NCT Installation Standards & Best Practices 3 — Questions and Answers
Question 1: When installing HEPA filters in a critical environment, which test is performed in-place to verify filter integrity after installation?
- MERV rating test
- DOP/PAO aerosol challenge scan test (Correct answer)
- Pressure drop measurement only
- Visual inspection under UV light
Correct answer: DOP/PAO aerosol challenge scan test
An in-place DOP (dioctyl phthalate) or PAO (poly-alpha-olefin) aerosol scan test is the industry-standard method to verify installed HEPA filter integrity and detect pinhole leaks or frame bypass.
Question 2: What is the maximum allowable installed filter penetration per IEST-RP-CC034 for a HEPA filter scan test?
- 0.001%
- 0.01% (Correct answer)
- 0.05%
- 0.10%
Correct answer: 0.01%
IEST-RP-CC034 specifies that the maximum allowable local penetration during a HEPA in-place scan test is 0.01% of the upstream concentration.
Question 3: According to NAFA guidelines, which type of duct liner should NOT be installed immediately downstream of the final filter in a critical application?
- Sheet metal liner
- Exposed fiberglass duct liner (Correct answer)
- Galvanized steel liner
- Stainless steel liner
Correct answer: Exposed fiberglass duct liner
Exposed fiberglass duct liner downstream of the final filter can shed fibers into the clean air stream, contaminating areas the filtration system was designed to protect.
Question 4: What problem occurs when a filter holding frame is installed out of plumb in a vertical filter bank?
- Filter MERV rating decreases
- Filters may sag, causing bypass gaps at the top or sides (Correct answer)
- Static pressure increases excessively
- Filter color fades faster
Correct answer: Filters may sag, causing bypass gaps at the top or sides
An out-of-plumb frame allows filters to sag or shift under gravity, opening gaps that permit unfiltered air bypass and reduce filtration efficiency.
Question 5: What is the recommended minimum overlap between a filter gasket and its mating surface on a holding frame?
- 1/16 inch
- 1/4 inch (Correct answer)
- 3/8 inch
- 1/2 inch
Correct answer: 1/4 inch
A minimum 1/4-inch gasket contact with the frame mating surface ensures a reliable seal against bypass under operational static pressures.
Question 6: When should a filter holding frame be cleaned before installing new filters?
- Never — cleaning is optional
- Before every filter replacement to remove accumulated dirt that could compromise the new filter seal (Correct answer)
- Only during annual maintenance shutdowns
- Only if visible mold is present
Correct answer: Before every filter replacement to remove accumulated dirt that could compromise the new filter seal
Debris and dirt buildup on the frame seating surface prevents proper gasket compression, so the frame must be cleaned before each filter changeout to ensure a good seal.
Question 7: Which installation tool is used to verify that a filter is seated with adequate and uniform compression against the frame?
- Anemometer
- Calibrated torque wrench or compression gauge on retaining clips (Correct answer)
- Manometer
- Particle counter
Correct answer: Calibrated torque wrench or compression gauge on retaining clips
Calibrated retaining clip torque or a compression gauge ensures the gasket is compressed uniformly to the manufacturer's specification, preventing both under- and over-compression.
NCT Installation Standards & Best Practices 3
When installing HEPA filters in a critical environment, which test is performed in-place to verify filter integrity after installation?