I know of someone who coasts his bike to a slowspeed stop, as his disability comes into effect.
Just before the full stop, the fall-down, on the side --- happens.
(since the helmet purchase) Sometimes -- the first crack shows up, on the first fall, of above. But most of the time, it takes a few multiple falls that the helmet be unsafe to use anymore. It varies on the falls, of the width of the cracks. But normally on the pressure/what the fall be on; speed of the fall.

Helmet foam design really never gets improved over time. Just the shell.