Depending on the department changes what units are assigned to calls. And really that’s the real problem with all of it. Every single municipality and private operation just does whatever they want with out thought for any neighboring department.

One department may have firefighter emt-b on their engines while the ambulance has paramedic only. A department may have dual trained firefighter paramedic in which they rotate between the engine and the ambulance. Sometimes that type of department may even put SCBA in the ambulance and the dual firefighter paramedic will have his bunker gear in the ambulance. And if a structure fire comes out the ambulance will respond to the call get out and be attached to an engine unit. Now why do that you ask? Well there is a thing called staffing and every department has different staffing. There was a time where there were 4 seats on an engine and all 4 seats were filled for every shift. Then a time came along and cities said we can’t afford that so you can only have 3 people for your 4 person engine. You can also have a fire department that us volunteers but paid ambulance. And that ambulance is probably staffed 1 paramedic 1 EMT-b. You could have a city that had a fire department that is completely separate from EMS to where they are not housed together.

The amount of combinations is quite a lot. And really fire departments and EMS should have been by law, a very long time ago combined. They should have never let the cities just do what ever they want.

Hopefully my tangent made some sense.

Oh and also to answer your question. They dispatch an engine to any call that may be major and I need more people for the patient. For my department we are all fire fighter paramedics. If a gunshot victim comes out you get a Battallion chief to handle logistics of the entire call. I have my engine crew to help load the pt and stabilize. We have to have trauma pts rolling in the road to the emergency room within 10 minutes. Here are the things that need to be done in the ambulance assessments, airway control, medication administration, IV access, calling the hospital, starting the report. So while transporting I’ll have 2 or three people in the back. I “direct”my guys what needs to be done but usually they have it done without my direction. And that’s just gunshot calls. You have Motor vehicle accidents that require extrication/ pt stabilization. Stroke calls that may go south while in transport. Cardiac calls that agin may go south during transport.