Upward flame spread over Nomex((R)) III fabric was tested in enriched oxygen, reduced pressure atmospheres. These are potential conditions for future space habitat environments. Flammability boundaries as a function of oxygen percentage and pressure were determined experimentally. Upward spread is possible at 24% O-2 for pressures as low as 7 psia. For most cases, upward spread is cyclic in nature. A cycle consists of flame growth, flame split, blowoff of the downstream '' secondary '' flame and re- growth of the upstream '' primary '' flame. This article presents a detailed description of this interesting and unexpected phenomenon, and suggests that a two- stage solid pyrolysis is its cause.