Why do they have Fire Engines respond to physical injury/death?

Reason one, manpower. Accidents can result in multiple or serious injuries requiring that manpower. Two, safety. The engine often serves as a roadblock, to force people to slow down and go around the work area while patients are being taken care of. Third, precautionary. Even if there is no fire, there may be oil or other fluid leaks. The engine carries material to soak up the liquids and keep it from getting into the drainage system or water supply. They also are able to provide extrication assistance if a person is entrapped in an accident.

While it is more expensive to send an engine all the time, it is also better for the patients. If the engine is not dispatched until after the medics arrive on scene, the quality of patient care may suffer. In some cases, it may mean the difference between life or death. So, most agencies prefer to spend the extra fuel to put the engines on the call from the start.

They usually work hand in hand, when there is a bad accident and EMS comes out they will as well since they made need to block off the street. A fire can also break out and its also their job to use tools to cut a car in half to get a victim out. EMT's dont really have those tools

So look at Fire Engines as the 'muscle/man power' for EMS. EMS provides care, Fire Engines make sure they can do it quickly and effectively

Its the cops job to serve and protect, doesnt make them firefighters though

Firemen are also trained as first responders. Some are even paramedics.

It is common to send them to accidents because fluids leak and fires may start.

Firefighters in my area are also very helpful in directing traffic and cleaning up the mess from accidents.

Having firefighters to perform these other tasks allow the police to concentrate on the safety of the scene and allows paramedics to concentrate on the injured.

To physically assist the paramedics on the ambulance.

Also, at least in my city, at least 1 member of every engine company is an EMT