The people that work in an ambulance are called Paramedics. They are healthcare professionals that work in emergency medical conditions. Paramedics can also work in emergency response vehicles and mobile units that are known as cycle response. Visit http://en.wikipedia.org/wiki/Paramedic for more information.
They are either paramedics, emts, and firefighters. Most states in the us in order to work for the city or county fire department you must be at least a nationally certified EMT and nationally certified firefighter.