An infant container which may be in the form of a crib mattress and crib bumper assembly having means defining one or more gas flow channels which permit any concentration of heavy gases to drain by gravity from the upper surface of the crib mattress and be replaced by the environmental air of the room in which the crib is located. The gas flow channels may be defined by the crib mattress, the crib bumper or the structure of the infant container or may be defined by a structural element that elevates a conventional crib bumper above the upper surface of a conventional crib mattress and which defines at least one and preferably a multiplicity of gas drain channels. The heavy gases may be dissipated from the infant container by gravity induced gas flow. The system for removing heavy gas concentrations from the region of the upper surface of crib mattresses may also take the form of a mechanized system being suction operated or having air blowing capability for forcibly removing heavy gases from the upper surface region of the crib mattress so that the heavy gases are replaced by the environmental air of the room in which the infant container or crib is located.