Semester

Summer

Date of Graduation

2012

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Industrial and Managements Systems Engineering

Committee Chair

Steven E. Guffey.

Abstract

Capturing hoods are an important tool for protecting workers from hazardous airborne exposures and often preferred because their small sizes offers little interference to the worker or process. Current ventilation guidelines for capturing hood assume that exceeding a recommended capture velocity ensures an acceptable degree of effectiveness. That assumption has little basis in scientific studies. This study investigated the effectiveness of a 6 inch by 12 inch rectangular capturing hood centered on a work table with a manikin acting as a surrogate for a worker.;The study utilized a tracer gas (Freon-134a) to evaluate effectiveness of a capturing hood at three different hood airflows (Q), two different cross draft velocities (Vcross), and with the presence or absence of a flange (Flange). The tested air flows through the hood produced velocities at the leading edge of the source (Vx) of approximately 40, 100, and 140 fpm, as measured with a constant temperature anemometer. The study was conducted inside of a 9 ft high, 12 ft wide, 50 ft long wind tunnel with the manikin's back to the cross draft. Tracer gas was released from a custom made source located 11" in front of the capturing hood. The manikin was heated and "breathed." Its hands were positioned on either side of the source.;Breathing zone samples from the nose (Cnose) and mouth (Cmouth) of the manikin were collected simultaneously to evaluate the protection efficiency of the hood. Samples were also taken simultaneously from inside the duct (Cduct) to evaluate the capture efficiency of the hood. Samples were collected in 5 liter TedlarRTM bags at a rate of 0.2 lpm over a period of 20 minutes for each sample. Sample bag contents were analyzed by a Gastec FT-IR.;The study used a randomized factorial design with two replications. The results showed that the capturing hood was surprisingly highly effective both in terms of minimizing manikin exposures and minimizing escape of contaminant to the room environment. The concentration of Freon measured in the breathing zone was less than 1 ppm for all tests and mostly was below 0.2 ppm, even though the source concentration was over 370,000 ppm and was released at 1.79 lpm. This was true even when the capture velocity was only 50 fpm and the cross draft velocity was 60 fpm. The capture effectiveness of the hood was no less than 90% but the results may not have been reliable due to apparent measurement inaccuracies and imprecision at the Freon levels measured.;The results only apply to this hood under these conditions. Testing under broader ranges of conditions would be necessary before concluding that the capturing hood is always highly effective.

Download

Share

COinS