Exam (elaborations)
CIH Ventilation (Hoods, Fans, Ducts) Questions and Answers 2024
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CIH Ventilation (Hoods, Fans, Ducts)
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CIH Ventilation (Hoods, Fans, Ducts)Push-pull exhaust system (exterior hood variation) - answer-Jet of air pushed across
contam source into flow field of hood (plating and open surface vessel operations)
-In push-pull ventilation system, push nozzle should be directed 0-20 degrees below
horizontal
-The pull air flow must be at least 150% of the push air
Slot hoods - answer Always preferred to to canopy hood at room temp
Requires less air flow than canopy hood design
The function of slot in slot hood - answer To provide uniform air distribution
Most adaptable to changes in equipment layout - answer A plenum-type exhaust
system
Hood design that requires lowest total air flow - answer Enclosing hood, one side open
Why slot hoods are inherently superior in perf - answer Capture velocity falls off more
slowly
Exterior hood - answerLocated adjacent to emission source (slot at edge of tank or
opening on welding table)
Important aspects: capture velocity, cross drafts, distance of contam to source
Enclosing hoods - answerSurrounds contaminant, prevents from escaping
Completely or partially enclose the process. (Glove box, lab hood, paint booth)
preferred method if possible
Requires less airflow than exterior hood
Enclosing hoods - answerHood face velocity important
Canopy hoods - answerAllow contaminant to pass through worker's breathing zone
Used for elevated temps
Backdraft hood - answerDraws air away from BZ towards equip rear
Shake out hood baffles - answerProvide better air distribution
Double duct's airflow - answerFriction loss quadruples
Blast gates - answerBalance resistance to airflow in ducts
, Dilution ventilation - answerUsed for low toxicity vapors
Reynolds number - answerDescribes flow (turbulent or laminar) in a duct
>4000 Re - answerTurbulent
<4000 Re - answerLaminar
Slot hood - answerLocal exhaust electroplating tank
Central vacuum - answerRemoves material/aerosols from the area
General ventilation - answerNot for particulate or toxic gases/vapors
Hood static pressure - answerEnergy necessary to move and accelerate air
50 fpm - answerPossible face velocity due to natural factors
Balance with blast gate - answerBranches of duct balance differential >0.1
Determine variation in fan speed - answerFan size, duct system & air density
Greatest capture velocity - answerNeeded for grinding operations
In IH air is considered - answerAn incompressible fluid
Round ducts are ______ than square ducts - answerStronger
Smoke tubes used in - answerWet air with velocities <150 fpm
Measures static pressure - answerU tube manometer, magnehelic gauge & inclined
manameter
Propeller fan - answerA wide selection of quality; rugged
Aspect ratio of an exhaust hood - answerRatio of width to length
Local exhaust ventilation - answerRemove contaminants at their source
Independent of slot air velocity - answerCapture velocity
Function of slot in slot hood - answerObtain proper air distribution
Change in static pressure - answerCauses air to move (high ➡️
low)
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