People with photosensitive epilepsy can have seizures triggered by flickering or flashing in the 4 to 59 flashes per second (Hertz) range with a peak sensitivity at 20 flashes per second as well as quick changes from dark to light (like strobe lights). 

If using the <blink> tag, does the "blinking" or flickering really add to the content or functionality of the page? If not, leave it off - if you do need to include screen flicker, ensure that it is slower than 2 flashes per second or faster than 55 flashes per second.