Content that flashes or flickers can trigger seizures in susceptible individuals. Therefore flashing or flickering content should be avoided.
The best technique for addressing this issue is to avoid using content that flashes or flickers. Not only can it cause seizures, but it's likely to be annoying or distracting for users in general. If you must use content that flashes or flickers, test your content using methods describe below to be sure your content flashes or flickers at a safe level.
The W3C Web Content Accessibility Guidelines 2.0 includes specific technical requirements for determining whether content flashes or flickers at an unsafe level. In general, if content flashes more than three times per second, it is unsafe. However, the W3C provides a more precise technical formula for calculating general flash and red flash thresholds. The Trace Center at the University of Maryland has developed a Photosensitive Epilepsy Analysis Tool (PEAT) for measuring whether web or computer applications are likely to cause seizures.
External WCAG Reference
Most Details from this page were gleaned from the University of Washington's Accessible Technology section.