Third Level Escalation

[Siora]

How do I create a third level escalation within the same SLA plan? What I mean is this:
1. Ticket is created and goes overdue
2. Ticket gets escalated to second level and goes overdue
3. Ticket gets escalated to third level

I don't see how the third level can be implemented because the way I see it the two escalation rules would conflict with eachother because there is no way to determine when to escalate to which level of support.