Atkinson Science used VU.CITY's 3D model of the surrounding campus to test the rooftop flues on one of the University of Birmingham's main research buildings.
The Institute of Biomedical Research (IBR) is a six-storey building on the University of Birmingham's Edgbaston Campus. It carries out 20 to 30% of the university's research. Its flat roof has two rows of flues carrying air from fume cupboards and safety cabinets, with a band of cladding running round them to hide them from view.
At the time of the study, the flues had to be shut down whenever maintenance staff needed to go up on the roof. Each shutdown interrupts research. So the university's Estates Office asked Atkinson Science to find out whether the flues were tall enough for the rule to be lifted.
In normal use, the air leaving the flues carries pollutants below the long-term exposure limit. The risk comes from a spill in a fume cupboard, which can raise the concentration tenfold or even a hundredfold. There is no regulation on how much a flue discharge must be diluted before it reaches people. Atkinson Science works to at least 100 dilutions, which covers that kind of accident.
Flat roofs also bring a known problem. Wind separating off the edges of a building creates recirculating air over the roof, and fumes released too low can get caught in it.
Atkinson Science built a CFD model of the IBR and every building within 300 m of it. VU.CITY supplied the geometry of the surrounding buildings, and the terrain was simplified separately. They ran the model at wind speeds of 0.25, 2.5 and 10 m/s, from the north and every 45° round from there. For each flue they plotted the zone where fumes had been diluted fewer than 100 times.
At 10 m/s from the east, the wind hits the cladding almost head on. The flues and cladding act as one large obstruction, and air dropping down on the far side pulled fumes from the west row onto the roof. With the wind from the north, some fumes were caught at the downwind end of the cladding. As built, the roof is not safe to work on while the flues are running.
Atkinson Science then tested two changes in the model. Without the cladding, the fumes cleared the roof in the easterly wind. In a northerly, fumes still gathered behind each flue, because air was leaving the flues at only 3.4 to 10 m/s. Narrowing the flues so that every outlet ran at 20 m/s stopped that.
The restriction on roof access stays in place for now. The study gives the university a clear set of design changes to consider if it wants to lift it.
Read the full case study, with all of Atkinson Science's CFD images, on their website.
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