South-East Essex College

Client - Fulcrum Consulting

Fume cupboards are to be installed in the new South-East Essex College building in Southend-on-Sea. The fumes are to be extracted via exhaust stacks on the roof of the building, which, according to building regulations should be constructed so that the tops are either 3m above the highest point of the roof, or at a height of 1.25 times the height of the building; whichever is the highest. Since the highest point of the building will be about 35m above ground level, adherence to the regulations would require the top of the stacks to be about 44m above ground level.

The design of the building consists of five stepped ‘tiers’ with step heights of about 3.7m. It is planned to locate the exhaust stacks on the top of the lowest tier, which is at a height of about 16m above ground level. It is hoped that the height of the stacks may be safely reduced below the regulation height stated above, without there being an undue risk of contamination.

Flow Analysis have conducted a CFD investigation of the air flows in the vicinity of the new college building and the consequential fume dispersal characteristics. The purpose of the study is to aid the design and placement of the exhaust stacks and to provide evidence to verify that the chosen design presents a low risk of contamination either through the plant-room intakes or to the surroundings.

By far the most significant risk is posed by the westerly wind, for which 0.22 % of the stack exit exhaust is predicted to enter the 7^th floor rooftop plantroom enclosure. The importance of this inflow may be determined from an analysis of the composition of the exhaust, and knowledge of the concentration levels of any contaminants which should not be exceeded for health reasons.

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