Ryl isn't letting me quote but to me actively engaging in suicidal behaviour would be having taken an overdose or something along those lines.
I guess for me the threshold would be if I had the persons address I would call the police to do a welfare check or call for an ambulance etc. I think I've done to RYL friends on 3 occasions.
So someone who has self harmed, binged, purged, fasted, etc wouldn't count nor would someone who was posting whilst psychotic, manic or dissociated. Unless their life was in immediate danger.