One who gets unusually fervent about a hobby or vocation; to the point that it dominates conversation, free time and daily life.
Who's that driving around in that pickup truck is that with all the red lights and chrome sirens? It has a sticker of Calvin peein' on a fire in the back window and a "My other car is a fire truck" license plate frame.
Oh, that's Freds. His is a stemwacker volunteer fireman.
A firefighter who has several hundred dollars in emergency warning equipment on his/her personal vehicle. Usually accompaned by several radio antennas. The typical woo woo may be wearing a fire department shirt in a public place and also sport a walkie talkie, fire department pager (or two) a cell phone (or two) on their belt.