Road Crash Rescue revision: Chapter Six "Managing a Road Rescue Incident Scene"

Hi everyone,
[Explanation from the first post in this series] I’ve been posting questions on Facebook Notes to help both me and my friends prepare for our “Road Crash Rescue Operator” assessment.  It struck me that a lot of the questions would have essentially universal answers, and that it could be interesting to compare notes where the answers aren’t universal.  So, I’ll run a series of posts setting out the questions that I’ve prepared – after they’ve been up for a while I’ll put the questions in the comments.
The questions are all drawn from the Country Fire Authority / State Emergency Service’s Road Rescue Learning Manual (2nd Ed., Melbourne, 2008).
And now, today’s questions:

What is the rule of thumb for locating warning devices relative to the scene of an accident?
What are appropriate fire extinguisher types for vehicle fires?
Where an LPG fuel spill occurs, how will the fuel behave?
What particular concerns may be presented by a collision with a fixed object?
What are recommended steps for dealing with a non-deployed airbag?