powerlabs.org/cdexplode.htm PowerLabs High Speed CD-Rom Experiments]
* [http://www.afterdawn.com/news/archive/3574.cfm Maxell Introduces 48x Media]
* [http://www.choice.com.au/viewArticleAsOnePage.aspx?id=103535 Guide to Safer High Speed CD Use]
* [http://www.rm.com/safety A UK site giving more information about CD Rom shattering]
* [http://www.rm.com/safety/Downloads/StructuralIntegrity.pdf Paper on the Structural Integrity of CD Rom Discs]