The air-vestNew devices eliminates the eddy that develops in front of a worker standing in the open face of a fume hood. Normally this eddy draws some of the pollutant, commonly generated near and in front of the worker, towards the worker's breathing zone. Experiments at LBNL have demonstrated that worker exposure to pollutants in the breathing zone can be reduced by about a factor of 50 while direct energy consumption of the fume hood is also reduced. Large savings in indirect energy (used in the building to condition make-up air) are also estimated to result from the use of an airvest along with a reduced fume hood face velocity. Annual savings are estimated to be about $1,000 per hood, per shift in Chicago weather; actual savings would vary according to local climate and number of shifts. [Gadgil et al., 1992]
The following was excerpted from a research paper produced at the Lawrence Berkeley National Laboratory (LBNL), Energy and Environment Division, University of California, and presented at the 1992 Indoor Air Quality Conference:
Substantial reduction in the fume hood airflow without compromising the performance of the exhaust hood can be envisaged if a device can be designed that makes the worker essentially transparent to the flow of air into the exhaust hood. The worker could wear the proposed device, called an "air-vest." It would draw air from the back of the worker, and expel it in the front. Under ideally matched flow conditions, the resulting airflow pattern behind and in front of the worker would be identical to that obtained without a worker blocking the flow. No back eddy would develop, and pollutant removal and transport would be as effective as that with an unobstructed exhaust hood. Under conditions of imperfect matching, the hood performance may be improved because the air-vest ventilates the region of the eddy.
Reduction in the breathing zone concentration of an experimentally simulated pollutant, by factors ranging from 100 to 800, was observed with the device (called an air vest). With use of the air-vest by the worker, the hood face velocity can be reduced, leading to substantial energy savings in conditioning of make up air in the building.
Experiments using a heated full-size mannequin were conducted with a full-scale walk-in fume hood. Sulfur hexafluoride was used to simulate pollutant generation and exposure during a work situation. Flow visualization with smoke was also undertaken to evaluate the air-vest qualitatively.
The air-vests tested in this project were very rough prototypes. However, they have demonstrated the proof of the concept, as intended in the project objective. Reduction by factors ranging from 100 to 800 in the breathing zone concentration of a simulated pollutant was observed with the use of an air-vest on a heated mannequin in a full sized fume hood. Air-vests could therefore be useful in meeting the declining limits on acceptable worker exposure to various industrial pollutants.
Reduction in the bulkiness and power consumption of the air-vest designs described here appears possible with additional work. Further investigation should address issues such as the shape of the front manifold (to make it less bulky), the position of air-intakes, the method of supplying air to the air-vest, and air-vest performance in field settings with real workers. For this purpose, collaboration with industry would be desirable. The future research effort should also address the possibility of failure modes of the air-vest (e.g. pollutant exposure at different orientations of the air-vest to the hood air flow, and for different release points and release velocities of the pollutants than those investigated here). [Gadgil, 1992]