Abstract: A door assembly is provided for use in proximity to door openings wherein there is a large amount of material handling vehicle traffic. The assembly includes a frame mounted within the door opening and having upright elongate side sections. Each section has an interior guideway with an elongate entry thereto. Within each section is a pair of guide members forming therebetween a gap aligned with the entry. A flexible door member is slidably mounted on the frame. Opposite marginal side segments of the door member extend through the entries and gaps into the section guideways. Each marginal segment is provided with a plurality of relatively spaced, vertically aligned follower elements normally impassable with respect to the gap.