If your helmet split it means it failed. That's not how they work.
That isn't what the link you posted says. The last line is:
'disregard the breakages and look to see if what's left of the styrofoam has compressed. If it hasn't, you can be reasonably sure that it hasn't saved anyone's life.'
If your helmet split it means it failed. That's not how they work. What make of helmets were they?