That is one very well made video, I was thoroughly convinced that it was the real deal until reading all the posts.
My initial reaction to rolling up to the scene like this (with what info was given to the LEO) I would obviously stop and backup immediately, notify county that there is an obvious leak coming from the tank with one person down not moving, Since it looks like the cruiser is situated downwind, I'd be backing up quite a ways, once I felt I was safe I'd stop and gear up with whatever protective clothing my rig would have, get the eyes out and try to give the incoming fire units as much info (pt movement, placard info/tank description, app wind speed and how much gas in escaping) based on what I could see. I'd also contact my local hospital to give them a heads up on potential pts. Once fire is on scene and get the scene under control, then I'd have them check the potential pts to see if they are viable or not. If not then I'd contact the hospital again and tell them to stand down due to the pts being doa. Contact fire command to set up EMS support for the fire crew and set up for deconing of the rig and crew if needed.
Never experienced a true HAZMAT incident such as this and I'm sure my skills are a bit rusty.