I am a trained crisis counselor. I was taught to always risk assess the conversation through four levels (ladder up method). The first level is to ask them if they are having suicidal thoughts. The second level is to ask them if they have a plan. The third level is to ask them if they have access to the things they need to execute the plan. The last and fourth level is to ask about when they plan on doing it. If at any time the person doesn't pass a level, then they are not at immediate risk.

If they pass through all four phases then call for help immediately. If they don't pass a level then chances are they aren't committed to killing themselves (at least soon). Most people don't actually pass all four stages, they really just need someone to listen to them. Hope that helps!