To sum up Hazmat Awareness in a simple post, we can forget using the DOT guide, and just go for the copometric system of hazard identification. In order to do this, simply park a safe distance from the scene, and view the cops through a pair of binoculars:
If the cop car is running, and the cop is lying on the ground, you are dealing with a toxic atmosphere.
If the cop car has stalled, and the cop is down, you are dealing with an oxygen depleted atmosphere.
If the cop and car are both on fire, you are dealing with a flammable atmosphere.
If both the cop car and the cop are melting, you have corrosives to deal with.
Hope this helps.