The term "volunteer" refers to a group of part-time or on-call firefighters who have other occupations when not engaged in occasional firefighting or response to other emergencies. Although they may have "volunteered" to become members, and to respond to the call for help, they are compensated as employees during the time they are responding to or attending an emergency scene, and possibly even for training drills. An on-call firefighter would probably be expected to volunteer time for other non-emergency duties as well (training, fundraising, equipment maintenance, etc).
So we'll be there this evening to support our local "volunteer" firefighters. They serve very good catfish (photo).