Several people have emailed me as of late, not understanding how the rank structure works in the fire/EMS field. As a general guide, I will try to spell it out. Since fire departments nationwide differ in titles and terminology, I will say that what is true for most departments is not always true in others.
As a general rule, the fire and EMS service follows a quasi-military rank structure, with each person in the department knowing the chain of command, and their place in it.
Ambulances (no matter what they are called) typically have two people assigned, many times an EMT (who is the driver) and a paramedic. The paramedic is in charge.
Engine and Ladder trucks typically have a Company Officer and Driver, along with one or more firefighters. (The driver is not a rank everywhere) The officer is in charge of the unit, and the engineer is basically his platoon sergeant.
An ambulance and an engine or ladder are frequently bundled together. In such a case, the officer on the engine outranks the paramedic. In some cases, the driver of the engine does as well.
Other positions include district supervisors called battalion Chiefs, who supervise 5 to 8 engine/ladder crews, and Division Chiefs, who supervise 5-8 battalions. The idea is to keep the number of supervised personnel to a manageable level, and 5-8 is it. This is called the ‘span of control.’
Orders given are to be obeyed. The senior officer calls the shots. This must be so, because when snap decisions need to be made on an emergency scene, ruling by committee doesn’t work.