Combustion air ducts or
plenums shall not be installed so as to require openings in or
penetrations through construction where fire dampers are
required. Manually operated dampers shall not be installed in
combustion-air openings. With prior approval, power-actuated
movable louvers admitting combustion air shall be
permitted to be used and, where installed, shall be electrically
interlocked with the main burner fuel-supply valve so as to
prevent fuel delivery unless the louvers are in the fully open
position.