The selection of fabric materials used in fire safety critical applications, such as firefighters, car racers and astronauts suits, is an important task based on minimizing the risk that they can represent. Fire resistant materials are clearly preferred however their flammability properties can change depending of the ambient conditions at which they are exposed. Therefore a material that is expected to be fire resistant can present a different behavior under different conditions. In this work, experiments were conducted to study the influence of environmental variables such as oxygen concentration, ambient prebure and external radiant heat flux on opposed flow flame spread over a thin fabric sample in a mixed buoyant/forced flow. Flame spread rates and Flame/No-Flame propagation boundaries were measured for a Nomex-based fabric sample over a range of conditions. In the experiments ambient prebures going from 40 to 100 kPa with oxygen concentrations varying from 25% to 33% were considered. An external radiant heat flux supplied by infrared heaters was used to study the influence of this additional variable. The experimental data showed that close to the limiting conditions for flame spread, as ambient prebure is reduced an increase in oxygen concentration or the external heat flux is required for the flame to propagate. At higher values of oxygen concentration, flame spread rate measurements confirmed a positive dependence of oxygen concentration, ambient prebure and external heat flux. The results of this work provide a better understanding of how different environmental variables influence the flammability characteristics and the burning behavior of fabrics in conditions different to those used in standard flammability tests.