Effects of Face Velocity, Flanges, and Mannikin Position on the Effectiveness of a Benchtop Enclosing Hood in the Absence of Cross-Drafts

Guffey, Steven E.; Barnea, Nir

doi:10.1202/0002-8894(1994)055<0132:eofvfa>2.0.co;2

Cited by 4 publications

(34 citation statements)

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“…A reasonable conjecture would be that a contamination source could easily mix between the wake zones and end up within the worker's breathing zone. This was supported by Guffey and Barnea (1994) and later by Tseng, Huang, Chen, and Chang (2006) and Tielemans, Schneider, Goede, Tischer, Warren, Kromhout, and Cherrie. (2008).…”

Section: Cross Draftsmentioning

confidence: 80%

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Effects of a Manikin on the Capture Efficiency and Protection Efficiency of a Small Rectangular Hood

Geissler¹

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The primary indicator of capturing hood effectiveness is widely assumed to be the "capture velocity" measured normal to the center of the hood face, at the furthest location of the contaminant source. The velocity required at this distance (Vx) is thought to correspond to the appropriate flow (Q) required to capture the contaminant. The adequacy of Vx as a surrogate for hood effectiveness has long been poorly understood and has been little studied. Few considerations of potentially disruptive parameters, such as draft velocity, hood orientation, and operator presence are made during the design phase. In this study, an anatomically correct heated, breathing, and moving manikin was used as a surrogate for a human hood operator. Velocity profiles of the capture envelope were obtained by particle image velocimetry (PIV) at three orientations (0˚, 90˚, 180˚), with respect to the cross drafts (30, 60, and 120 fpm) generated inside a large wind tunnel. The capturing hood fan speed was set to maintain the Q of nominal Vx values of 50, 100, and 200 fpm, as measured 11 inches away from the hood face, in a controlled environment. A condensation particle counter (CPC) was used to compare the capture efficiency and protection efficiency of the rectangular hood with the traditional, expensive, and time-consuming tracer gas method. Salt aerosols and Freon 134-A were released, at separate occasions, 11 inches away from the hood face. Measurements were taken within the duct (Cduct) and between the mouth and nose (CBreathingZone) of the manikin. Duct measurements (Cduct100) were also collected when the contaminant was directly fed into the duct, and breathing zone measurements were also conducted with the hood turned off (CBreathingZone100). The capture efficiency results of each method were compared, and no significant difference between the methods was found. With the CPC method established as a viable method, studies were conducted to test the effects of operator presence, movement, hood orientation, and cross drafts under the same conditions as the PIV study. All effects, except for manikin movement, were found to have a significant effect on hood performance. Manikin movement did, however, have a significant effect on contaminant concentrations within the breathing zone of the operator.

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Section: Cross Draftsmentioning

confidence: 80%

“…(2008). Guffey and Barnea (1994) found, using a tracer gas, that contaminant concentrations in the breathing zone were higher with the presence of a manikin than samples taken in the same locations without the presence of a manikin. Welling, et.…”

Section: Cross Draftsmentioning

confidence: 99%

Effects of a Manikin on the Capture Efficiency and Protection Efficiency of a Small Rectangular Hood

Geissler¹

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“…Benchtop enclosing hoods (Figure 1.1) are deemed the most effective type to protect workers from airborne contaminants in industrial processes (ACGIH ® Industrial Ventilation Committee, 2010). These simple enclosing hoods are an important tool for local exhaust ventilation (Guffey and Barnea, 1994). However, little has been published on factors affecting the effectiveness of benchtop enclosing hoods most used in industry.…”

Section: Introductionmentioning

confidence: 99%

“…Many factors affect hood performance, such as hood design elements, ambient air and worker temperature, hood face velocity (V face ), cross-draft velocity (V cross ), worker activities, and work practices (Altemose et al, 1998;Caplan and Knutson, 1982). Hood face velocity was shown to be an important factor in controlling worker exposure to pollutant contaminants in an enclosing hood (Guffey and Barnea, 1994) and it is often treated as a reliable guide to hood effectiveness (ACGIH ® Industrial Ventilation Committee, 2010). However, the practice of using only V face as factor to assess the lab hood's performance has been repeatedly questioned and thought as an inadequate criterion by Caplan and Knutson (1982).…”

