All positions in bureaus of fire, except as here and after provided, and all positions of fire alarm operators and fire alarm box inspectors in bureaus of electricity, in cities of second class, shall be in the competitive class of the civil service of such cities. This act shall not apply to or include chief officers of bureaus of fire under the director of the department, by whatever title his position may be designated, nor to chief clerks in bureaus of fire in such cities.
53 P.S. § 23491