Roach, S. A.
1981 The Annals of Occupational Hygiene, Vol. 24, No. 1, pp. 105-132, 1981
Roach, S. A., (1981), "On the role of turbulent diffusion in ventilation", The Annals of Occupational Hygiene, Vol. 24, No. 1, pp. 105-132, 1981.
Abstract:
he effectiveness of exhaust ventilation for reducing concentrations in the vicinity of employees is influenced by turbulent diffusion as well as by the bulk air movement induced. Simple models are analysed to show how these two factors combine and how the conclusions fit in with established rules-of-thumb. Tests of fume cupboards conducted in a strictly practical setting confirm that it is inadvisable to design the ventilation of an exhaust hood so as merely to produce a standard capture velocity or standard entrance velocity, as the velocity chosen may be excessively high or, what would be worse, not high enough. A more reliable procedure is to measure the performance quantitatively of the same or a similar hood with respect to the concentrations in the breathing zone of employees in a similar environment with similar general ventilation provisions and design with these results in mind.
Changes in release rate of contaminant cause proportional changes in concentration, whatever the ventilation pattern. The effect of differences in features concerning hood or room configuration and ventilation distribution or quantity are best estimated by measuring the consequences of such changes on the effectiveness of an existing installation. The theory outlined in this paper may help in making predictions from limited information of this nature.