Section: Introductionmentioning

confidence: 99%

“…Despite a diligent search, two experimental studies, Guffey and Barnea (1994) and He (2010), and two numerical studies, Dunnett (1994) and Karaismail and Celik (2010) are the only published studies about plain enclosing hood performance. They studied the effects of V face , V cross , worker orientation, flanges (He, 2010;Guffey and Barnea;1994), recirculating flow and airflow patterns on the performance of plain hoods (Dunnett, 1994;and Karaismail and Celik, 2010). However, although the effects of these factors on the performance of benchtop enclosing hoods were demonstrated with these studies, these results have not been validated with human subjects.…”

Section: Introductionmentioning

confidence: 99%

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Tracer Gas Exposure of Human Subjects Doing Simulated Work at a Benchtop Enclosing Hood in a Wind Tunnel

Carreno-Chavez¹

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Local exhaust ventilation devices (LEV) are critical in protecting workers from harmful airborne contaminants. The aim of this study is to investigate the factors that affect the performance of a benchtop enclosing hood. A Freon 134ahelium mixture was released from a 9" diameter pie-pan placed on the floor of a 30" high by 36" wide hood at 2" from the hood face. Freon 134a was measured close to the nose and mouth for a simple manikin (unheated and not breathing), a complex manikin (heated and breathing), and ten human subjects at different times while they stood at the face of the hood in a wind tunnel. Air was drawn from probe openings at the manikin and human subjects' faces at 0.20 lpm into 5 liter sampling bags for 20 minutes each. In a factorial study design, the manikins and the human subjects were tested at hood face velocity (V face) levels from 100 to 220 fpm and wind tunnel cross-draft velocity (V cross) levels from 14 to 63 fpm. The temperature difference (∆T) between the subject's body and the environment was also recorded. The results show that V face plays an important role on subjects' exposure. In general, the exposures decreased as V face increased. A statistically significant effect (p < 0.001) of V face on log-transformed exposure at the nose and mouth (log C nose and log C mouth) was found for both the simple manikin and the human subjects; in contrast, this effect was only found on log C mouth for the complex manikin. Crossv ACKNOWLEDGMENTS This dissertation was made possible by the love and constant support of all my family members. I feel so lucky to have them in my life. I would like to thank my parents Tomás and Doris, my brothers Wilmer and Edgardo, my sister Yliana, and my nieces Yanira and Issely for their unconditional love, support, and continuous encouragement during my studies at West Virginia University. I would like to give my sincere gratitude to my research advisor and committee chair Dr. Steven Guffey for his encouragement, support, and invaluable guidance through the different stages of this project. I learned many things from his expertise in the area during many hours of conversation. I would also like to thank my research co-advisor, Dr. Ismail Celik, for his initial support for the project and his insights and encouragement in this study.

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The effect of contaminant source location on worker exposure in the near-wake region

Kulmala

1996

The Annals of Occupational Hygiene

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The exposure of workers in the near-wake region due to a recirculating airflow was studied experimentally and numerically. A mannequin was installed in an open-ended tunnel and tracer gas was released at several locations downstream to determine the size and location of the reverse flow region. The contaminant transport into the breathing zone was found to depend strongly on the location of the release point. The airflow field was also determined numerically assuming a steady flow and using the standard k-epsilon turbulence model. After calculating the turbulent airflow field, a large number of submicrometre particles were released in different locations downstream of the mannequin to simulate the transport of gaseous contaminants. Although this method does not provide actual exposures, it does predict the tendencies in exposure variations due to different release points quite satisfactorily.

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Effects of Face Velocity, Flanges, and Mannikin Position on the Effectiveness of a Benchtop Enclosing Hood in the Absence of Cross-Drafts

Cited by 4 publications

References 0 publications

Effects of a Manikin on the Capture Efficiency and Protection Efficiency of a Small Rectangular Hood

Effects of a Manikin on the Capture Efficiency and Protection Efficiency of a Small Rectangular Hood

Tracer Gas Exposure of Human Subjects Doing Simulated Work at a Benchtop Enclosing Hood in a Wind Tunnel

The effect of contaminant source location on worker exposure in the near-wake region

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