CIH Engineering Controls and Ventilation 2 — Questions and Answers
Question 1: What is the primary purpose of a push-pull ventilation system in an industrial setting?
- Increase room temperature uniformity
- Improve contaminant capture at open-surface tanks (Correct answer)
- Reduce HVAC energy consumption
- Pressurize the work zone
Correct answer: Improve contaminant capture at open-surface tanks
Push-pull systems use an air supply (push) and exhaust (pull) to control contaminants at open-surface tanks, such as plating baths, by creating a horizontal airflow across the tank surface.
Question 2: When calculating the hood entry loss coefficient (F_h), which formula is correct for a plain duct opening (no flange)?
- F_h = 0.49 (Correct answer)
- F_h = 0.25
- F_h = 1.78
- F_h = 0.93
Correct answer: F_h = 0.49
A plain duct opening (unflanged) has a hood entry loss coefficient of approximately 0.49 velocity pressure units.
Question 3: In local exhaust ventilation, the 'centerline velocity' concept is used to describe:
- The airspeed at the geometric center of the duct cross-section
- The velocity along the axis of suction in front of a hood face (Correct answer)
- The mean velocity across the entire duct
- The velocity at the fan inlet
Correct answer: The velocity along the axis of suction in front of a hood face
Centerline velocity refers to the air velocity along the axis of a hood's suction field, used to determine the capture zone in front of the hood.
Question 4: Which of the following best describes a 'canopy hood' limitation in industrial hygiene?
- It cannot be used for hot processes
- It is effective only for very light contaminants
- Thermal plumes can carry contaminants past the worker before capture (Correct answer)
- It requires extremely high duct velocities
Correct answer: Thermal plumes can carry contaminants past the worker before capture
Canopy hoods placed above hot processes risk drawing the thermal plume through the worker's breathing zone before the contaminants reach the hood.
Question 5: The ACGIH Industrial Ventilation Manual recommends a minimum duct transport velocity for dry grinding dust of approximately:
- 1,000 fpm
- 2,500 fpm
- 4,500 fpm (Correct answer)
- 7,000 fpm
Correct answer: 4,500 fpm
Dry grinding operations generate heavy, abrasive particles requiring transport velocities of approximately 4,000–4,500 fpm to prevent settling in ducts.
Question 6: In a ventilation system with multiple branches, 'static pressure balancing' refers to:
- Setting all branch fans to equal RPM
- Adjusting branch duct dimensions or dampers so all branches have equal resistance (Correct answer)
- Ensuring all exhaust points operate at the same temperature
- Installing equal-length branches
Correct answer: Adjusting branch duct dimensions or dampers so all branches have equal resistance
Static pressure balancing ensures that the static pressure at each branch junction is equal, achieving design airflow in every branch without relying solely on dampers.
Question 7: A 'slot hood' is most commonly used for which type of industrial application?
- Capturing emissions from large grinding wheels
- Controlling emissions from long, narrow sources like open-surface tanks and conveyor lines (Correct answer)
- Providing general dilution ventilation for a work room
- Exhausting hot gases from furnace stacks
Correct answer: Controlling emissions from long, narrow sources like open-surface tanks and conveyor lines
Slot hoods feature a long, narrow opening that distributes suction evenly along the length of tanks, conveyor lines, or other elongated emission sources.
CIH Engineering Controls and Ventilation 2
What is the primary purpose of a push-pull ventilation system in an industrial setting?