 firefighter' means any officer or employee of a fire department of a contracting agency, except one whose principal duties are those of a telephone operator, clerk, stenographer, machinist, mechanic, or otherwise and whose functions do not clearly fall within the scope of active firefighting, or active firefighting and fire prevention service, active firefighting and fire training, active firefighting and hazardous materials, active firefighting and fire or arson investigation, or active firefighting and emergency medical services, 