CofC Web Accessibility Guidelines- Rule (J)

(j) Pages shall be designed to avoid causing the screen to flicker with a frequency greater than 2 Hz and lower than 55 Hz.

Translation: If you have some kind of animation, it shouldn't flash between twice and fifty-five times a second.

What to do: You could certainly argue that flashing graphics constitute poor design to begin with. The best solution is to avoid flashing graphics altogether.