Statement of the Project

University campuses have large numbers of fume hoods that are designed to dilute and disperse potentially harmful chemicals. In a campus where the buildings are in close proximity there is a possibility that the exhausts from the ume hoods from one building can be drawn into the air intake ducts of another. The problem is difficult to analyze because of the complex air flow patterns over buildings. Depending on the meteorological conditions downdrafts can occur which bring the exhaust from the stacks down to ground level, a problem that can be aggravated on a hot summer day when the plume from the exhaust from an air conditioned building can be denser than the ambient air. Estimations of the plume trajectories and exhaust dilution are made difficult by the complex flow patterns around and between buildings (You must have experienced the acceleration of the flow under the Green Building and the swirling motions on the North side of the passage connecting Buildings 56 and 66). It is because of such complexities that tracers are used to determine the fate of contaminants.

One tracer that is commonly used is sulfur hexafluoride. It has the advantages of being gaseous, chemically inert, non-toxic, insoluble in water and detectable at very low concentration. A gas chromatograph with an electron capture detector can pick up one part of sulfur hexafluoride in 1012 parts of air. It has been used in tracer studies (P. Drivas, Ph.D. Thesis, California Institute of Technology, 1975)to study the ventilation systems in buildings, airflow within the wake downwind of a building, dispersion of from an urban highway, and large- scale transport and dispersion over the Los Angeles area. As a measure of the sensitivity of the technique SF6 released in Anaheim was monitored over 100 kilometers away in Palm Springs. One of the interesting results by Drivas was that in one experiment at Caltech 20 percent of the fumes exhausted by a roof fume hood were found to reenter the ventilation system through the main ventilation intake located only 16 feet away!

The project is to

1. Assess the potential problems that may be produced by the exhaust from fume hoods using correlations for plume dispersion available in the literature and use these to assess problems that may occur on the MIT campus from the dispersal from fume hoods.

2. Set up a system for experimentally measuring the dispersal from fume hoods. Develop confidence in the use of the method by evaluating the ventilation in Building 66.

3. Apply the methods to test the models for fume hood dispersal. The systems to be studies should be arrived by consultation the MIT Environmental Medicine Service, taking into account the results from part 1 and 2 in the design of the experiments. The validation of the methods for assessing fume hood design is particularly timely as MIT begins to refurbish the fume hoods in Blgs. 16 and 56, part of which will be occupied by the Department.