CIH Engineering Controls and Ventilation 3 — Questions and Answers
Question 1: According to the Fan Laws, if fan speed is doubled while density and size remain constant, fan airflow will:
- Double (Correct answer)
- Increase by a factor of 4
- Increase by a factor of 8
- Remain unchanged
Correct answer: Double
The First Fan Law states that airflow (CFM) varies directly with fan speed (RPM), so doubling RPM doubles airflow.
Question 2: What is the purpose of an 'air-cleaning device' positioned upstream of a ventilation fan rather than downstream?
- To reduce fan motor heat exposure
- To protect the fan from abrasive or corrosive particulates in the exhaust stream (Correct answer)
- To increase fan efficiency
- To comply with OSHA makeup air requirements
Correct answer: To protect the fan from abrasive or corrosive particulates in the exhaust stream
Placing collection devices upstream of the fan protects fan blades from abrasive or corrosive contaminants, extending equipment life.
Question 3: Which type of industrial filter is best suited for capturing sub-micron particles from high-temperature exhaust streams?
- Wet scrubber
- Fabric baghouse
- High-temperature ceramic filter (Correct answer)
- Cyclone separator
Correct answer: High-temperature ceramic filter
Ceramic filters withstand high temperatures where fabric bags would be damaged, and they efficiently capture sub-micron particles that cyclones cannot.
Question 4: In dilution ventilation calculations, 'K factor' (mixing factor) is used to account for:
- Non-ideal mixing of supply air with room air (Correct answer)
- Temperature correction for the contaminant
- Fan efficiency losses
- Duct friction losses
Correct answer: Non-ideal mixing of supply air with room air
The K factor (typically 3–10) adjusts the theoretical ventilation rate upward to compensate for incomplete mixing of supply air with contaminated room air.
Question 5: The 'suction boundary' for a flanged circular hood compared to an unflanged hood at the same face velocity:
- Extends farther from the hood face (Correct answer)
- Extends the same distance but is wider
- Is shorter due to increased turbulence
- Is identical in shape and extent
Correct answer: Extends farther from the hood face
Flanging eliminates the reverse airflow behind the hood, directing more suction forward and extending the effective capture distance from the hood face.
Question 6: When designing a spray painting booth, which air distribution arrangement provides the most uniform airflow across the work piece?
- Side-draft with a single side exhaust
- Downdraft with a perforated floor exhaust (Correct answer)
- Crossdraft with overhead supply and side exhaust
- Updraft with floor-level supply and ceiling exhaust
Correct answer: Downdraft with a perforated floor exhaust
Downdraft booths supply clean air from the ceiling and exhaust through the floor, providing laminar, uniform airflow over the work piece and minimizing overspray exposure.
Question 7: The velocity pressure (VP) in a duct system is related to duct velocity by which relationship?
- VP = V / 4,005
- VP = (V / 4,005)² (Correct answer)
- VP = V × 4,005
- VP = √(V × 4,005)
Correct answer: VP = (V / 4,005)²
Velocity pressure in inches of water gauge equals (V/4,005)², where V is the duct velocity in fpm for standard air density.
CIH Engineering Controls and Ventilation 3
According to the Fan Laws, if fan speed is doubled while density and size remain constant, fan airflow will: