General Exhaust Ventilation (Module 7)

Question 1

What is natural ventilation?

Answer 1

no fans or other mechanical equipment to move air

Question 2

What are examples of mechanical ventilation?

Answer 2

HVAC, Dilute ventilation, local exhaust ventilation (LEV)

Question 3

What is dilute ventilation?

Answer 3

• sometimes called “general exhaust ventilation” (GEV)
• The dilution of contaminated air with uncontaminated air for the purpose of controlling potential airborne health hazards, fire and explosive conditions, odors, and nuisance type contaminants.

Question 4

What is local exhaust ventilation (LEV)?

Answer 4

• always involves fans, ducts and other components
• contain or capture at source
• more complicated than GEV

Question 5

What are influential factors of natural ventilation?

Answer 5

• Wind: air pressure differentials around a building
• Air moves in and out of openings and within building
• Convection: temperature differences change air density buoyancy effects.

Question 6

What are some descriptors of natural ventilation?

Answer 6

• Unpredictable, unreliable, changeable without warning

Question 7

Is natural ventilation reliable or easy to control?

Answer 7

No

Question 8

What is more satisfactory for health hazard control, LEV or DV?

Answer 8

LEV

Question 9

Where is dilution ventilation primarily effective for?

Answer 9

general work areas

Question 10

Does dilution ventilation sometimes use natural ventilation?

Answer 10

Yes

Question 11

What is the goal of dilution ventilation (GEV)

Answer 11

Goal is to achieve acceptable contaminant levels – may require large amounts of air if have high emission rates and/or to achieve very low levels

Question 12

What is an issue with dilution ventilation (GEV)?

Answer 12

Will still have highest levels near emission sources – possible overexposure when near sources

Question 13

What is the exact definiton of dilution ventilation?

Answer 13

• The removal of air from the entire workplace, and replacing it with clean air, or
• Provide clean air and mix it with the contaminated air in order to dilute the contaminant

Question 14

What is local exhaust ventilation (LEV)?

Answer 14

• Contaminant captured near points of release and removed from work area
• mechanical
• removes pollutants at source and better protects workers
  -less airflow and mitigation

Question 15

What system is preferred for highly toxic contaminants?

Answer 15

Local Exhaust ventilation (LEV)

Question 16

What is the purpose of industrial ventilation?

Answer 16

• To reduce airborne concentrations
• To reduce heat load (if cooler air is introduced to hot environment), fire/explosion hazards

Question 17

What is HVAC?

Answer 17

• Comfort (heating, cooling, humidity, odor)

Question 18

When do we use GEV?

Answer 18

• Contaminants are not very toxic
• Comfort (heating, cooling, humidity, odor)
• Exposures which are generally low
• Contaminants are primarily vapors, gases, or respirable aerosols
• Emission source uniform in time
• Emissions are widely dispersed
• Contaminants released over a large volume
• Emissions are not close to people
• Moderate climatic conditions prevail
• Incoming air is at moderate temperature
• Dilution air is less contaminated than indoor air

Question 19

What are the keys to understanding dilution ventilation?

Answer 19

• Maintain target concentration
• Understand source behavior
• Understand air mixing