Medium-sized engines can be used either for wildland fire operations or structure protection in the wildland-urban interface. A crew of three to four is required to operate these engines.
Engine crews are used for initial attack on developing fires close to roads. The crew can hike or be flown to fires in more remote areas. During extended attack, engine crews support fireline production, structure protection, and helicopter operations. One advantage of engine crews, as compared to hand crews, is the ability to build "wet line". Wet line is fireline that uses water or foam in place of digging a fireline to mineral soil. This minimizes the impact to vegetation and limits erosion.
Information from www.nps.gov/fire