A conventional form of scraper-chain conveyor with a series of channel sections each having a floor disposed between sigma-shaped side walls has upstanding spill plates, C-shaped covers and hollow spacer bars attached to the goaf side of each channel section. These components define upper and lower guide channels for a drive chain circulated along the goaf side of the conveyor which is connected through a sword plate to a machine guided for movement along the conveyor. To prevent gases from building up beneath the conveyor vents are provided in the goaf side wall of the channel sections and these vents communicate with the external V-shaped grooves in the side walls.Vents are also provided in the spill plates to establish communication between the V-shaped grooves and the upper chain guide channel. The covers are then spaced apart to form apertures allowing any gas which reaches the upper channel to pass to the surroundings. To prevent fine material from blocking the gas vents, guard plates are provided on the spacer bars in the upper channel which form barriers which surround and shield the vents while permitting gas to pass into the upper channel.