Firefighters don't use grinders. They use a combination of sawzalls and the jaws of life. I promise you that you do not know more than the guys who do this every day for a living. The sawzall with carbide blades is the correct tool among those readily available to the public. You can't finish your cut faster than a gasoline fire can kill both you and the person you were incompetently trying to save. The fact that you can't grasp the risk of lighting a fire with grinder sparks tells me your knowledge of grinders comes from reading the internet. As an emergency preparedness bonus the same sawzall can be used for clearing downed trees from the road just by swapping blades while a grinder cannot.