As used in this article the term “firefighter” shall be deemed to include only a member of a fire department of cities, counties, cities and counties, districts or other public or municipal corporations or political subdivisions, whether the members are volunteer, partly paid, or fully paid, excepting those whose principal duties are clerical, such as stenographers, telephone operators and other workers not engaged in fire-suppression or rescue operations or the protection or preservation of life or property. These firefighters shall be regularly employed, or in the case of a volunteer, shall be regularly enrolled as such.