There are no national guidelines for administrators on determining threat levels

A Time's article has this:

Faced with increased threats, the challenge for schools is to determine when to evacuate. There are no national guidelines for administrators on determining threat levels, and most decisions to close are made by superintendents and school boards, often in conjunction with police departments or emergency services. 

My question is about this sentence:
There are no national guidelines for administrators on determining threat levels

In this sentence, there are two prepositional phrases "for administrators" and "on determining threat levels".

Do these phrases modify "guidelines" or "are" or the entire sentence?