Abstract: A fume hood is fabricated of three or four like modules to a desired partial or full cylindrical structure having a reaction chamber therein. Each module has an upstanding, arcuate circumferential outer wall and an upper wall and base extending inwardly therefrom in coincidence above and below one another. The top wall and base have the shape of a sector of a circle with their apexes opposite the outer wall and the outer wall being the arc of the sector. An inner wall spaced interior of the outer wall defines an exhaust passageway therebetween with movement of gases and air being through exhaust ports through the inner wall. The exhaust ports are spaced apart between the top wall and base and are at constant certain distances from the top wall and base.