Abstract: An air flow supplied by a duct 10 adjacent a melt furnace 3 is normally directed downwardly through a plurality of nozzles 12 in the bottom of the duct towards a floor grate 13 or the like communicating with an exhaust duct 14, to thereby form a heat shielding air curtain 11 to protect the operator/controller. During the initial start-up period of the filament draw forming operation, however, a pivotal damper plate 15 adjacent the supply duct may be raised to deflect the air flow across the bottom of the orifice plate 4 of the melt furnace 3, to thereby cool the molten glass cones at the orifice exits and increase their viscosity, which serves to stabilize the filament forming conditions and prevent adjacent cones/filaments from converging together.