As a general rule of thumb IMO, ( I'm studying scene size up and the assessments module right now) if you come into an area of an MVC, you should look and smell for fuel leakage- as throwing flares down would not be the greatest of ideas in that scenario, plus you also have the possibility of downed power lines that could ignite fuel as well. I'd say if you were off duty or whatever the best bet would be find something reflective if you have it or just use a flashlight to direct traffic around the incident. even if you are uphill from it. You would be covered under Good Samaritan Laws; just make sure you stay there until someone shows up, otherwise you can still be liable for abandonment. Watch out for maintaining the c-spine too; you might do more damage to the patient than you are helping them without a KED extrication . If there are LEOs on the scene already; that is just an ethical judgement by you to stop or not; 9-10 times they are gonna tell you to move along anyways.
and also- just because the vehicle is not on fire when you arrive does not mean it wont catch fire later- constant scene size up. There wouldn't really be any documentation involved on your behalf other than stating your observations and procedures you did to the ones in charge of the scene.
veterans- am i right on this?