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Impact of Flow Separation on Exposure and Hood Capture Efficiency.

PB91188615

Publication Date	1990
Personal Author	Flynn, M. R.
Page Count	156
Abstract	A mathematical model was developed which could predict breathing zone concentration for a worker operating in the vicinity of a local exhaust hood. As part of the effort, a mathematical model was developed to predict breathing zone concentration for a mannequin when a point source of tracer was located downstream. The model was extended to include the situation with a mannequin positioned in front of a flanged circular hood and to include cross drafts and mannequin position with respect to the hood. The results of the study indicated that where workers hold contaminant generating sources and operate in front of or within large booth type hoods, the phenomenon of boundary layer separation was of major importance in determining exposure. Where possible the worker should maintain an orientation such that the line connecting the source and worker is a right angle to, not parallel to, the air stream. Vortex shedding plays the primary role in contaminant transport from the separated recirculation zone. The author concludes that ventilation when used as an engineering control must be used in conjunction with, and not in exclusion to, work practices.
Keywords	Industrial hygiene Ventilation Air sampling Mathematical models Occupational exposure Exhaust hoods Air flow Boundary layer separation Air pollution control Pollution transport Indoor air pollution Local exhaust ventilation
Source Agency	National Institute for Occupational Safety and Health
NTIS Subject Category	68A - Air Pollution & Control 94D - Job Environment 41I - Job Environment
Corporate Authors	North Carolina Univ. at Chapel Hill. Dept. of Environmental Sciences and Engineering.; National Inst. for Occupational Safety and Health, Cincinnati, OH.
Supplemental Notes	Sponsored by National Inst. for Occupational Safety and Health, Cincinnati, OH.
Document Type	Technical Report
Title Note	Final rept.
NTIS Issue Number	199116

Impact of Flow Separation on Exposure and Hood Capture Efficiency.

Impact of Flow Separation on Exposure and Hood Capture Efficiency.
PB91188615

Publication Date	1990
Personal Author	Flynn, M. R.
Page Count	156
Abstract	A mathematical model was developed which could predict breathing zone concentration for a worker operating in the vicinity of a local exhaust hood. As part of the effort, a mathematical model was developed to predict breathing zone concentration for a mannequin when a point source of tracer was located downstream. The model was extended to include the situation with a mannequin positioned in front of a flanged circular hood and to include cross drafts and mannequin position with respect to the hood. The results of the study indicated that where workers hold contaminant generating sources and operate in front of or within large booth type hoods, the phenomenon of boundary layer separation was of major importance in determining exposure. Where possible the worker should maintain an orientation such that the line connecting the source and worker is a right angle to, not parallel to, the air stream. Vortex shedding plays the primary role in contaminant transport from the separated recirculation zone. The author concludes that ventilation when used as an engineering control must be used in conjunction with, and not in exclusion to, work practices.
Keywords	Industrial hygiene Ventilation Air sampling Mathematical models Occupational exposure Exhaust hoods Air flow Boundary layer separation Air pollution control Pollution transport Indoor air pollution Local exhaust ventilation
Source Agency	National Institute for Occupational Safety and Health
NTIS Subject Category	68A - Air Pollution & Control 94D - Job Environment 41I - Job Environment
Corporate Authors	North Carolina Univ. at Chapel Hill. Dept. of Environmental Sciences and Engineering.; National Inst. for Occupational Safety and Health, Cincinnati, OH.
Supplemental Notes	Sponsored by National Inst. for Occupational Safety and Health, Cincinnati, OH.
Document Type	Technical Report
Title Note	Final rept.
NTIS Issue Number	199116