The line of duty entitling one to participate in the fund shall be so construed as to mean actual fire duty only, and any actual duty connected with the fire department or county fire marshal office when directed to perform the same by an officer in charge. (1891, c. 468, s. 5; Rev., s. 4395; C.S., s. 6060; 1925, c. 41; 2004-199, s. 22(b).)